Bark extractives of Catalpa bungei: isolation, purification and structural elucidation of triterpene, phytosterol and flavonoid derivatives

초록

Extractives of tree barks have long been considered as a rich source of novel bioactive secondary metabolites, which are by far not well-explored. In the current work, bark extracts of Catalpa bungei were investigated for the first time and five extractives were isolated and purified, including a new triterpene saponin derivative, namely 3-O-beta-D-glucuronopyranosyl-6 '-methyl-21-O-cis-caffeoyl machaerinic acid (4), two known flavonoids [(+)-gallocatechin (1) and isoquercitrin-6 ''-gallate (2)], a known oleanane-type triterpene [machaerinic acid (3)] and a known phytosterol [stigmasterol (5)]. Chemical structural elucidation of extractives 1-5 was carried out mainly on the basis of their physicochemical and spectroscopic (IR, NMR, MS) evidences and analysis, as well as by detailed comparison of the analytical evidence with those in the literature. To the best of the authors' knowledge, this is the first time to find the occurrence of extractives 1-5 in the tree of C. bungei. It is noteworthy that the five constituents have never previously been reported in any species of Catalpa genus. Compound 4, a previously undescribed triterpene saponin derivative, was isolated and elucidated in this work for the first time.

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