Complement-Inhibiting Constituents of Bridelia ferruginea Stem Bark

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Abstract
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 (IC50 < 10 µM) 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.

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