[Study on antioxidant chemical constituents of Lonicera japonica leaves].

Guided by the antioxidant activity, the EtOAc-soluble and n-butanol-soluble fractions of the 50% methanol extract of Lonicera japonica leaves were isolated and purified by various chromatorgraphic methods, and the structures were identified by spectral analysis and comparison to the data reported in literature. As a result, nine compounds were obtained and identified as 5-O-caffeoylquinicacid (1), chlorogenicacid (2), 4-O-caffeoylquinicacid (3), luteolin-7-O-[α-L-arabinopyranosyl-(1 --> 6)] -β-D-glucopyranoside (4), luteoloside (5), 3,4-di-O-caffeoylquinic acid (6), 3,5-di-O-caffeoylquinic acid (7), 4, 5-di-O-caffeoylquinic acid (8) and luteolin (9). The antioxidant activity of the nine compounds were determined by using DPPH free radical scavenging method, and ascorbic acid was used as a positive control. Their antioxidant activities from high to low were 5 > 9 > 2 > 8 > 7 > 6 > 1 > 3 > 4. Among them, luteoloside (5) had the strongest antioxidant activity with an IC50 of 0.018 18 g x L(-1), and luteolin (IC50 0.023 6 g x L(-1)) and chlorogenicacid (IC50 0.035 17 g x L(-1)) ranks No. 2 and 3. Furthermore, the antioxidant activity of luteoloside and luteolin were stronger than that of ascorbic acid (IC50 0.027 54 g x L(-1)). These results gave a basis for the further study and utilization of L. japonica leaves.