Ring A-seco limonoids and flavonoids from the Kenyan Vepris uguenensis Engl. and their antioxidant activity.

Two A-seco-limonoids, accorded the trivial names, uguenensene and uguenensone and a C-7 prenylated flavonoid, uguenenprenol were isolated from Vepris uguenensis (Rutaceae). In addition, 11 known compounds, niloticin, chisocheton A, kihadalactone A, limonyl acetate, methyl uguenenoate, 7-O-methylaromadenrin, flindersiamine, 8α,11-elemodiol, tricoccin S₁₃ acetate, skimmianine, and lupeol were isolated. The structures of the compounds were elucidated and characterized by spectroscopic analyses (NMR, GC-MS and IR). Antioxidant activity of the isolated compounds showed that uguenenprenol and 7-O-methylaromadenrin are good antioxidant agents. Significantly high antioxidant activity was also exhibited by 8α,11-elemodiol, which was 72% at 250 μg mL⁻¹ and 57% at 15.62 μg mL⁻¹ when tested with the deoxyribose method. The two liminoids fit nicely into the biosynthetic pathway from niloticin to methyl uguenenoate.