{"paper_id":"2e2b058f-320b-4702-b505-e210d124bc99","body_text":"α-Glucosidase inhibitory tetraoxygenated xanthones from the twig extract of Garcinia cowa Roxb. ex Choisy ​ | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article α-Glucosidase inhibitory tetraoxygenated xanthones from the twig extract of Garcinia cowa Roxb. ex Choisy ​ Thi Kim An Nguyen, Thanh Tra Nguyen, Lan Phuong Doan, Thi Tham Pham, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9035742/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 5 You are reading this latest preprint version Abstract Phytochemical investigation of the twigs of Garcinia cowa Roxb. ex Choisy (Clusiaceae), collected in Vietnam, led to the isolation of five tetraoxygenated xanthones, including three new compounds, namely norrubraxanthone ( 1 ), garcinone G ( 2 ), and garcinone H ( 3 ), together with two known compounds, α -mangostin ( 4 ) and rubraxanthone ( 5 ). The structures of the new compounds were elucidated by comprehensive spectroscopic analyses, including 1D and 2D NMR and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and by comparison with literature data. All isolated compounds were evaluated for their in vitro α -glucosidase inhibitory activity. Compounds 1 – 5 exhibited potent inhibitory effects, with IC₅₀ values ranging from 0.39 to 1.62 µM, which were significantly stronger than that of the positive control acarbose (IC₅₀ = 263.01 ± 10.92 µM). Among them, compounds 3 and 4 showed the most pronounced activity, with IC₅₀ values of 0.43 ± 0.01 and 0.39 ± 0.01 µM, respectively. Tetraoxygenated xanthone Garcinia cowa α-glucosidase antidiabetic Figures Figure 1 Figure 2 Introduction Type 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by persistent postprandial hyperglycemia and insulin resistance, representing a major global health burden. Inhibition of α -glucosidase, a key intestinal enzyme responsible for the terminal hydrolysis of carbohydrates into absorbable glucose, is an established therapeutic strategy to control postprandial blood glucose levels (Van de Laar, 2008). Although several synthetic α -glucosidase inhibitors, such as acarbose and miglitol, are clinically available, their long-term use is often associated with gastrointestinal side effects, prompting continuous interest in the discovery of safer and more effective inhibitors from natural sources (Derosa et al, 2012; Rahimi et al, 2005). Among natural secondary metabolites, xanthones constitute a structurally diverse class of polyphenolic compounds predominantly found in plants of the family Clusiaceae (Guttiferae). Xanthones have attracted considerable attention due to their wide spectrum of biological activities, including antioxidant, anti-inflammatory, anticancer (Oriola et al, 2024; Wahyuni et al, 2016), and antidiabetic effects (Bui et al, 2023; Yang et al, 2022; Nguyen et al, 2017). The genus Garcinia is recognized as one of the richest natural sources of oxygenated and prenylated xanthones, with numerous compounds displaying potent enzyme inhibitory and antidiabetic properties (Santos et al, 2018). The structure–activity relationship studies have suggested that highly oxygenated xanthones, particularly those bearing multiple free hydroxyl and/or methoxy substituents in A and B rings of the xanthone core display more efficacy for α -glucosidase inhibitory activity (Ryu et al, 2011). Garcinia cowa Roxb. ex Choisy, widely distributed in Southeast Asia including Vietnam, has been traditionally used in folk medicine for the treatment of inflammation, infections, and metabolic disorders (Pham, 1999). Phytochemical investigations of G. cowa have mainly focused on its bark (Ritthiwigrom et al, 2013), latex (Nguyen et al, 2022), root (An et al, 2023), fruits, flower (Sriyatep et al, 2015) and leaves (Raksat et al, 2020), leading to the identification of various oxygenated xanthones with notable biological activities. However, the chemical constituents of the twigs of G. cowa , particularly tetraoxygenated xanthones and their α -glucosidase inhibitory potential, remain insufficiently explored. In the present study, we report the isolation and structural elucidation of three new and two known tetraoxygenated xanthones from the twigs of Garcinia cowa collected in Vietnam, employing comprehensive chromatographic separation and spectroscopic analyses (1D and 2D NMR, HR-ESI-MS). Furthermore, the isolated compounds were evaluated for their in vitro α -glucosidase inhibitory activity to assess their potential as natural antidiabetic agents. This work not only expands the phytochemical knowledge of G. cowa but also highlights tetraoxygenated xanthones as promising leads for the development of novel α -glucosidase inhibitors of natural origin. Materials and Methods General Experimental Procedures Column chromatography (CC) was carried out on silica gel 60 (Merck, 5–40 µm), silica gel 100 (Merck, 63–200 µm), Sephadex LH-20 (GE Healthcare), and C 18 -reversed-phase silica gel (RP-18, Merck, 15–25 µm). Thin-layer chromatography (TLC) was performed on silica gel 60 F 254 aluminum plates (Merck, Germany). Visualization of TLC plates was performed under UV light ( λ 254 and 365 nm), staining with 5% vanillin/H 2 SO 4 in ethanol or 10% H 2 SO 4 solutions. NMR spectra were recorded on a AV 600 MHz spectrometer (Bruker, Germany). Chemical shifts are reported in δ (ppm) with tetramethylsilane (TMS) as an internal reference and coupling constants ( J ) are given in Hertz (Hz). HR-ESI-MS spectra were performed on an Sciex X500 Q-TOF LC/MS system. The UV spectra were recorded on a V-630 UV-VIS spectrophotometer (Jasco, Japan). Melting point was measured on a Büchi B-545 (USA) melting point apparatus (without correction). Industrial-grade solvents (China) used for column chromatography were distilled and dried over sodium sulfate just prior to use. Plant Material Fresh twigs of Garcinia cowa Roxb. ex Choisy were collected at Ba Vi, Hanoi, Vietnam in July 2024. The plant material was identified by Dr. Nguyen Quoc Binh, Vietnam National Museum of Nature, Vietnam Academy of Science and Technology (VAST). A voucher specimen No. GC072024 has been deposited at the Institute of Chemistry, VAST. Extraction and Isolation The twigs of G. cowa (5.0 kg) were dried in an oven at 45 o C for 3 days and subsequently ground into a fine powder. The powder materiel was extracted with ethanol (3 x 3 L) under ultrasonic vibration for 6 h at room temperature. The combined extract were filtred and concentrated under reduced pressure to yield a crude extract (312.4 g). The crude extract was then suspended in water and successively partitioned with n -hexane and ethyl acetate (EtOAc), and concentrated to afford the n -hexane fraction (98.1 g), the EtOAc fraction (182.4 g), and the remaining aqueous residue (31.8 g). The EtOAc fraction was separated by column chromatography (CC) over silica gel using gradient solvent systems of n -hexane/EtOAc (10/0 to 3/1, v/v) and dichloromethane/methanol (DCM/MeOH) (15/1 to 0/10, v/v) to provide seven main fractions (Frs. F1–F7). Fraction F3 (21.0 g) was fractioned using silica gel CC eluted with n -hexane/EtOAc (50/1 to 1/2, v/v) to obtain compound 4 (12.2 mg) and compound 5 (25.0 mg). Fraction F4 (35.9 g) was fractioned using silica gel CC eluted with n -hexane/acetone (30/1 to 0/10, v/v) to obtain six subfractions (Frs. F4.1-F4.6). Compound 1 (14.6 mg) was isolated from subfraction F4.5 by repeated CC over silica gel using DCM/MeOH (40/1, v/v) as the eluent, followed by crystallisation from a mixture of DCM/MeOH to appear as pale-yellow needles. Fraction F5 (13.8 g) was chromatographed on a silica gel column eluting with DCM/MeOH (50/1 to 3/1), v/v) to give five subfractions (Frs. F5.1-F5.5). Subfraction F5.3 was first separated on a Sephadex LH-20 column using eluent of 5% DCM/MeOH and then further purified by silica gel CC eluted with DCM/MeOH (35/1, v/v) to obtaine compound 2 (23.6 mg) as pale-yellow solid. Fraction F6 (8.6 g) was loaded onto a silica gel column eluted with DCM/MeOH (40/1–3/1, v/v) to yield five subfractions (Frs. F6.1-F6.5). Repeated chromatography of subfraction F6.2 by silica gel CC with DCM/MeOH (30/1, v/v) and further purification in a Sephadex LH-20 column using 5% DCM/MeOH to provide compound 3 (16.2 mg) which was recrystallized from methanol as pale-yellow needles. Norrubraxanthone ( 1 ): Pale yellow needles (MeOH-DCM). m.p. 216–217°C. IR (KBr) ν max : 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) λ max (log ɛ ): 203 (4,90), 212 (4,88), 244 (4,79), 260 (4,76), 316 (4,63), 353 (4,10). 1 H and 13 C NMR (CD 3 OD): see Table 1 . HR-ESI-MS (pos.): m/z 397.1646 [M + H] + ; calcd for C 23 H 25 O 6 + , 397.1646. Table 1 1 H (600 MHz) and 13 C (125 MHz) NMR data (in CD 3 OD) for compounds 1 – 3 . Position 1 2 3 δ H (mult., J ) δ C Position δ H (mult., J ) δ C δ H (mult., J ) δ C 1 164.6 1 161.5 161.6 2 6.09 (d, 1.8) 98.5 2 111.5 112.3 3 165.4 3 163.6 163.8 4 6.16 (d, 2.4) 93.8 4 6.21 (s) 93.2 6.26 (s) 93.2 4a 158.3 4a 156.1 156.2 5 6.65 (s) 101.0 5 6.68 (s) 103.0 6.73 (s) 103.0 5a 153.3 5a 156.6 156.7 6 65yt 154.1 6 157.8 158.0 7 142.1 7 144.7 144.8 8 129.5 8 137.6 137.7 8a 112.1 8a 112.1 112.1 9 183.3 9 183.1 183.2 9a 104.3 9a 103.7 103.7 1ʹ 4.09 (d, 6.6) 26.4 1ʹ 3.27 (d, 7.2) 22.2 2.70 (m) 28.9 2ʹ 5.25 (td, 6.6, 1.2) 124.8 2ʹ 5.24 (tt, 5.4, 1.8) 123.9 1.70 (m) 43.3 3ʹ 135.3 3ʹ 131.7 71.8 4ʹ 1.94 (m) 40.9 4ʹ 1.79 (s) 17.9 1.29 (s) 18.4 5ʹ 2.02 (m) 16.6 5ʹ 1.67 (s) 26.0 1.29 (s) 29.0 6ʹ 5.01 (m) 125.5 1ʺ 4.13 (d, 6.6) 26.6 4.17 (d, 6.6) 26.6 7ʹ 131.8 2ʺ 5.41 (t, 6.6) 127.8 5.41 (t, 6.6) 127.7 8ʹ 1.54 (s) 25.7 3ʺ 135.3 135.4 9ʹ 1.50 (s) 17.7 4ʺ 4.36 (s) 62.0 4.37 (s) 61.5 10ʹ 1.82 (s) 27.7 5ʺ 1.78 (s) 21.6 1.78 (s) 21.6 7-OMe 3.80 (s) 61.4 3.81 (s) 62.0 Garcinone G ( 2 ): Pale yellow powder. m.p. 206–207°C. IR (KBr) ν max : 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) λ max (log ɛ ): 210 (4,94), 243 (4.82), 260 (4.71), 316 (4.67), 358 (4.11). 1 H and 13 C NMR (CD 3 OD): see Table 1 . HR-ESI-MS (pos.): m/z 427.1756 [M + H] + ; calcd for C 24 H 27 O 7 + , 427.1757. Garcinone H ( 3 ): Pale yellow needles (MeOH-DCM); m.p. 214–215°C. IR (KBr) ν max : 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) λ max (log ɛ ): 208 (4,73), 243 (4,44), 259 (4,39), 315 (4,27), 346 (3,76). 1 H and 13 C NMR (CD 3 OD): see Table 1 . HR-ESI-MS (pos.): m/z 445.1866 [M + H] + ; calcd for C 24 H 29 O 8 + , 445.1857. α -Mangostin ( 4 ): Yellow powder. 1 H NMR (CDCl 3 ) δ (ppm): 13.77 (1H, OH), 6.77 (1H, s, H-5), 6.25 (1H, s, H-4), 5.28 (2H, m, H-2ʹ, H-2ʺ), 4.07 (2H, d, J = 6.6 Hz, H-1ʺ), 3.80 (3H, s, OMe), 3.42 (2H, d, J = 6.6 Hz, H-1ʹ), 1.85 (6H, s, H-4ʹ, H-4ʺ), 1.75 (3H, s, H-5ʹ), 1.69 (3H, s, H-5ʺ). 13 C NMR (CDCl 3 ) δ (ppm): 182.0 (C-9), 161.5 (C-3), 160.5 (C-1), 155.7 (C-6), 155.0 (C-5a), 154.6 (C-4a), 142.6 (C-7), 137.1 (C-8), 135.2 (C-3ʹ), 132.1 (C-3ʺ), 123.2 (C-2ʺ), 121.6 (C-2ʹ), 112.1 (C-8a), 108.8 (C-2), 103.6 (C-9a), 101.6 (C-5), 93.3 (C-4), 62.0 (7-OMe), 26.6 (C-1ʺ), 25.8 (C-4ʹ, 4ʺ), 21.4 (C-1ʹ), 18.2 &17.9 (C-5ʹ, 5ʺ). Rubraxanthone ( 5 ): Yellow powder. 