Complement-Inhibiting Constituents of Bridelia ferruginea Stem Bark

A bioassay-guided fractionation of an 80% acetone extract from BRIDELIA FERRUGINEA stem bark showing a dose-dependent inhibitory effect towards both the classical and the alternative pathways of the complement system resulted 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'-trimethyl ether ( 6; new compound) named ferrugin, myricetin 3,3',4',5'-tetramethyl ether ( 7), myricetin ( 8), and quercetin 3- O-glucoside ( 9) as the active constituents. Especially the biflavanol 1 and the caffeoyl esters of quinic acid 2 and 3 showed a strong inhibitory effect (IC (50) < 10 microM) on the classical pathway, compared to rosmarinic acid. Also on the alternative pathway, the biflavanol 1, the quinic acid derivatives 2 and 3, and some of the 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.