Synthesis, characterisation and biological activities of homoisoflavonoids.
Fifteen homoisoflavonoids (3-17) were synthesised using the base-catalysed aldol condensation, thirteen of which were of the 3-benzylidene-4-chromanone type and the remaining two of the 3-benzyl-4-chromanone type. The substitution patterns of the homoisoflavonoids were varied by keeping the A-ring unsubstituted whilst changing the substituent’s on the 3' and 4' positions of the B-ring. Methoxy, hydroxy, chloro, fluoro and nitro groups were inserted on the B-ring of the homoisoflavonoids. All homoisoflavonoids were characterised by NMR (1D and 2D), IR, UV spectroscopy and GC-MS. The crystal structures were obtained for seven of the homoisoflavonoids. The homoisoflavonoids (3-17) were tested for their antibacterial activity against ten gram-positive and six gram-negative bacterial strains using the method of disc diffusion. Five compounds showed moderate antibacterial activity whilst compound 14 showed good antibacterial activity against the gram positive bacteria. The hydroxylated compounds were tested for their antioxidant activity using the DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging method as well as the FRAP (ferric reducing antioxidant power) method. Compound 15 showed good antioxidant activity, comparable to that of ascorbic acid, due to the presence of a catechol system within the molecule.