1 H NMR (CDCl 3 ) δ (ppm): 6.63 (1H, s, H-5), 6.13 (1H, d, J = 1.8 Hz, H-4), 6.06 (1H, d, J = 1.8 Hz, H-2), 5,19 (1H, td, J = 6.0, 0.6 Hz, H-2ʹ), 4.99 (1H, td, J = 6.6, 1.2, H-6ʹ), 4.01 (2H, d, J = 6.6 Hz, H-1ʹ), 3.76 (3H, s, 7-OMe), 2.03 (2H, m, H-5ʹ), 1.95 (2H, m, H-4ʹ), 1.79 (3H, s, H-10ʹ), 1.54 (3H, s, H-8ʹ), 1.50 (3H, s. H-9ʹ). 13 C NMR (CDCl 3 ) δ (ppm): 181.5 (C-9), 164.3 (C-3), 163.2 (C-1), 156.9 (C-4a), 156.5 (C-6), 155.3 (C-5a), 143.4 (C-7), 137.2 (C-3ʹ), 133.9 (C-7ʹ), 130.5 (C-8), 124.1 (C-6ʹ), 123.9 (C-2ʹ), 110.8 (C-8a), 102.5 (C-9a), 101.5 (C-5), 97.4 (C-2), 92.7 (C-4), 60.0 (7-OMe), 39.4 (C-4ʹ), 26.2 (C-10ʹ), 25.6 (C-1ʹ), 24.4 (C-8ʹ), 16.4 (C-9ʹ), 15.3 (C-5ʹ). α -Glucosidase inhibition assay The α -glucosidase inhibitory assay was performed following a previously reported method with minor modifications (An et al, 2023; Hakamata et al, 2009). The test compounds were initially dissolved in dimethyl sulfoxide (DMSO) and subsequently diluted with phosphate buffer (100 mM, pH 6.8) to final concentrations of 16, 4, 1, 0.25 and 0.06 µg/mL. In a 96-well microplate, each reaction well contained 40 µL of phosphate buffer (100 mM, pH 6.8), 10 µL of the test compound solution, and 25 µL of α -glucosidase (0.4 U/mL, Sigma). The mixture was pre-incubated at 37°C for 10 min, after which 25 µL of p -nitrophenyl- α - D -glucopyranoside (pNPG, 2.5 mM, Sigma) was added to initiate the reaction. Following incubation at 37°C for 30 min, the reaction was terminated by the addition of 100 µL of Na₂CO₃ (0.2 M). A reaction mixture without test compound served as the negative control, while acarbose was used as the positive control. All experiments were conducted in triplicate. The amount of p -nitrophenol released was quantified by measuring absorbance at 410 nm using a microplate reader (BioTek, USA). α -Glucosidase inhibitory activity was expressed as percentage inhibition and calculated using the following equation: Inhibition (%) = [(OD control – OD sample) / OD control] x 100. The IC₅₀ value, defined as the concentration of compound required to inhibit 50% of α -glucosidase activity, was determined using TableCurve software. Statistical analysis All quantitative data are presented as mean ± standard deviation (SD) from at least three independent experiments (n ≥ 3). IC₅₀ values were calculated using TableCurve 2D v4 (Systat Software), in accordance with the original protocol. Differences were considered statistically significant at p < 0.05. Results and Discussion Isolation and structure elucidation The ethyl acetate extract of the twigs of G. cowa was separated by column chromatography to afford five tetraoxygenated xanthones, including 3 new xanthones, namely norrubraxanthone ( 1 ), garcinone G ( 2 ), and garcinone H ( 3 ), and two known xanthones, α-mangostin ( 4 ) and rubraxanthone ( 5 ) (Fig. 1 ). Norrubraxanthone ( 1 ) was obtained as pale-yellow needles, m.p. 215–216 o C. The positive ion HR-ESI-MS spectrum of 1 exhibited a protonated molecular ion peak at m/z 397.1646 [M + H] + , consistent with molecular fomular C 23 H 24 O 6 . The 1 H and 13 C NMR spectra displayed characteristic resonances of a 1,3,6,7-tetraoxygenated xanthone, including a conjugated carbonyl carbon ( δ C 183.3, C-9), three isolated aromatic methines [ δ H 6.65 (1H, s, H-5)/ δ C 101.0 (C-5), δ H 6.16 (1H, d, J = 2.4 Hz, H-4)/ δ C 93.8 (C-4) and δ H 6.09 (1H, d, J = 1.8 Hz, H-2)/ δ C 98.5 (C-2)], and six oxygenated aromatic carbons resonating at δ C 142.1-165.6. The presence of a geranyl side chain was established from HSQC and HMBC data, which revealed two olefinic methines [ δ H 5.25 (1H, td, J = 6.6, 1.2 Hz, H-2ʹ)/ δ C 124.8 (C-2ʹ) and δ H 5.01 (1H, m, H-6ʹ)/ δ C 125.5 (C-6ʹ)], three methylene groups [ δ H 4.09 (2H, d, J = 6.6, H-1ʹ)/ δ C 26.4 (C-1ʹ), δ H 2.02 (2H, m, H-5ʹ)/ δ C 16.6 (C-5ʹ) and δ H 1.94 (2H, m, H-4ʹ)/ δ C 40.9 (C-4ʹ)], three methyl groups [ δ H 1.82 (s, 3H, H-10ʹ)/ δ C 27.7 (C-10ʹ), δ H 1.54 (s, 3H, H-8ʹ)/ δ C 25.7 (C-8ʹ) and δ H 1.50 (s, 3H, H-9ʹ)/ δ C 17.7(C-9ʹ)] and two quaternary olefinic carbons [ δ C 135.3 (C-3ʹ) and δ C 131.8 (C-7ʹ)]. The attachment of the geranyl side chain at C-8 was confirmed by HMBC correlations from H-1ʹ to C-7 ( δ C 142.1), C-8 ( δ C 129.5) and C-8a ( δ C 112.1) (Fig. 2 ). Furthermore, the spectroscopic data of compound 1 (Table 1 ) were closely comparable to those reported for 1,3,6-trihydroxy-7-methoxy-8-(3,7-dimethyloct-2,6-dienyl)xanthone (rubraxanthone) previously isolated from G. cowa and G. nitida (Wahyuni et al, 2016), except for the absence of a methoxyl group. On the basis of detailed 1D and 2D NMR analyses and comparison with literature data, compound 1 was identified as 1,3,6,7-tetrahydroxy-8-(3,7-dimethyloct-2,6-dien-1-yl)xanthone. Garcinone G ( 2 ) was obtained as a pale-yellow powder, m.p. 206–207 o C. Its molecular formula was determined to be C 24 H 26 O 7 based on (+)HR-ESI-MS data, which showed a protonated molecular ion at m/z 427.1756 [M + H] + . The 1 H, and 13 C NMR spectra, together with HSQC data (Table 1 ), revealed the presence of two isolated aromatic methines [ δ H 6.68 (1H, s, H-5)/ δ C 103.0 (C-5), δ H 6.21 (1H, s, H-4)/ δ C 93.2 (C-4)], two olefinic methines [ δ H 5.41 (1H, t, J = 6.6 Hz, H-2ʺ)/ δ C 127.8 (C-2ʺ), δ H 5.24 (1H, tt, J = 5.4, 1.8 Hz, H-2ʹ)/ δ C 123.9 (C-2ʹ)], one methoxy group [ δ H 3.80 (3H, s, -OCH 3 )/ δ C 61.4], one oxygenated methylene [ δ H 4.36 (2H, s, H-4ʺ)/ δ C 62.0 (C-4ʺ)] and three methyl groups [ δ H 1.79 (3H, s, H-4ʹ)/ δ C 17.9 (C-4ʹ), δ H 1.78 (3H, s, H-5ʺ)/ δ C 21.6 (C-5ʺ) and δ H 1.67 (3H, s, H-5ʹ)/ δ C 26.0 (C-5ʹ)]. In addition, the presence of a conjugated carbonyl carbon at ( δ C 183.1, C-9) and six oxygenated aromatic carbons resonating at δ C 144.7-163.6 supported a tetraoxygenated xanthone skeleton bearing a prenyl and a hydroxylated prenyl side chain. The HMBC correlation between the methoxy protons and C-7 ( δ C 144.7) established the position of the methoxy substituent. The prenyl group was assigned to C-2 based on long-range HMBC correlations from H-1ʹ ( δ H 3.27 (2H, d, J = 7.2 Hz) to C-1 ( δ C 161.5), C-2 ( δ C 111.5), and C-3 ( δ C 163.6). Furthermore, the attachment of the 4-hydroxy-3-methylbut-2-en-1-yl side chain at C-8 was confirmed by HMBC cross-peaks from H-1ʺ ( δ H 4.13 (2H, d, J = 6.6 Hz) to C-7, C-8 ( δ C 137.6) and C-8a ( δ C 112.1) (Fig. 2 ). Accordingly, compound 2 was identified as 1,3,6-trihydroxy-7-methoxy-2-(3-methylbut-2-en-1-yl)-8-(4-hydroxy-3-methylbut-2-en-1-yl)xanthone and was named garcinone G. Garcinone H ( 3 ) was isolated as pale-yellow needles, m.p. 214–215 o C. The (+)HR-ESI-MS spectrum of 3 exhibited a protonated molecular ion peak at m/z 445.1866 [M + H] + , corresponding to the molecular formula C 24 H 28 O 8 . The 1 H and 13 C NMR data of 3 (Table 1 ) showed characteristic signals of a tetraoxygenated xanthone bearing two prenyl-derived side chains, closely resembling those of compound 2 . These included a conjugated carbonyl carbon ( δ C 183.2, C-9), two isolated aromatic methines [ δ H 6.73 (1H, s, H-5)/ δ C 103.0 (C-5), δ H 6.26 (1H, s, H-4)/ δ C 93.2 (C-4)], one olefinic methine [ δ H 5.41 (1H, t, J = 6.6 Hz, H-2ʺ)/ δ C 127.7 (C-2ʺ)], one methoxy group [ δ H 3.81 (3H, s, -OCH 3 )/ δ C 61.0], one oxygenated methylene [ δ H 4.37 (2H, s, H-4ʺ)/ δ C 61.5 (C-4ʺ)], three methyl groups [ δ H 1.78 (3H, s, H-5ʺ)/ δ C 21.6 (C-5ʺ), δ H 1.29 (6H, s, H-4ʹ, H-5ʹ)/ δ C 18.4 (C-4ʹ), 29.0 (C-5ʹ)] and six oxygenated aromatic carbons resonating at δ C 144.8-163.8. The major difference between compounds 2 and 3 was that the prenyl group attached at C-2 in 3 was hydroxylated and fully saturated. This was supported by the presence of two methylene groups [ δ H 2.70 (2H, m, H-1ʹ)/ δ C 28.9 (C-1ʹ), δ H 1.70 (2H, m, H-2')/ δ C 43.3 (C-2ʹ)], two methyl groups [ δ H 1.29 (6H, s, H-4', H-5')/ δ C 18.4 (C-4ʹ), 29.0 (C-5ʹ)] and an sp 3 oxygenated quaternary carbon at δ C 71.8 (C-3ʹ). Further support was provided by HMBC correlations from H-1ʹ to C-1 ( δ C 161.6), C-2 ( δ C 112.3), and C-3 ( δ C 163.8). All remaining spectroscopic features of compound 3 were identical to those of compound 2 . Accordingly, compound 3 was identified as 1,3,6-trihydroxy-7-methoxy-2-(3-hydroxy-3-methylbut-1-yl)-8-(4-hydroxy-3-methylbut-2-en-1-yl)xanthone (Fig. 2 ). Compounds 4 and 5 were identified as α -mangostin (Khaw et al, 2020) and rubraxanthone (Wahyuni et al, 2016) respectively. α-Glucosidase inhibition effects All isolated compounds ( 1 – 5 ) exhibited potent α -glucosidase inhibitory activity, with IC₅₀ values ranging from 0.39 to 1.62 µM (Table 2 ). These values indicate substantially stronger inhibition compared to the positive control acarbose (IC₅₀ = 263.01 ± 10.92 µM). Table 2 α -Glucosidase inhibition of compounds 1 – 5 Compound IC 50 (µM) 1 1.62±0.05 2 0.94±0.14 3 0.43 ± 0.01 4 0.39 ± 0.01 5 0.56 ± 0.03 Acarbose 263.01±10.92 Among the tested compounds, compounds 3 and 4 displayed the strongest inhibitory activity, with IC₅₀ values of 0.43 ± 0.01 µM and 0.39 ± 0.01 µM, respectively. These findings suggest that subtle structural differences among the tetraoxygenated xanthones influence their interaction with the enzyme active site. Compounds 2 and 5 also showed strong inhibition, with IC₅₀ values below 1 µM, whereas compound 1 exhibited comparatively weaker activity (IC₅₀ = 1.62 ± 0.05 µM), though still markedly more potent than acarbose. The low IC₅₀ values observed for these tetraoxygenated xanthones are consistent with previous reports describing highly oxygenated xanthones from Garcinia species, which have been shown to act as competitive or mixed-type α-glucosidase inhibitors (An et al, 2023, Nguyen et al, 2017; Tran et al, 2025, Yang et al, 2022). Overall, these findings suggest that the twigs of Garcinia cowa represent a promising source of bioactive xanthones and warrant further mechanistic studies, including enzyme kinetics, molecular docking, and in vivo evaluation. Conclusions In summary, a phytochemical investigation of the twigs of Garcinia cowa collected in Vietnam led to the isolation of five xanthone derivatives, among which three compounds ( 1 – 3 ) were identified as new natural products. Their structures were unambiguously elucidated using extensive spectroscopic analyses, including 1D and 2D NMR and HR-ESI-MS techniques. All isolated xanthones exhibited remarkably potent α -glucosidase inhibitory activity, with IC₅₀ values in the low micromolar to submicromolar range (0.39–1.62 µM), demonstrating activities several hundred times stronger than that of the reference drug acarbose. Notably, compounds 3 and 4 showed the most pronounced inhibitory effects, underscoring the importance of highly oxygenated xanthone frameworks in α -glucosidase inhibition. These findings not only expand the chemical diversity of xanthones reported from Garcinia cowa but also identify tetraoxygenated xanthones as promising lead compounds for the development of novel antidiabetic agents. Further studies focusing on enzyme inhibition mechanisms, structure-activity relationships, and in vivo antidiabetic efficacy are warranted. Declarations Author contributions NTKA, and TTTT contributed to the isolation and structure elucidation. DLP, PTT and NTT were responsible for testing and analysis of bioactivity assessments. NTKA, and TTTT worked on