抄録
Convallasaponin-C (I) from Convallaria keisukei MIQ. was completely hydrolyzed affording isorhodeasapogenin (25D-5β-spirostane-1β, 3β-diol), L-arabinose and L-rhamnose. The molar ratio of these sugars was found to be 1 : 2 on the basis of separating their tetraazoates prepared from the sugar moiety obtained after hydrolysis. This ratio was also indicated by gas chromatography (Fig.1). Prosapogenin-I and prosapogenin-II were obtained by the partial hydrolysis of I. The former was further hydrolyzed into isorhodeasapogenin and L-arabinose which were also obtained with the additional sugar component, L-rhamnose, from prosapogenin-II. Hydrolysis of the permethylate (II), fully methylated I, afforded isorhodeasapogenin monomethylate (III) which was oxidized to C3-keto derivative (IV) by chromium trioxide in acetic acid. Hydrolysis of II afforded three partially methylated sugars, 3, 4-di-O-methyl-L-arabopyranose, 2, 4-di-O-methyl-L-rhamnopyranose and 2, 3, 4-tri-O-methyl-L-rhamnopyranose in a molar ratio of 1 : 1 : 1(Fig.4). Analysis of the molecular rotation differences (Table IV) between isorhodeasapogenin, prosapogenin-I, -II and I would indicate that the glycosidic linkages in these substances are all in the α-form. Consequently the structure of convallasaponin-C might reasonably be formulated as isorhodeasapogenin (3)α-L-rhamnopyranosyl (1→3 rham.)-α-L-rhamnopyranosyl (1→2 arab.)-α-L-arabopyranoside (Chart 2).
