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.