methods, software and prepared the manuscript. All authors approved the final manuscript and agreed to the submission. Funding This work was supported by the Vietnam Academy of Science and Technology (VAST04.02/25-26). Ethics approval All experimental procedures involving plant materials were conducted in accordance with institutional, national, and international ethical standards. This study did not involve experiments with human participants or animals. Consent to participate Not applicable. Consent to publish Not applicable. Competing interests The authors declare that they have no financial or personal conflicts of interest that could have influenced the work reported in this paper. References An NTK, Hien NV, Thuy NT, Phuong DL, Bach HG, Tra NT, Tung NQ, Tham PT, Tai BH, Thuy TTT (2023). Garcicowanones C-E, three new hydrated-geranylated xanthones from the roots of Garcinia cowa Roxb. ex Choisy, and their α -glucosidase inhibition activities. Nat Prod Res 37(21):3668-3676. https://doi: 10.1080/14786419.2022.2098956. Bui DN, Nguyen LTT, Nguyen L-TT, Ngo NTN, Tran PT, Nguyen HT, Dang LTN, Nguyen L-HD, Trinh BTD (2023). Two new antidiabetic xanthones from the twigs of Garcinia oblongifolia . Nat Prod Res 37(15): 2541-2550. https://doi.org/10.1080/14786419.2022.2055016. Derosa G, Maffioli P (2012) α -Glucosidase inhibitors and their use in clinical practice. Arch Med Sci 8(5):899–906. https://doi.org/10.5114/aoms.2012.31621. Hakamata W, Kurihara M, Okuda H, Nishio T, Oku T. (2009). Design and screening strategies for α -glucosidase inhibitors based on enzymological information. Curr Top Med Chem 9(1): 3-12. https://doi.org/10.2174/156802609787354306. Khaw KY, Ong YS, Goh B-H (2020). A rapid method for the retrieval of bioactive xanthone from Garcinia mangostana : A case study of α -mangostin. Prog Drug Discov Biomed Sci 3(1):1-5. https://doi.org/10.36877/pddbs.a0000072. Lebovitz HE MD (1997). Alpha-glucosidase inhibitors. Endoc Metabol Clin North Ame 26(3):539-551. https://doi.org/10.1016/s0889-8529(05)70266-8. Nguyen NK, Truong XA, Bui TQ, Bui DN, Nguyen HX, Tran PT, Nguyen LD (2017). Alpha-glucosidase inhibitory xanthones from the roots of Garcinia fusca . Chem Biodivers 14(10): e1700232. https://doi: 10.1002/cbdv.201700232. Nguyen TKA, Nguyen BN, Hoang TMN, Doan LP, Phan MG, Lee H, Kim DW, Lee JW, Tran TTT (2022). Six New Polyoxygenated Xanthones from Garcinia cowa and Their Neuroprotective Effects on Glutamate-Mediated Hippocampal Neuronal HT22 Cell Death. Chem Biodiver 19(9): e202200376. https://doi: 10.1002/cbdv.202200376. Oriola AO, Kar P (2024). Naturally occurring xanthones and their biological implications. Molecules 29(17):4241. https://doi.org/10.3390/molecules29174241. Pham HH (1999). An illustrated flora of Vietnam (in vietnamese). Youth Publishing House, 450. Raksat A, Phukhatmuen P, Yang J, Maneerat W, Charoensup R, Andersen RJ, Wang YA, Pyne SG, Laphookhieo S (2020). Phloroglucinol benzophenones and xanthones from the leaves of Garcinia cowa and their nitric oxide production and alpha-glucosidase inhibitory activities. J Nat Prod 83: 164–168. https://doi.org/10.1021/acs.jnatprod.9b00849. Rahimi R, Nikfar S, Larijani B, Abdollahi M (2005) A review on the role of antioxidants in the management of diabetes and its complications. Biomed Pharmacother 59:365–373. https:// doi.org/10.1016/j.biopha.2005.07.002. Ritthiwigrom T, Laphookhieo S, Pyne SG (2013). Chemical constituents and biological activities of Garcinia cowa Roxb. Maejo Int J Sci Technol 7:212–231. https://doi.org/10.14456/ mijst.2013.18. Ryu HW, Cho JK, Curtis-Long MJ, Yuk HJ, Kim YS, Jung S, Kim YS, Lee BW, Park KH (2011). α -Glucosidase inhibition and antihyperglycemic activity of prenylated xanthones from Garcinia mangostana . Phytochem 72(17):2148-2154. https://doi.org/ 10.1016/j.phytochem. 2011.08.007. Santos CMM, Freitas M, Fernandes E (2018). A comprehensive review on xanthone derivatives as α -glucosidase inhibitors. Eur J Med Chem 157:1460-1479. https://doi.org/10.1016/j.ejmech. 2018. 07.073. Sriyatep T, Siridechekorn I, Maneerat W, Pansanit A, Ritthiwigron T, Andersen RJ, Laphookhieo S (2015). Bioactive prenylated xanthones from the young fruits and flowers of Garcinia cowa . J Nat Prod 78:265–271. https://doi.org/10.1021/np5008476. Tran QHN, Nguyen HTM, Nguyen TH, Nguyen TTL, Sichaem J, Do LTM (2025). New α -glucosidase inhibitory xanthones from the fruits of Garcinia schomburgkiana . Nat Prod Res 39(18): 5258-5263. https://doi.org/10.1080/14786419.2024.2367011 Yang L, Zhang D, Li JB, Zhang X, Zhou N, Zhang WY, Lu H (2022). Prenylated xanthones with alpha-glucosidase and alpha-amylase inhibitory effects from the pericarp of Garcinia mangostana . J Asian Nat Prod Res 24(7):624-633. https://doi.org/10.1080/10286020.2021. 1967328. Van de Laar FA (2008). Alpha-glucosidase inhibitors in the early treatment of type 2 diabetes. Varc Health Risk Manag 4(6):1189-1195. https://doi.org/10.2147/VHRM.S3119. Wahyuni FS, Shaari K, Stanslas J, Lajis NHJ, Hamidi D (2016). Cytotoxic properties and complete nuclear magnetic resonance assignment of isolated xanthones from the root of Garcinia cowa Roxb. Pharmacogn Mag 12(1):S52-S56. https://doi.org/10.4103/0973-1296.176115. Supplementary Files Supplementarymaterialinfo.docx Graphicalabtract.pdf Supportinginformation.pdf Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 13 Apr, 2026 Reviewers invited by journal 13 Apr, 2026 Editor invited by journal 07 Apr, 2026 Editor assigned by journal 20 Mar, 2026 First submitted to journal 12 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-9035742\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Research Article\",\"associatedPublications\":[],\"authors\":[{\"id\":622265858,\"identity\":\"6791846d-617c-4a49-b6ed-2b7da2ec65d7\",\"order_by\":0,\"name\":\"Thi Kim An Nguyen\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Hanoi University of Industry\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Thi\",\"middleName\":\"Kim An\",\"lastName\":\"Nguyen\",\"suffix\":\"\"},{\"id\":622265859,\"identity\":\"93e7aac0-0ec9-425c-b12d-56f2a01911d6\",\"order_by\":1,\"name\":\"Thanh Tra 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\\u003cstrong\\u003e1\\u003c/strong\\u003e-\\u003cstrong\\u003e5\\u003c/strong\\u003e\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"1.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/b66bdd49edba8ffb28be1598.png\"},{\"id\":107320958,\"identity\":\"c8455433-51be-4d57-8830-ad8c5d8b4e52\",\"added_by\":\"auto\",\"created_at\":\"2026-04-20 10:28:31\",\"extension\":\"png\",\"order_by\":2,\"title\":\"Figure 2\",\"display\":\"\",\"copyAsset\":false,\"role\":\"figure\",\"size\":86825,\"visible\":true,\"origin\":\"\",\"legend\":\"\\u003cp\\u003eSelected HMBC correlations in compounds \\u003cstrong\\u003e1\\u003c/strong\\u003e-\\u003cstrong\\u003e3\\u003c/strong\\u003e.\\u003c/p\\u003e\",\"description\":\"\",\"filename\":\"2.png\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/c3a9a2c540557ea4fe7ef2bf.png\"},{\"id\":107487947,\"identity\":\"7541fbeb-b741-456f-bf2b-1512fe6d7a2e\",\"added_by\":\"auto\",\"created_at\":\"2026-04-22 02:43:08\",\"extension\":\"pdf\",\"order_by\":0,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"manuscript-pdf\",\"size\":675122,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"manuscript.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/91160fde-9dfd-4284-ab90-d75451530345.pdf\"},{\"id\":107486657,\"identity\":\"014e54b1-3058-40ff-a3ac-df14be65c987\",\"added_by\":\"auto\",\"created_at\":\"2026-04-22 02:38:36\",\"extension\":\"docx\",\"order_by\":1,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":13545,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Supplementarymaterialinfo.docx\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/f3a3eb035c795f387c3e23a1.docx\"},{\"id\":107320960,\"identity\":\"7835f4bd-d8d9-4eb7-8078-c20d569be424\",\"added_by\":\"auto\",\"created_at\":\"2026-04-20 10:28:31\",\"extension\":\"pdf\",\"order_by\":2,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":150781,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Graphicalabtract.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/20b7813fec918486409c1f79.pdf\"},{\"id\":107320956,\"identity\":\"adf735f9-26ad-4886-98c4-55e4e1463314\",\"added_by\":\"auto\",\"created_at\":\"2026-04-20 10:28:31\",\"extension\":\"pdf\",\"order_by\":3,\"title\":\"\",\"display\":\"\",\"copyAsset\":false,\"role\":\"supplement\",\"size\":1386184,\"visible\":true,\"origin\":\"\",\"legend\":\"\",\"description\":\"\",\"filename\":\"Supportinginformation.pdf\",\"url\":\"https://assets-eu.researchsquare.com/files/rs-9035742/v1/164cca3d4a0614dc8b2acebc.pdf\"}],\"financialInterests\":\"\",\"formattedTitle\":\"α-Glucosidase inhibitory tetraoxygenated xanthones from the twig extract of Garcinia cowa Roxb. ex Choisy ​\",\"fulltext\":[{\"header\":\"Introduction\",\"content\":\"\\u003cp\\u003eType 2 diabetes mellitus (T2DM) is a chronic metabolic disorder characterized by persistent postprandial hyperglycemia and insulin resistance, representing a major global health burden. Inhibition of \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase, a key intestinal enzyme responsible for the terminal hydrolysis of carbohydrates into absorbable glucose, is an established therapeutic strategy to control postprandial blood glucose levels (Van de Laar, 2008). Although several synthetic \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitors, such as acarbose and miglitol, are clinically available, their long-term use is often associated with gastrointestinal side effects, prompting continuous interest in the discovery of safer and more effective inhibitors from natural sources (Derosa et al, 2012; Rahimi et al, 2005).\\u003c/p\\u003e \\u003cp\\u003eAmong natural secondary metabolites, xanthones constitute a structurally diverse class of polyphenolic compounds predominantly found in plants of the family Clusiaceae (Guttiferae). Xanthones have attracted considerable attention due to their wide spectrum of biological activities, including antioxidant, anti-inflammatory, anticancer (Oriola et al, 2024; Wahyuni et al, 2016), and antidiabetic effects (Bui et al, 2023; Yang et al, 2022; Nguyen et al, 2017). The genus \\u003cem\\u003eGarcinia\\u003c/em\\u003e is recognized as one of the richest natural sources of oxygenated and prenylated xanthones, with numerous compounds displaying potent enzyme inhibitory and antidiabetic properties (Santos et al, 2018). The structure\\u0026ndash;activity relationship studies have suggested that highly oxygenated xanthones, particularly those bearing multiple free hydroxyl and/or methoxy substituents in A and B rings of the xanthone core display more efficacy for \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitory activity (Ryu et al, 2011).