ABSTRACT
Objective: To study the flavonoids of the stems and leaves of male Trichosanthes kirilowii and to make a primary research on the structure activity relationship between flavonoids and their DPPH-scavenging capacity. Methods: Flavonoids from the stems and leaves of male T. kirilowii were separated by chromatographic techniques, such as polyamide resin, high-speed countercurrent chromatography and high performance liquid chromatography. According to the chemical properties and spectral analysis, the chemical structures of the compounds were identified. And we determined the antioxidant ability in vitro of seven flavonoids by DPPH methods. Results: Seven flavonoids were isolated from the stems and leaves of male T. kirilowii. They were luteolin (1), chrysoeriol (2), luteolin-7-O-β-D-glucoside (3), chrysoeriol-7-O-β-D-glucoside (4), apigenin-7-O-β-D-glucoside (5), diosmetin-7-O-β-D-glucoside (6), and quercetin-3-O-β-glucoside (7). Under the present experimental condition, the order of their DPPH-scavenging capacities was 1 > 3 > 7 > 2 > 4> 6 > 5. Conclusion: Compounds 1, 2, 6, and 7 are isolated from this part of male T. kirilowii for the first time. DPPH-scavenging capacities of the compounds 1, 3, and 7 are much stronger than others, but they all have 3',4' two adjacent hydroxide groups in B ring on the view of structure. DPPH-scavenging capacities of compounds 4 and 6 are much weaker than compound 3, but the former have 3' or 4' hydroxyl methylation in the structure. DPPH-scavenging capacity will also decrease if there is a 7 hydroxyl glycosylation in ring A by comparing compound 1 and 3. We speculate that it is caused by the increase of the steric hindrance.