Dauresorcinols A and B, Two Pairs of Merosesquiterpenoid Enantiomers with New Carbon Skeletons from Rhododendron dauricum

Five pairs of new merosesquiterpenoid enantiomers, named dauresorcinols A−E ( 1 − 5 ), were isolated from the leaves of Rhododendron dauricum . Their structures were elucidated by comprehensive spectroscopic data analysis, quantum chemical calculations, Rh 2 (OCOCF 3 ) 4 -induced ECD, and single-crystal X-ray diffraction analysis. Dauresorcinols A ( 1 ) and B ( 2 ) possess two new merosesquiterpene skeletons bearing an unprecedented 2,6,7,10,14-pentamethyl-11-oxatetracyclo[8.8.0.0 2,7 .0 12,17 ]octadecane and a caged 15-isohexyl-1,5,15-trimethyl-2,10-dioxatetracyclo[7.4.1.1 11,14 .0 3,8 ]pentadecane motif, respectively. Plausible biosynthetic pathways of 1 − 5 are proposed involving key oxa-electrocyclization and Wagner−Meerwein rearrangement reactions. (+)/(−)- 1 and 3 − 5 showed potent α-glucosidase inhibitory activity, 3 to 22 times stronger than acarbose, an antidiabetic drug targeting α-glucosidase. Docking results provide a basis to design and develop merosesquiterpenoids as potent α-glycosidase inhibitors.