\\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. ex Choisy, widely distributed in Southeast Asia including Vietnam, has been traditionally used in folk medicine for the treatment of inflammation, infections, and metabolic disorders (Pham, 1999). Phytochemical investigations of \\u003cem\\u003eG. cowa\\u003c/em\\u003e have mainly focused on its bark (Ritthiwigrom et al, 2013), latex (Nguyen et al, 2022), root (An et al, 2023), fruits, flower (Sriyatep et al, 2015) and leaves (Raksat et al, 2020), leading to the identification of various oxygenated xanthones with notable biological activities. However, the chemical constituents of the twigs of \\u003cem\\u003eG. cowa\\u003c/em\\u003e, particularly tetraoxygenated xanthones and their \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitory potential, remain insufficiently explored.\\u003c/p\\u003e \\u003cp\\u003eIn the present study, we report the isolation and structural elucidation of three new and two known tetraoxygenated xanthones from the twigs of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e collected in Vietnam, employing comprehensive chromatographic separation and spectroscopic analyses (1D and 2D NMR, HR-ESI-MS). Furthermore, the isolated compounds were evaluated for their \\u003cem\\u003ein vitro α\\u003c/em\\u003e-glucosidase inhibitory activity to assess their potential as natural antidiabetic agents. This work not only expands the phytochemical knowledge of \\u003cem\\u003eG. cowa\\u003c/em\\u003e but also highlights tetraoxygenated xanthones as promising leads for the development of novel \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitors of natural origin.\\u003c/p\\u003e\"},{\"header\":\"Materials and Methods\",\"content\":\"\\u003cdiv id=\\\"Sec3\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eGeneral Experimental Procedures\\u003c/h2\\u003e \\u003cp\\u003eColumn chromatography (CC) was carried out on silica gel 60 (Merck, 5\\u0026ndash;40 \\u0026micro;m), silica gel 100 (Merck, 63\\u0026ndash;200 \\u0026micro;m), Sephadex LH-20 (GE Healthcare), and C\\u003csub\\u003e18\\u003c/sub\\u003e-reversed-phase silica gel (RP-18, Merck, 15\\u0026ndash;25 \\u0026micro;m). Thin-layer chromatography (TLC) was performed on silica gel 60 F\\u003csub\\u003e254\\u003c/sub\\u003e aluminum plates (Merck, Germany). Visualization of TLC plates was performed under UV light (\\u003cem\\u003eλ\\u003c/em\\u003e 254 and 365 nm), staining with 5% vanillin/H\\u003csub\\u003e2\\u003c/sub\\u003eSO\\u003csub\\u003e4\\u003c/sub\\u003e in ethanol or 10% H\\u003csub\\u003e2\\u003c/sub\\u003eSO\\u003csub\\u003e4\\u003c/sub\\u003e solutions. NMR spectra were recorded on a AV 600 MHz spectrometer (Bruker, Germany). Chemical shifts are reported in \\u003cem\\u003eδ\\u003c/em\\u003e (ppm) with tetramethylsilane (TMS) as an internal reference and coupling constants (\\u003cem\\u003eJ\\u003c/em\\u003e) are given in Hertz (Hz). HR-ESI-MS spectra were performed on an Sciex X500 Q-TOF LC/MS system. The UV spectra were recorded on a V-630 UV-VIS spectrophotometer (Jasco, Japan). Melting point was measured on a B\\u0026uuml;chi B-545 (USA) melting point apparatus (without correction). Industrial-grade solvents (China) used for column chromatography were distilled and dried over sodium sulfate just prior to use.\\u003c/p\\u003e \\u003c/div\\u003e\\n\\u003ch3\\u003ePlant Material\\u003c/h3\\u003e\\n\\u003cp\\u003eFresh twigs of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. ex Choisy were collected at Ba Vi, Hanoi, Vietnam in July 2024. The plant material was identified by Dr. Nguyen Quoc Binh, Vietnam National Museum of Nature, Vietnam Academy of Science and Technology (VAST). A voucher specimen No. GC072024 has been deposited at the Institute of Chemistry, VAST.\\u003c/p\\u003e\\n\\u003ch3\\u003eExtraction and Isolation\\u003c/h3\\u003e\\n\\u003cp\\u003eThe twigs of \\u003cem\\u003eG. cowa\\u003c/em\\u003e (5.0 kg) were dried in an oven at 45 \\u003csup\\u003eo\\u003c/sup\\u003eC for 3 days and subsequently ground into a fine powder. The powder materiel was extracted with ethanol (3 x 3 L) under ultrasonic vibration for 6 h at room temperature. The combined extract were filtred and concentrated under reduced pressure to yield a crude extract (312.4 g). The crude extract was then suspended in water and successively partitioned with \\u003cem\\u003en\\u003c/em\\u003e-hexane and ethyl acetate (EtOAc), and concentrated to afford the \\u003cem\\u003en\\u003c/em\\u003e-hexane fraction (98.1 g), the EtOAc fraction (182.4 g), and the remaining aqueous residue (31.8 g).\\u003c/p\\u003e \\u003cp\\u003eThe EtOAc fraction was separated by column chromatography (CC) over silica gel using gradient solvent systems of \\u003cem\\u003en\\u003c/em\\u003e-hexane/EtOAc (10/0 to 3/1, v/v) and dichloromethane/methanol (DCM/MeOH) (15/1 to 0/10, v/v) to provide seven main fractions (Frs. F1\\u0026ndash;F7). Fraction F3 (21.0 g) was fractioned using silica gel CC eluted with \\u003cem\\u003en\\u003c/em\\u003e-hexane/EtOAc (50/1 to 1/2, v/v) to obtain compound \\u003cb\\u003e4\\u003c/b\\u003e (12.2 mg) and compound \\u003cb\\u003e5\\u003c/b\\u003e (25.0 mg). Fraction F4 (35.9 g) was fractioned using silica gel CC eluted with \\u003cem\\u003en\\u003c/em\\u003e-hexane/acetone (30/1 to 0/10, v/v) to obtain six subfractions (Frs. F4.1-F4.6). Compound \\u003cb\\u003e1\\u003c/b\\u003e (14.6 mg) was isolated from subfraction F4.5 by repeated CC over silica gel using DCM/MeOH (40/1, v/v) as the eluent, followed by crystallisation from a mixture of DCM/MeOH to appear as pale-yellow needles. Fraction F5 (13.8 g) was chromatographed on a silica gel column eluting with DCM/MeOH (50/1 to 3/1), v/v) to give five subfractions (Frs. F5.1-F5.5). Subfraction F5.3 was first separated on a Sephadex LH-20 column using eluent of 5% DCM/MeOH and then further purified by silica gel CC eluted with DCM/MeOH (35/1, v/v) to obtaine compound \\u003cb\\u003e2\\u003c/b\\u003e (23.6 mg) as pale-yellow solid. Fraction F6 (8.6 g) was loaded onto a silica gel column eluted with DCM/MeOH (40/1\\u0026ndash;3/1, v/v) to yield five subfractions (Frs. F6.1-F6.5). Repeated chromatography of subfraction F6.2 by silica gel CC with DCM/MeOH (30/1, v/v) and further purification in a Sephadex LH-20 column using 5% DCM/MeOH to provide compound \\u003cb\\u003e3\\u003c/b\\u003e (16.2 mg) which was recrystallized from methanol as pale-yellow needles.\\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eNorrubraxanthone\\u003c/b\\u003e (\\u003cb\\u003e1\\u003c/b\\u003e): Pale yellow needles (MeOH-DCM). m.p. 216\\u0026ndash;217\\u0026deg;C. IR (KBr) \\u003cem\\u003eν\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e: 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) \\u003cem\\u003eλ\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e (log\\u003cem\\u003eɛ\\u003c/em\\u003e): 203 (4,90), 212 (4,88), 244 (4,79), 260 (4,76), 316 (4,63), 353 (4,10). \\u003csup\\u003e1\\u003c/sup\\u003eH and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR (CD\\u003csub\\u003e3\\u003c/sub\\u003eOD): see Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. HR-ESI-MS (pos.): \\u003cem\\u003em/z\\u003c/em\\u003e 397.1646 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e; calcd for C\\u003csub\\u003e23\\u003c/sub\\u003eH\\u003csub\\u003e25\\u003c/sub\\u003eO\\u003csub\\u003e6\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e, 397.1646.\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab1\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 1\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003e\\u003csup\\u003e1\\u003c/sup\\u003eH (600 MHz) and \\u003csup\\u003e13\\u003c/sup\\u003eC (125 MHz) NMR data (in CD\\u003csub\\u003e3\\u003c/sub\\u003eOD) for compounds \\u003cb\\u003e1\\u003c/b\\u003e\\u0026ndash;\\u003cb\\u003e3\\u003c/b\\u003e.\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"8\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c3\\\" colnum=\\\"3\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c4\\\" colnum=\\\"4\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c5\\\" colnum=\\\"5\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c6\\\" colnum=\\\"6\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c7\\\" colnum=\\\"7\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\".\\\" class=\\\"colspec\\\" colname=\\\"c8\\\" colnum=\\\"8\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\" morerows=\\\"1\\\" rowspan=\\\"2\\\"\\u003e \\u003cp\\u003ePosition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colspan=\\\"2\\\" nameend=\\\"c3\\\" namest=\\\"c2\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e\\u0026nbsp;\\u003c/th\\u003e \\u003cth align=\\\"left\\\" colspan=\\\"2\\\" nameend=\\\"c6\\\" namest=\\\"c5\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colspan=\\\"2\\\" nameend=\\\"c8\\\" namest=\\\"c7\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e (mult., \\u003cem\\u003eJ\\u003c/em\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003ePosition\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e (mult., \\u003cem\\u003eJ\\u003c/em\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e (mult., \\u003cem\\u003eJ\\u003c/em\\u003e)\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e164.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e161.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e161.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e6.09 (d, 1.8)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e98.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e111.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e112.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e165.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e163.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e163.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e6.16 (d, 2.4)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e93.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e6.21 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e93.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e6.26 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e93.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e158.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e4a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e156.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e156.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e6.65 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e101.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e6.68 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e103.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e6.73 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e103.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e153.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e5a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e156.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e156.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e65yt\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e154.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e157.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e158.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e142.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e144.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e144.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e129.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e137.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e137.