Flavonoids From Caragana Leucophloea And Their Antimicrobial And Antioxidant Activities

Caragana leucophloea Pojark. belongs to the genus Caragana, tribe Galegeae, subfamily Faboideae, family Leguminosae. It mainly distributes in the Provinces of Xinjiang, Gansu and Mongolia. The crude ethanol extract from the aerial parts of C. leucophloea along with its fractions with different polarities were prepared and evaluated for their antimicrobial activity and antioxidant activity. The antimicrobial compounds were separated from the ethyl acetate fraction based on bioassay-guided fractionation. The main results are as follows.The results showed that the crude ethanol extract exhibited significant antifungal activity. Of them, ethyl acetate fraction was found to have the strongest antifungal and antioxidant activity which suggested that the antifungal and antioxidant components with their moderate polarity mainly existed in the ethyl acetate fraction.The ethyl acetate fraction was found to have a high value of flavonoid content, so it was further purified with HSCCC in order to prepare crude flavonoid fraction. Eight fractions were collected according to the elution profile, the highest flavonoid content was determined in the peak 4 fraction (20.51%) which was 5.26-fold of the flavonoid content of the crude extract. After optimization of separation conditions, one peak was obtained and identified as 3-O-methylkaempferoI with its purity as 96.78%.By bioassay-guided fractionation, three compounds were isolated and purified by column chromatography on silica gel, sephadex LH-20 and recrystallization from ethyl acetate fraction. Based on the spectrum analysis of their 1H-NMR,13C-NMR data, the compounds were identified as 3-O-methylkaempferol (1),3-O-methylquercetin (2), and quercetin (3).The compounds were evaluated for MIC and IC50 values by micro-dilution assay for the antimicrobial activity. Compounds 1,2 and 3 showed stronger inhibitory activity against Ralstonia solanacearum with their MIC values of 12.5μg/mL,25μg/mL and 7.42μg/mL, IC50 values of 7.42μg/mL,12.10μg/mL and 12.29μg/mL. Compounds 1,2 and 3 also exhibited inhibitory activities on the spore germination of Magnaporthe oryzae, with IC50 values of 56.56μg/mL, 76.61μg/mL and 49.80μg/mL.The antioxidant activity of the compounds was measured by DPPH radical scavenging assay andβ- carotene/linoleic acid system assay. The results showed that the compounds 3 and 2 exhibited stronger antioxidant activity to scavenge DPPH radical with the IC50 values of 13.64μg/mL and 12.10μg/mL; at the same time, they also exhibited batter antioxidant activity to inhibitedβ- carotene bleaching with the IC50 values of 9.87μg/mL and 10.26μg/mL.This is the first time to study the flavonoids ant their antimicrobial and anoxidant activities from C. leucophloea. The results could provide additional data for future development and utilization of C. leucophloea in the future.