Complement-inhibiting constituents of Bridelia ferruginea stem bark

A bioassay-guided fractionation of an 80 % acetone extract from Bridelia fe rruginea stem bark showing a dose-dependent inhibitory effect towards both the classical and the alternative pathways of the complement system resulte d in the isolation of a biflavanol (gallocatechin-(4'-O-7)-epigallocatechin ) (1), 3,5-dicaffeoylquinic acid (2), 1,3,4,5-tetracaffeoylquinic acid (3), and a series of 3-methoxyflavone derivatives, including quercetin 3-methyl ether (4), quercetin 3,7,3',4'-tetramethyl ether (5), myricetin 3',4',5'-t rimethyl ether (6; new compound) named ferrugin, myricetin 3,3',4',5'-tetra methyl ether (7), myricetin (8), and quercetin 3-O-glucoside (9) as the act ive constituents. Especially the biflavanol 1 and the caffeoyl esters of qu inic acid 2 and 3 showed a strong inhibitory effect (IC50 < 10 mu M) on the classical pathway, compared to rosmarinic acid. Also on the alternative pa thway, the biflavanol 1, the quinic acid derivatives 2 and 3, and some of t he 3-methoxyflavones 5, 7 and 8 were more active than rosmarinic acid. The quinic acid derivatives were shown to be inhibitors of the C1 component and the terminal route of the complement system.