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e8a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e112.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e8a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e112.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e112.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e183.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e183.1\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e183.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e9a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e104.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e9a\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e103.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e103.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e1ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e4.09 (d, 6.6)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e26.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e1ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e3.27 (d, 7.2)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e22.2\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e2.70 (m)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e28.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e2ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e5.25 (td, 6.6, 1.2)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e124.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e2ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e5.24 (tt, 5.4, 1.8)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e123.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e1.70 (m)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e43.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e3ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e135.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e3ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e131.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e71.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e4ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1.94 (m)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e40.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e4ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1.79 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e17.9\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e1.29 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e18.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e5ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e2.02 (m)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e16.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e5ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1.67 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e26.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e1.29 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e29.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e6ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e5.01 (m)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e125.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e1ʺ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.13 (d, 6.6)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e26.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e4.17 (d, 6.6)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e26.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e7ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e131.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e2ʺ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e5.41 (t, 6.6)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e127.8\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e5.41 (t, 6.6)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e127.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e8ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1.54 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e25.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e3ʺ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e135.3\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e135.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e9ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1.50 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e17.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e4ʺ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e4.36 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e62.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e4.37 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e61.5\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e10ʹ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1.82 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c3\\\"\\u003e \\u003cp\\u003e27.7\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e5ʺ\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e1.78 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e21.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e1.78 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e21.6\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c2\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c3\\\"\\u003e\\u0026nbsp;\\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c4\\\"\\u003e \\u003cp\\u003e7-OMe\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c5\\\"\\u003e \\u003cp\\u003e3.80 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c6\\\"\\u003e \\u003cp\\u003e61.4\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c7\\\"\\u003e \\u003cp\\u003e3.81 (s)\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\".\\\" colname=\\\"c8\\\"\\u003e \\u003cp\\u003e62.0\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eGarcinone G\\u003c/b\\u003e (\\u003cb\\u003e2\\u003c/b\\u003e): Pale yellow powder. m.p. 206\\u0026ndash;207\\u0026deg;C. IR (KBr) \\u003cem\\u003eν\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e: 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) \\u003cem\\u003eλ\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e (log\\u003cem\\u003eɛ\\u003c/em\\u003e): 210 (4,94), 243 (4.82), 260 (4.71), 316 (4.67), 358 (4.11). \\u003csup\\u003e1\\u003c/sup\\u003eH and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR (CD\\u003csub\\u003e3\\u003c/sub\\u003eOD): see Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. HR-ESI-MS (pos.): \\u003cem\\u003em/z\\u003c/em\\u003e 427.1756 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e; calcd for C\\u003csub\\u003e24\\u003c/sub\\u003eH\\u003csub\\u003e27\\u003c/sub\\u003eO\\u003csub\\u003e7\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e, 427.1757.\\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eGarcinone H\\u003c/b\\u003e (\\u003cb\\u003e3\\u003c/b\\u003e): Pale yellow needles (MeOH-DCM); m.p. 214\\u0026ndash;215\\u0026deg;C. IR (KBr) \\u003cem\\u003eν\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e: 3392, 2936, 1643, 1610, 1583, 1482, 1449, 1286, 1181, 1100, 768 cm 1. UV (MeOH) \\u003cem\\u003eλ\\u003c/em\\u003e\\u003csub\\u003emax\\u003c/sub\\u003e (log\\u003cem\\u003eɛ\\u003c/em\\u003e): 208 (4,73), 243 (4,44), 259 (4,39), 315 (4,27), 346 (3,76). \\u003csup\\u003e1\\u003c/sup\\u003eH and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR (CD\\u003csub\\u003e3\\u003c/sub\\u003eOD): see Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e. HR-ESI-MS (pos.): \\u003cem\\u003em/z\\u003c/em\\u003e 445.1866 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e; calcd for C\\u003csub\\u003e24\\u003c/sub\\u003eH\\u003csub\\u003e29\\u003c/sub\\u003eO\\u003csub\\u003e8\\u003c/sub\\u003e\\u003csup\\u003e+\\u003c/sup\\u003e, 445.1857.\\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eα\\u003c/b\\u003e \\u003cb\\u003e-Mangostin\\u003c/b\\u003e (\\u003cb\\u003e4\\u003c/b\\u003e): Yellow powder. \\u003csup\\u003e1\\u003c/sup\\u003eH NMR (CDCl\\u003csub\\u003e3\\u003c/sub\\u003e) \\u003cem\\u003eδ\\u003c/em\\u003e (ppm): 13.77 (1H, OH), 6.77 (1H, s, H-5), 6.25 (1H, s, H-4), 5.28 (2H, m, H-2ʹ, H-2ʺ), 4.07 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz, H-1ʺ), 3.80 (3H, s, OMe), 3.42 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz, H-1ʹ), 1.85 (6H, s, H-4ʹ, H-4ʺ), 1.75 (3H, s, H-5ʹ), 1.69 (3H, s, H-5ʺ).\\u003csup\\u003e13\\u003c/sup\\u003eC NMR (CDCl\\u003csub\\u003e3\\u003c/sub\\u003e) \\u003cem\\u003eδ\\u003c/em\\u003e (ppm): 182.0 (C-9), 161.5 (C-3), 160.5 (C-1), 155.7 (C-6), 155.0 (C-5a), 154.6 (C-4a), 142.6 (C-7), 137.1 (C-8), 135.2 (C-3ʹ), 132.1 (C-3ʺ), 123.2 (C-2ʺ), 121.6 (C-2ʹ), 112.1 (C-8a), 108.8 (C-2), 103.6 (C-9a), 101.6 (C-5), 93.3 (C-4), 62.0 (7-OMe), 26.6 (C-1ʺ), 25.8 (C-4ʹ, 4ʺ), 21.4 (C-1ʹ), 18.2 \\u0026amp;17.9 (C-5ʹ, 5ʺ).\\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eRubraxanthone\\u003c/b\\u003e (\\u003cb\\u003e5\\u003c/b\\u003e): Yellow powder. \\u003csup\\u003e1\\u003c/sup\\u003eH NMR (CDCl\\u003csub\\u003e3\\u003c/sub\\u003e) \\u003cem\\u003eδ\\u003c/em\\u003e (ppm): 6.63 (1H, s, H-5), 6.13 (1H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;1.8 Hz, H-4), 6.06 (1H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;1.8 Hz, H-2), 5,19 (1H, td, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.0, 0.6 Hz, H-2ʹ), 4.99 (1H, td, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6, 1.2, H-6ʹ), 4.01 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz, H-1ʹ), 3.76 (3H, s, 7-OMe), 2.03 (2H, m, H-5ʹ), 1.95 (2H, m, H-4ʹ), 1.79 (3H, s, H-10ʹ), 1.54 (3H, s, H-8ʹ), 1.50 (3H, s. H-9ʹ). \\u003csup\\u003e13\\u003c/sup\\u003eC NMR (CDCl\\u003csub\\u003e3\\u003c/sub\\u003e) \\u003cem\\u003eδ\\u003c/em\\u003e (ppm): 181.5 (C-9), 164.3 (C-3), 163.2 (C-1), 156.9 (C-4a), 156.5 (C-6), 155.3 (C-5a), 143.4 (C-7), 137.2 (C-3ʹ), 133.9 (C-7ʹ), 130.5 (C-8), 124.1 (C-6ʹ), 123.9 (C-2ʹ), 110.8 (C-8a), 102.5 (C-9a), 101.5 (C-5), 97.4 (C-2), 92.7 (C-4), 60.0 (7-OMe), 39.4 (C-4ʹ), 26.2 (C-10ʹ), 25.6 (C-1ʹ), 24.4 (C-8ʹ), 16.4 (C-9ʹ), 15.3 (C-5ʹ).\\u003c/p\\u003e \\u003cp\\u003e \\u003cb\\u003eα\\u003c/b\\u003e \\u003cb\\u003e-Glucosidase inhibition assay\\u003c/b\\u003e \\u003c/p\\u003e \\u003cp\\u003eThe \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitory assay was performed following a previously reported method with minor modifications (An et al, 2023; Hakamata et al, 2009). The test compounds were initially dissolved in dimethyl sulfoxide (DMSO) and subsequently diluted with phosphate buffer (100 mM, pH 6.8) to final concentrations of 16, 4, 1, 0.25 and 0.06 \\u0026micro;g/mL. In a 96-well microplate, each reaction well contained 40 \\u0026micro;L of phosphate buffer (100 mM, pH 6.8), 10 \\u0026micro;L of the test compound solution, and 25 \\u0026micro;L of \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase (0.4 U/mL, Sigma). The mixture was pre-incubated at 37\\u0026deg;C for 10 min, after which 25 \\u0026micro;L of \\u003cem\\u003ep\\u003c/em\\u003e-nitrophenyl-\\u003cem\\u003eα\\u003c/em\\u003e-\\u003cem\\u003eD\\u003c/em\\u003e-glucopyranoside (pNPG, 2.5 mM, Sigma) was added to initiate the reaction. Following incubation at 37\\u0026deg;C for 30 min, the reaction was terminated by the addition of 100 \\u0026micro;L of Na₂CO₃ (0.2 M). A reaction mixture without test compound served as the negative control, while acarbose was used as the positive control. All experiments were conducted in triplicate. The amount of \\u003cem\\u003ep\\u003c/em\\u003e-nitrophenol released was quantified by measuring absorbance at 410 nm using a microplate reader (BioTek, USA).