Phosphorus-nitrogen compounds: Part 69. Unsymmetrical Dispiro(N/N)cyclotriphosphazenes Containing Different Pendant Arms: Syntheses, Characterization, Stereogenism, Photophysical and Bioactivity Studies

In this research, the starting compounds tetrachloromonospirocyclotriphosphazenes, (BzSpiro-5)R 1 (N 3 P 3 )Cl 4 [Bz: Benzyl; R 1 Me ( 1 ) and R 1 Et ( 2 )], were synthesized from the reactions of hexachlorocyclotriphosphazene, N 3 P 3 Cl 6 ( HCCP , trimer) with N/N-donor type benzyldiamines. Both phosphazenes were reacted with 9-ethyl-N-methyl-3-carbazolyldiamines ( 3 and 4 ) to form dichloro trans/cis N/N-dispirocyclotriphosphazenes, [(BzSpiro-5)R 1 (N 3 P 3 )(CzSpiro-n)R 2 ]Cl 2 (Cz: Carbazolyl; R 1 , R 2 Me or Et; n= 5 or 6; ( 5a - 8a and 5b - 8b ), containing unsymmetrical diamino precursors. The structure of the cis- 5b was clarified by single crystal X-ray crystallography. The space group of the chiral cis- 5b isomer is P -1, which is centrosymmetric, and both enantiomers must be present in the unit cell. Since the absolute configuration of an enantiomer is found as SR' according to the X-ray crystallography, the other must be RS'. The chiralities of the compounds were also confirmed by 31 P NMR spectroscopy recorded upon addition of chiral solvating agent [(S)-(+)-2,2,2-trifluoro-1-(9’-anthryl)ethanol; CSA] (for 5a , 5b and 8b ) and the circular dichroism (CD) (for 5a , 5b , 6a and 6b ) spectra. All N/N-dispirocyclotriphosphazenes ( 5a - 8b ) bearing carbazole units exhibited a fluorescence profile with a lifetime of about 4.9-6.5 ns and a quantum yield in the range of 0.11-0.20. On the other hand, P. aeruginosa was sensitive to compounds 5b , 7a , 8a and 8b , while E. coli was sensitive to most of the phosphazenes. The cytotoxic activities of phosphazenes against Vero cells (healthy) and MDA-MB-231 breast cancer cells were determined. In addition, compounds 5a and 5b appear to have very high antioxidant activity with respect to radical scavenging activities of 55.1% and 68.3%, respectively.