Chemical constituents in Thunbergia from Africa

Abstract

Objective: To investigate the chemical compounds from the ethanol extract with inhibitory effects against aldose reductase from Thunbergia. Method: Guided by anti-aldose reductase assay, compounds from the bioactive fraction (ethyl acetate extract) were separated and purified by various chromatographic methods including silica gel, Sephadex LH-20, and reversed-phase HPLC. Their structures were indentified based on analysis of the spectroscopic data including 1D and 2D NMR data. Result: Eight compounds were obtained and identified as 8-hydroxy-8-methyl-9-methene-cyclopentane[7, 11]-1, 4, 6-trihydroxy-tetrahydronaphthalene-12-one, named as thunbergia A (1), 3, 4-dihydro-4, 5, 8-trihydroxy-2-(3-methyl-2-butenyl)naphtha[2, 3-b]oxiren-1(2H)-one (2), 8-(β-gluco pyranosyloxy)-3, 4-dihydro-2-(3-methyl-2-butenyl)naphtha [2, 3-b] oxiren-1(2H)-one (3), galangin (4), quercetin (5), luteolin (6), 5, 6, 3', 4'-tetrahydroxy -3, 7-dimethoxy-flavone (7) and upeol (8). Conclusion: Thunbergia A was a new derivative of tetrahydronaphthalene, and compounds 2 and 3 were separated from the genus Thunbergia for the first time.