\\u003c/p\\u003e \\u003cp\\u003e \\u003cem\\u003eα\\u003c/em\\u003e-Glucosidase inhibitory activity was expressed as percentage inhibition and calculated using the following equation: Inhibition (%) = [(OD control \\u0026ndash; OD sample) / OD control] x 100.\\u003c/p\\u003e \\u003cp\\u003eThe IC₅₀ value, defined as the concentration of compound required to inhibit 50% of \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase activity, was determined using TableCurve software.\\u003c/p\\u003e \\u003cdiv id=\\\"Sec6\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eStatistical analysis\\u003c/h2\\u003e \\u003cp\\u003eAll quantitative data are presented as mean\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;standard deviation (SD) from at least three independent experiments (n\\u0026thinsp;\\u0026ge;\\u0026thinsp;3). IC₅₀ values were calculated using TableCurve 2D v4 (Systat Software), in accordance with the original protocol. Differences were considered statistically significant at p\\u0026thinsp;\\u0026lt;\\u0026thinsp;0.05.\\u003c/p\\u003e \\u003c/div\\u003e\"},{\"header\":\"Results and Discussion\",\"content\":\"\\u003cdiv id=\\\"Sec8\\\" class=\\\"Section2\\\"\\u003e \\u003ch2\\u003eIsolation and structure elucidation\\u003c/h2\\u003e \\u003cp\\u003eThe ethyl acetate extract of the twigs of \\u003cem\\u003eG. cowa\\u003c/em\\u003e was separated by column chromatography to afford five tetraoxygenated xanthones, including 3 new xanthones, namely norrubraxanthone (\\u003cb\\u003e1\\u003c/b\\u003e), garcinone G (\\u003cb\\u003e2\\u003c/b\\u003e), and garcinone H (\\u003cb\\u003e3\\u003c/b\\u003e), and two known xanthones, α-mangostin (\\u003cb\\u003e4\\u003c/b\\u003e) and rubraxanthone (\\u003cb\\u003e5\\u003c/b\\u003e) (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eNorrubraxanthone (\\u003cb\\u003e1\\u003c/b\\u003e) was obtained as pale-yellow needles, m.p. 215\\u0026ndash;216 \\u003csup\\u003eo\\u003c/sup\\u003eC. The positive ion HR-ESI-MS spectrum of \\u003cb\\u003e1\\u003c/b\\u003e exhibited a protonated molecular ion peak at \\u003cem\\u003em/z\\u003c/em\\u003e 397.1646 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e, consistent with molecular fomular C\\u003csub\\u003e23\\u003c/sub\\u003eH\\u003csub\\u003e24\\u003c/sub\\u003eO\\u003csub\\u003e6\\u003c/sub\\u003e. The \\u003csup\\u003e1\\u003c/sup\\u003eH and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR spectra displayed characteristic resonances of a 1,3,6,7-tetraoxygenated xanthone, including a conjugated carbonyl carbon (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 183.3, C-9), three isolated aromatic methines [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.65 (1H, s, H-5)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 101.0 (C-5), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.16 (1H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;2.4 Hz, H-4)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 93.8 (C-4) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.09 (1H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;1.8 Hz, H-2)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 98.5 (C-2)], and six oxygenated aromatic carbons resonating at \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 142.1-165.6. The presence of a geranyl side chain was established from HSQC and HMBC data, which revealed two olefinic methines [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 5.25 (1H, td, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6, 1.2 Hz, H-2ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 124.8 (C-2ʹ) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 5.01 (1H, m, H-6ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 125.5 (C-6ʹ)], three methylene groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 4.09 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6, H-1ʹ)/ \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 26.4 (C-1ʹ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 2.02 (2H, m, H-5ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 16.6 (C-5ʹ) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.94 (2H, m, H-4ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 40.9 (C-4ʹ)], three methyl groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.82 (s, 3H, H-10ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 27.7 (C-10ʹ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.54 (s, 3H, H-8ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 25.7 (C-8ʹ) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.50 (s, 3H, H-9ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 17.7(C-9ʹ)] and two quaternary olefinic carbons [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 135.3 (C-3ʹ) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 131.8 (C-7ʹ)]. The attachment of the geranyl side chain at C-8 was confirmed by HMBC correlations from H-1ʹ to C-7 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 142.1), C-8 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 129.5) and C-8a (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 112.1) (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e). Furthermore, the spectroscopic data of compound \\u003cb\\u003e1\\u003c/b\\u003e (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e) were closely comparable to those reported for 1,3,6-trihydroxy-7-methoxy-8-(3,7-dimethyloct-2,6-dienyl)xanthone (rubraxanthone) previously isolated from \\u003cem\\u003eG. cowa\\u003c/em\\u003e and \\u003cem\\u003eG. nitida\\u003c/em\\u003e (Wahyuni et al, 2016), except for the absence of a methoxyl group. On the basis of detailed 1D and 2D NMR analyses and comparison with literature data, compound \\u003cb\\u003e1\\u003c/b\\u003e was identified as 1,3,6,7-tetrahydroxy-8-(3,7-dimethyloct-2,6-dien-1-yl)xanthone.\\u003c/p\\u003e \\u003cp\\u003e \\u003c/p\\u003e \\u003cp\\u003eGarcinone G (\\u003cb\\u003e2\\u003c/b\\u003e) was obtained as a pale-yellow powder, m.p. 206\\u0026ndash;207 \\u003csup\\u003eo\\u003c/sup\\u003eC. Its molecular formula was determined to be C\\u003csub\\u003e24\\u003c/sub\\u003eH\\u003csub\\u003e26\\u003c/sub\\u003eO\\u003csub\\u003e7\\u003c/sub\\u003e based on (+)HR-ESI-MS data, which showed a protonated molecular ion at \\u003cem\\u003em/z\\u003c/em\\u003e 427.1756 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e. The \\u003csup\\u003e1\\u003c/sup\\u003eH, and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR spectra, together with HSQC data (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e), revealed the presence of two isolated aromatic methines [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.68 (1H, s, H-5)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 103.0 (C-5), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.21 (1H, s, H-4)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 93.2 (C-4)], two olefinic methines [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 5.41 (1H, t, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz, H-2ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 127.8 (C-2ʺ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 5.24 (1H, tt, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;5.4, 1.8 Hz, H-2ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 123.9 (C-2ʹ)], one methoxy group [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 3.80 (3H, s, -OCH\\u003csub\\u003e3\\u003c/sub\\u003e)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 61.4], one oxygenated methylene [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 4.36 (2H, s, H-4ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 62.0 (C-4ʺ)] and three methyl groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.79 (3H, s, H-4ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 17.9 (C-4ʹ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.78 (3H, s, H-5ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 21.6 (C-5ʺ) and \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.67 (3H, s, H-5ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 26.0 (C-5ʹ)]. In addition, the presence of a conjugated carbonyl carbon at (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 183.1, C-9) and six oxygenated aromatic carbons resonating at \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 144.7-163.6 supported a tetraoxygenated xanthone skeleton bearing a prenyl and a hydroxylated prenyl side chain. The HMBC correlation between the methoxy protons and C-7 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 144.7) established the position of the methoxy substituent. The prenyl group was assigned to C-2 based on long-range HMBC correlations from H-1ʹ (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 3.27 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;7.2 Hz) to C-1 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 161.5), C-2 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 111.5), and C-3 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 163.6). Furthermore, the attachment of the 4-hydroxy-3-methylbut-2-en-1-yl side chain at C-8 was confirmed by HMBC cross-peaks from H-1ʺ (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 4.13 (2H, d, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz) to C-7, C-8 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 137.6) and C-8a (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 112.1) (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e). Accordingly, compound \\u003cb\\u003e2\\u003c/b\\u003e was identified as 1,3,6-trihydroxy-7-methoxy-2-(3-methylbut-2-en-1-yl)-8-(4-hydroxy-3-methylbut-2-en-1-yl)xanthone and was named garcinone G.