Novel Acylated Saponins from Montbretia (Crocosmia crocosmiiflora). II. : The Structures of Crocosmiosides C, D, E, F, G and I

Abstract

Six novel triterpenoid saponins, named crocosmiodsides C, D, E, F, G, and I, were isolated from the corms of montbretia (Crocosmia crocosmiiflora N.E.Br., Iridaceae). The structures of these saponins were determined on the basis of spectral and chemical evidence. They are 3, 28-di-O-glycosides of polygalacic acid, carrying hydroxylated palmitic acid derivatives at the C-4 position of the β-D-fucopyranosyl moiety. Namely, crocosmiosides C (1), D (2), E (3), F (4), and G (5) bear 3-O-[α-L-arabinopyranosyl-(1→ 6)-β-D-glucopyranosyl]-28-O-{2-O-[β-D-apio-D-furanosyl-(1→4)-β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl]-3-O-(β-D-glucopyranosyl)-β-D-fucopyranosyl}-polygalacic acid as as common structural unit of the desacylsaponin moiety, while the structures of the acyl moiety of crocosmiosides C (1), D (2), E (3), F (4), and G (5) are 9-oxo-16-hydroxy-2-β-D-xylopyranosyloxyhexadecanoic acid, 9, 16-dihydroxy-2-β-D-xylopyranosyloxyhexadecanoic acid, 2, 9, 16-trihydroxyhexadecanoic acid, 2, 9-dihydroxy-16-α-L-rhamnopyranosyloxyhexadecanoic acid, and 9-oxo-16-α-L-rhamnopyranosyloxy-2-β-D-xylopyranosyloxyhexadecanoic acid, respectively. In addition, the structure of crocosmioside I (6) which has a different desacylsaponin moiety was elucidated as 3-O-[α-L-arabinopyranosyl-(1→6)-β-D-glucopyranosyl]-28-O-{2-O-[β-D-xylopyranosyl-(1→4)-α-L-rhamnopyranosyl]-3-O-(β-D-glucopyranosyl)-4-O-(2, 9-dihydroxy-16-α-L-rhamnopyranosyloxyhexadecanoyl)-β-D-fucopyranosyl}-polygalacic acid.