\\u003c/p\\u003e \\u003cp\\u003eGarcinone H (\\u003cb\\u003e3\\u003c/b\\u003e) was isolated as pale-yellow needles, m.p. 214\\u0026ndash;215 \\u003csup\\u003eo\\u003c/sup\\u003eC. The (+)HR-ESI-MS spectrum of \\u003cb\\u003e3\\u003c/b\\u003e exhibited a protonated molecular ion peak at m/z 445.1866 [M\\u0026thinsp;+\\u0026thinsp;H]\\u003csup\\u003e+\\u003c/sup\\u003e, corresponding to the molecular formula C\\u003csub\\u003e24\\u003c/sub\\u003eH\\u003csub\\u003e28\\u003c/sub\\u003eO\\u003csub\\u003e8\\u003c/sub\\u003e. The \\u003csup\\u003e1\\u003c/sup\\u003eH and \\u003csup\\u003e13\\u003c/sup\\u003eC NMR data of \\u003cb\\u003e3\\u003c/b\\u003e (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab1\\\" class=\\\"InternalRef\\\"\\u003e1\\u003c/span\\u003e) showed characteristic signals of a tetraoxygenated xanthone bearing two prenyl-derived side chains, closely resembling those of compound \\u003cb\\u003e2\\u003c/b\\u003e. These included a conjugated carbonyl carbon (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 183.2, C-9), two isolated aromatic methines [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.73 (1H, s, H-5)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 103.0 (C-5), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 6.26 (1H, s, H-4)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 93.2 (C-4)], one olefinic methine [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 5.41 (1H, t, \\u003cem\\u003eJ\\u003c/em\\u003e\\u0026thinsp;=\\u0026thinsp;6.6 Hz, H-2ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 127.7 (C-2ʺ)], one methoxy group [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 3.81 (3H, s, -OCH\\u003csub\\u003e3\\u003c/sub\\u003e)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 61.0], one oxygenated methylene [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 4.37 (2H, s, H-4ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 61.5 (C-4ʺ)], three methyl groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.78 (3H, s, H-5ʺ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 21.6 (C-5ʺ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.29 (6H, s, H-4ʹ, H-5ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 18.4 (C-4ʹ), 29.0 (C-5ʹ)] and six oxygenated aromatic carbons resonating at \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 144.8-163.8. The major difference between compounds \\u003cb\\u003e2\\u003c/b\\u003e and \\u003cb\\u003e3\\u003c/b\\u003e was that the prenyl group attached at C-2 in \\u003cb\\u003e3\\u003c/b\\u003e was hydroxylated and fully saturated. This was supported by the presence of two methylene groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 2.70 (2H, m, H-1ʹ)/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 28.9 (C-1ʹ), \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.70 (2H, m, H-2')/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 43.3 (C-2ʹ)], two methyl groups [\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eH\\u003c/sub\\u003e 1.29 (6H, s, H-4', H-5')/\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 18.4 (C-4ʹ), 29.0 (C-5ʹ)] and an sp\\u003csup\\u003e3\\u003c/sup\\u003e oxygenated quaternary carbon at \\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 71.8 (C-3ʹ). Further support was provided by HMBC correlations from H-1ʹ to C-1 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 161.6), C-2 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 112.3), and C-3 (\\u003cem\\u003eδ\\u003c/em\\u003e\\u003csub\\u003eC\\u003c/sub\\u003e 163.8). All remaining spectroscopic features of compound \\u003cb\\u003e3\\u003c/b\\u003e were identical to those of compound \\u003cb\\u003e2\\u003c/b\\u003e. Accordingly, compound \\u003cb\\u003e3\\u003c/b\\u003e was identified as 1,3,6-trihydroxy-7-methoxy-2-(3-hydroxy-3-methylbut-1-yl)-8-(4-hydroxy-3-methylbut-2-en-1-yl)xanthone (Fig.\\u0026nbsp;\\u003cspan refid=\\\"Fig2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e).\\u003c/p\\u003e \\u003cp\\u003eCompounds \\u003cb\\u003e4\\u003c/b\\u003e and \\u003cb\\u003e5\\u003c/b\\u003e were identified as \\u003cem\\u003eα\\u003c/em\\u003e-mangostin (Khaw et al, 2020) and rubraxanthone (Wahyuni et al, 2016) respectively.\\u003c/p\\u003e \\u003c/div\\u003e\\n\\u003ch3\\u003eα-Glucosidase inhibition effects\\u003c/h3\\u003e\\n\\u003cp\\u003eAll isolated compounds (\\u003cb\\u003e1\\u003c/b\\u003e\\u0026ndash;\\u003cb\\u003e5\\u003c/b\\u003e) exhibited potent \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitory activity, with IC₅₀ values ranging from 0.39 to 1.62 \\u0026micro;M (Table\\u0026nbsp;\\u003cspan refid=\\\"Tab2\\\" class=\\\"InternalRef\\\"\\u003e2\\u003c/span\\u003e). These values indicate substantially stronger inhibition compared to the positive control acarbose (IC₅₀ = 263.01\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;10.92 \\u0026micro;M).\\u003c/p\\u003e \\u003cp\\u003e \\u003cdiv class=\\\"gridtable\\\"\\u003e\\u003ctable float=\\\"Yes\\\" id=\\\"Tab2\\\" border=\\\"1\\\"\\u003e \\u003ccaption language=\\\"En\\\"\\u003e \\u003cdiv class=\\\"CaptionNumber\\\"\\u003eTable 2\\u003c/div\\u003e \\u003cdiv class=\\\"CaptionContent\\\"\\u003e \\u003cp\\u003e\\u003cem\\u003eα\\u003c/em\\u003e-Glucosidase inhibition of compounds \\u003cb\\u003e1\\u003c/b\\u003e\\u0026ndash;\\u003cb\\u003e5\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/div\\u003e \\u003c/caption\\u003e \\u003ccolgroup cols=\\\"2\\\"\\u003e \\u003cdiv align=\\\"left\\\" class=\\\"colspec\\\" colname=\\\"c1\\\" colnum=\\\"1\\\"\\u003e\\u003c/div\\u003e \\u003cdiv align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" class=\\\"colspec\\\" colname=\\\"c2\\\" colnum=\\\"2\\\"\\u003e\\u003c/div\\u003e \\u003cthead\\u003e \\u003ctr\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eCompound\\u003c/p\\u003e \\u003c/th\\u003e \\u003cth align=\\\"left\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003eIC\\u003csub\\u003e50\\u003c/sub\\u003e (\\u0026micro;M)\\u003c/p\\u003e \\u003c/th\\u003e \\u003c/tr\\u003e \\u003c/thead\\u003e \\u003ctbody\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e1\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e1.62\\u0026plusmn;0.05\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e2\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.94\\u0026plusmn;0.14\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e3\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.43\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e4\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.39\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003e\\u003cb\\u003e5\\u003c/b\\u003e\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e0.56\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.03\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003ctr\\u003e \\u003ctd align=\\\"left\\\" colname=\\\"c1\\\"\\u003e \\u003cp\\u003eAcarbose\\u003c/p\\u003e \\u003c/td\\u003e \\u003ctd align=\\\"char\\\" char=\\\"\\u0026plusmn;\\\" colname=\\\"c2\\\"\\u003e \\u003cp\\u003e263.01\\u0026plusmn;10.92\\u003c/p\\u003e \\u003c/td\\u003e \\u003c/tr\\u003e \\u003c/tbody\\u003e \\u003c/colgroup\\u003e \\u003c/table\\u003e\\u003c/div\\u003e \\u003c/p\\u003e \\u003cp\\u003eAmong the tested compounds, compounds \\u003cb\\u003e3\\u003c/b\\u003e and \\u003cb\\u003e4\\u003c/b\\u003e displayed the strongest inhibitory activity, with IC₅₀ values of 0.43\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01 \\u0026micro;M and 0.39\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01 \\u0026micro;M, respectively. These findings suggest that subtle structural differences among the tetraoxygenated xanthones influence their interaction with the enzyme active site. Compounds \\u003cb\\u003e2\\u003c/b\\u003e and \\u003cb\\u003e5\\u003c/b\\u003e also showed strong inhibition, with IC₅₀ values below 1 \\u0026micro;M, whereas compound \\u003cb\\u003e1\\u003c/b\\u003e exhibited comparatively weaker activity (IC₅₀ = 1.62\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.05 \\u0026micro;M), though still markedly more potent than acarbose. The low IC₅₀ values observed for these tetraoxygenated xanthones are consistent with previous reports describing highly oxygenated xanthones from \\u003cem\\u003eGarcinia\\u003c/em\\u003e species, which have been shown to act as competitive or mixed-type α-glucosidase inhibitors (An et al, 2023, Nguyen et al, 2017; Tran et al, 2025, Yang et al, 2022).\\u003c/p\\u003e \\u003cp\\u003eOverall, these findings suggest that the twigs of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e represent a promising source of bioactive xanthones and warrant further mechanistic studies, including enzyme kinetics, molecular docking, and \\u003cem\\u003ein vivo\\u003c/em\\u003e evaluation.\\u003c/p\\u003e\"},{\"header\":\"Conclusions\",\"content\":\"\\u003cp\\u003eIn summary, a phytochemical investigation of the twigs of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e collected in Vietnam led to the isolation of five xanthone derivatives, among which three compounds (\\u003cb\\u003e1\\u003c/b\\u003e\\u0026ndash;\\u003cb\\u003e3\\u003c/b\\u003e) were identified as new natural products. Their structures were unambiguously elucidated using extensive spectroscopic analyses, including 1D and 2D NMR and HR-ESI-MS techniques. All isolated xanthones exhibited remarkably potent \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibitory activity, with IC₅₀ values in the low micromolar to submicromolar range (0.39\\u0026ndash;1.62 \\u0026micro;M), demonstrating activities several hundred times stronger than that of the reference drug acarbose. Notably, compounds \\u003cb\\u003e3\\u003c/b\\u003e and \\u003cb\\u003e4\\u003c/b\\u003e showed the most pronounced inhibitory effects, underscoring the importance of highly oxygenated xanthone frameworks in \\u003cem\\u003eα\\u003c/em\\u003e-glucosidase inhibition.\\u003c/p\\u003e \\u003cp\\u003eThese findings not only expand the chemical diversity of xanthones reported from \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e but also identify tetraoxygenated xanthones as promising lead compounds for the development of novel antidiabetic agents. Further studies focusing on enzyme inhibition mechanisms, structure-activity relationships, and \\u003cem\\u003ein vivo\\u003c/em\\u003e antidiabetic efficacy are warranted.\\u003c/p\\u003e\"},{\"header\":\"Declarations\",\"content\":\"\\u003cp\\u003e\\u003cstrong\\u003eAuthor contributions\\u0026nbsp;\\u003c/strong\\u003eNTKA, and TTTT contributed to the isolation and structure elucidation. DLP, PTT and NTT were responsible for testing and analysis of bioactivity assessments. NTKA, and TTTT worked on methods, software and prepared the manuscript. All authors approved the final manuscript and agreed to the submission.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eFunding\\u0026nbsp;\\u003c/strong\\u003eThis\\u003cstrong\\u003e\\u0026nbsp;\\u003c/strong\\u003ework was supported by the Vietnam Academy of Science and Technology (VAST04.02/25-26).\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eEthics approval\\u003c/strong\\u003e\\u003cbr\\u003e\\u0026nbsp;All experimental procedures involving plant materials were conducted in accordance with institutional, national, and international ethical standards. This study did not involve experiments with human participants or animals.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eConsent to participate\\u003c/strong\\u003e\\u003cbr\\u003e\\u0026nbsp;Not applicable.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eConsent to publish\\u003c/strong\\u003e\\u003cbr\\u003e\\u0026nbsp;Not applicable.\\u003c/p\\u003e\\n\\u003cp\\u003e\\u003cstrong\\u003eCompeting interests\\u003c/strong\\u003e\\u003cbr\\u003e\\u0026nbsp;The authors declare that they have no financial or personal conflicts of interest that could have influenced the work reported in this paper.\\u003c/p\\u003e\"},{\"header\":\"References\",\"content\":\"\\u003col\\u003e\\n\\u003cli\\u003eAn NTK, Hien NV, Thuy NT, Phuong DL, Bach HG, Tra NT, Tung NQ, Tham PT, Tai BH, Thuy TTT (2023). Garcicowanones C-E, three new hydrated-geranylated xanthones from the roots of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. ex Choisy, and their \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-glucosidase inhibition activities. Nat Prod Res 37(21):3668-3676. https://doi: 10.1080/14786419.2022.2098956.\\u003c/li\\u003e\\n\\u003cli\\u003eBui DN, Nguyen LTT, Nguyen L-TT, Ngo NTN, Tran PT, Nguyen HT, Dang LTN, Nguyen L-HD, Trinh BTD (2023). Two new antidiabetic xanthones from the twigs of \\u003cem\\u003eGarcinia oblongifolia\\u003c/em\\u003e. Nat Prod Res 37(15): 2541-2550. https://doi.org/10.1080/14786419.2022.2055016.\\u003c/li\\u003e\\n\\u003cli\\u003eDerosa G, Maffioli P (2012) \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-Glucosidase inhibitors and their use in clinical practice. Arch Med Sci 8(5):899\\u0026ndash;906. https://doi.org/10.5114/aoms.2012.31621.\\u003c/li\\u003e\\n\\u003cli\\u003eHakamata W, Kurihara M, Okuda H, Nishio T, Oku T. (2009). Design and screening strategies for \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-glucosidase inhibitors based on enzymological information. Curr Top Med Chem 9(1): 3-12. https://doi.org/10.2174/156802609787354306.\\u003c/li\\u003e\\n\\u003cli\\u003eKhaw KY, Ong YS, Goh B-H (2020). A rapid method for the retrieval of bioactive xanthone from \\u003cem\\u003eGarcinia mangostana\\u003c/em\\u003e: A case study of \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-mangostin. Prog Drug Discov Biomed Sci 3(1):1-5. https://doi.org/10.36877/pddbs.a0000072.\\u003c/li\\u003e\\n\\u003cli\\u003eLebovitz HE MD (1997). Alpha-glucosidase inhibitors. Endoc Metabol Clin North Ame 26(3):539-551. https://doi.org/10.1016/s0889-8529(05)70266-8.\\u003c/li\\u003e\\n\\u003cli\\u003eNguyen NK, Truong XA, Bui TQ, Bui DN, Nguyen HX, Tran PT, Nguyen LD (2017). Alpha-glucosidase inhibitory xanthones from the roots of \\u003cem\\u003eGarcinia fusca\\u003c/em\\u003e. Chem Biodivers 14(10): e1700232. https://doi: 10.1002/cbdv.201700232.\\u003c/li\\u003e\\n\\u003cli\\u003eNguyen TKA, Nguyen BN, Hoang TMN, Doan LP, Phan MG, Lee H, Kim DW, Lee JW, Tran TTT (2022). Six New Polyoxygenated Xanthones from \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e and Their Neuroprotective Effects on Glutamate-Mediated Hippocampal Neuronal HT22 Cell Death. Chem Biodiver 19(9): e202200376. https://doi: 10.1002/cbdv.202200376.\\u003c/li\\u003e\\n\\u003cli\\u003eOriola AO, Kar P (2024). Naturally occurring xanthones and their biological implications. Molecules 29(17):4241. https://doi.org/10.3390/molecules29174241.\\u003c/li\\u003e\\n\\u003cli\\u003ePham HH (1999). An illustrated flora of Vietnam (in vietnamese). Youth Publishing House, 450.\\u003c/li\\u003e\\n\\u003cli\\u003eRaksat A, Phukhatmuen P, Yang J, Maneerat W, Charoensup R, Andersen RJ, Wang YA, Pyne SG, Laphookhieo S (2020). Phloroglucinol benzophenones and xanthones from the leaves of \\u003cem\\u003eGarcinia cowa \\u003c/em\\u003eand their nitric oxide production and alpha-glucosidase inhibitory activities. J Nat Prod\\u003cem\\u003e \\u003c/em\\u003e83: 164\\u0026ndash;168. https://doi.org/10.1021/acs.jnatprod.9b00849.\\u003c/li\\u003e\\n\\u003cli\\u003eRahimi R, Nikfar S, Larijani B, Abdollahi M (2005) A review on the role of antioxidants in the management of diabetes and its complications. Biomed Pharmacother 59:365\\u0026ndash;373. https:// doi.org/10.1016/j.biopha.2005.07.002.\\u003c/li\\u003e\\n\\u003cli\\u003eRitthiwigrom T, Laphookhieo S, Pyne SG (2013). Chemical constituents and biological activities of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. Maejo Int J Sci Technol\\u003cem\\u003e \\u003c/em\\u003e7:212\\u0026ndash;231. https://doi.org/10.14456/ mijst.2013.18.\\u003c/li\\u003e\\n\\u003cli\\u003eRyu HW, Cho JK, Curtis-Long MJ, Yuk HJ, Kim YS, Jung S, Kim YS, Lee BW, Park KH (2011). \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-Glucosidase inhibition and antihyperglycemic activity of prenylated xanthones from \\u003cem\\u003eGarcinia mangostana\\u003c/em\\u003e. Phytochem 72(17):2148-2154. https://doi.org/ 10.1016/j.phytochem. 2011.08.007.\\u003c/li\\u003e\\n\\u003cli\\u003eSantos CMM, Freitas M, Fernandes E (2018). A comprehensive review on xanthone derivatives as \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-glucosidase inhibitors. Eur J Med Chem 157:1460-1479. https://doi.org/10.1016/j.ejmech. 2018. 07.073. \\u003c/li\\u003e\\n\\u003cli\\u003eSriyatep T, Siridechekorn I, Maneerat W, Pansanit A, Ritthiwigron T, Andersen RJ, Laphookhieo S (2015). Bioactive prenylated xanthones from the young fruits and flowers of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e. J Nat Prod 78:265\\u0026ndash;271. https://doi.org/10.1021/np5008476.\\u003c/li\\u003e\\n\\u003cli\\u003eTran QHN, Nguyen HTM, Nguyen TH, Nguyen TTL, Sichaem J, Do LTM (2025). New \\u003cem\\u003e\\u0026alpha;\\u003c/em\\u003e-glucosidase inhibitory xanthones from the fruits of \\u003cem\\u003eGarcinia schomburgkiana\\u003c/em\\u003e. Nat Prod Res 39(18): 5258-5263. https://doi.org/10.1080/14786419.2024.2367011\\u003c/li\\u003e\\n\\u003cli\\u003eYang L, Zhang D, Li JB, Zhang X, Zhou N, Zhang WY, Lu H (2022). Prenylated xanthones with alpha-glucosidase and alpha-amylase inhibitory effects from the pericarp of \\u003cem\\u003eGarcinia mangostana\\u003c/em\\u003e. J Asian Nat Prod Res 24(7):624-633. https://doi.org/10.1080/10286020.2021. 1967328.\\u003c/li\\u003e\\n\\u003cli\\u003eVan de Laar FA (2008). Alpha-glucosidase inhibitors in the early treatment of type 2 diabetes. Varc Health Risk Manag 4(6):1189-1195. https://doi.org/10.2147/VHRM.S3119.\\u003c/li\\u003e\\n\\u003cli\\u003eWahyuni FS, Shaari K, Stanslas J, Lajis NHJ, Hamidi D (2016). Cytotoxic properties and complete nuclear magnetic resonance assignment of isolated xanthones from the root of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. Pharmacogn Mag 12(1):S52-S56. https://doi.org/10.4103/0973-1296.176115.\\u003c/li\\u003e\\n\\u003c/ol\\u003e\"}],\"fulltextSource\":\"\",\"fullText\":\"\",\"funders\":[],\"hasAdminPriorityOnWorkflow\":false,\"hasManuscriptDocX\":true,\"hasOptedInToPreprint\":true,\"hasPassedJournalQc\":\"\",\"hasAnyPriority\":false,\"hideJournal\":false,\"highlight\":\"\",\"institution\":\"\",\"isAcceptedByJournal\":false,\"isAuthorSuppliedPdf\":false,\"isDeskRejected\":\"\",\"isHiddenFromSearch\":false,\"isInQc\":false,\"isInWorkflow\":false,\"isPdf\":false,\"isPdfUpToDate\":true,\"isWithdrawnOrRetracted\":false,\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"revista-brasileira-de-farmacognosia\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"rbfa\",\"sideBox\":\"Learn more about [Revista Brasileira de Farmacognosia](https://www.springer.com/journal/43450)\",\"snPcode\":\"43450\",\"submissionUrl\":\"https://www.editorialmanager.com/rbfa/default2.aspx\",\"title\":\"Revista Brasileira de Farmacognosia\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false},\"keywords\":\"Tetraoxygenated xanthone, Garcinia cowa, α-glucosidase, antidiabetic\",\"lastPublishedDoi\":\"10.21203/rs.3.rs-9035742/v1\",\"lastPublishedDoiUrl\":\"https://doi.org/10.21203/rs.3.rs-9035742/v1\",\"license\":{\"name\":\"CC BY 4.0\",\"url\":\"https://creativecommons.org/licenses/by/4.0/\"},\"manuscriptAbstract\":\"\\u003cp\\u003ePhytochemical investigation of the twigs of \\u003cem\\u003eGarcinia cowa\\u003c/em\\u003e Roxb. ex Choisy (Clusiaceae), collected in Vietnam, led to the isolation of five tetraoxygenated xanthones, including three new compounds, namely norrubraxanthone (\\u003cb\\u003e1\\u003c/b\\u003e), garcinone G (\\u003cb\\u003e2\\u003c/b\\u003e), and garcinone H (\\u003cb\\u003e3\\u003c/b\\u003e), together with two known compounds, \\u003cem\\u003eα\\u003c/em\\u003e-mangostin (\\u003cb\\u003e4\\u003c/b\\u003e) and rubraxanthone (\\u003cb\\u003e5\\u003c/b\\u003e). The structures of the new compounds were elucidated by comprehensive spectroscopic analyses, including 1D and 2D NMR and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), and by comparison with literature data. All isolated compounds were evaluated for their \\u003cem\\u003ein vitro α\\u003c/em\\u003e-glucosidase inhibitory activity. Compounds \\u003cb\\u003e1\\u003c/b\\u003e\\u0026ndash;\\u003cb\\u003e5\\u003c/b\\u003e exhibited potent inhibitory effects, with IC₅₀ values ranging from 0.39 to 1.62 \\u0026micro;M, which were significantly stronger than that of the positive control acarbose (IC₅₀ = 263.01\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;10.92 \\u0026micro;M). Among them, compounds \\u003cb\\u003e3\\u003c/b\\u003e and \\u003cb\\u003e4\\u003c/b\\u003e showed the most pronounced activity, with IC₅₀ values of 0.43\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01 and 0.39\\u0026thinsp;\\u0026plusmn;\\u0026thinsp;0.01 \\u0026micro;M, respectively.\\u003c/p\\u003e\",\"manuscriptTitle\":\"α-Glucosidase inhibitory tetraoxygenated xanthones from the twig extract of Garcinia cowa Roxb. ex Choisy ​\",\"msid\":\"\",\"msnumber\":\"\",\"nonDraftVersions\":[{\"code\":1,\"date\":\"2026-04-20 10:28:21\",\"doi\":\"10.21203/rs.3.rs-9035742/v1\",\"editorialEvents\":[{\"type\":\"communityComments\",\"content\":0},{\"type\":\"reviewerAgreed\",\"content\":\"\",\"date\":\"2026-04-13T12:02:57+00:00\",\"index\":0,\"fulltext\":\"\"},{\"type\":\"reviewersInvited\",\"content\":\"\",\"date\":\"2026-04-13T12:02:31+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorInvited\",\"content\":\"Revista Brasileira de Farmacognosia\",\"date\":\"2026-04-07T19:28:44+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"editorAssigned\",\"content\":\"\",\"date\":\"2026-03-20T13:28:54+00:00\",\"index\":\"\",\"fulltext\":\"\"},{\"type\":\"submitted\",\"content\":\"Revista Brasileira de Farmacognosia\",\"date\":\"2026-03-13T00:18:59+00:00\",\"index\":\"\",\"fulltext\":\"\"}],\"status\":\"published\",\"journal\":{\"display\":true,\"email\":\"info@researchsquare.com\",\"identity\":\"revista-brasileira-de-farmacognosia\",\"isNatureJournal\":false,\"hasQc\":true,\"allowDirectSubmit\":false,\"externalIdentity\":\"rbfa\",\"sideBox\":\"Learn more about [Revista Brasileira de Farmacognosia](https://www.springer.com/journal/43450)\",\"snPcode\":\"43450\",\"submissionUrl\":\"https://www.editorialmanager.com/rbfa/default2.aspx\",\"title\":\"Revista Brasileira de Farmacognosia\",\"twitterHandle\":\"\",\"acdcEnabled\":true,\"dfaEnabled\":true,\"editorialSystem\":\"em\",\"reportingPortfolio\":\"Springer Hybrid\",\"inReviewEnabled\":true,\"inReviewRevisionsEnabled\":false}}],\"origin\":\"\",\"ownerIdentity\":\"44ee435f-d64c-4e5d-b553-68e4578c904c\",\"owner\":[],\"postedDate\":\"April 20th, 2026\",\"published\":true,\"recentEditorialEvents\":[],\"rejectedJournal\":[],\"revision\":\"\",\"amendment\":\"\",\"status\":\"under-review\",\"subjectAreas\":[],\"tags\":[],\"updatedAt\":\"2026-04-20T10:28:21+00:00\",\"versionOfRecord\":[],\"versionCreatedAt\":\"2026-04-20 10:28:21\",\"video\":\"\",\"vorDoi\":\"\",\"vorDoiUrl\":\"\",\"workflowStages\":[]},\"version\":\"v1\",\"identity\":\"rs-9035742\",\"journalConfig\":\"researchsquare\"},\"__N_SSP\":true},\"page\":\"/article/[identity]/[[...version]]\",\"query\":{\"redirect\":\"/article/rs-9035742\",\"identity\":\"rs-9035742\",\"version\":[\"v1\"]},\"buildId\":\"XKTyCvWXoU3ODBz1xrDgd\",\"isFallback\":false,\"isExperimentalCompile\":false,\"dynamicIds\":[84888],\"gssp\":true,\"scriptLoader\":[]}","source_license":"CC-BY-4.0","license_restricted":false}