Two glycosides of a novel dammarane alcohol from Gynostemma pentaphyllum.
Abstract
From the aerial parts of Gynostemma pentaphyllum MAKINO (Cucurbitaceae), two glycosides were isolated, namely gynosaponin TN-1 (III), C36H62O9·3/2H2O, mp 168-173°, [α]D+34.5°and gynosaponin TN-2 (IV), C42H72O13·1/2H2O, mp 236-240°, [α]D+11.6°. On acid hydrolysis, gynosaponin TN-1 (III) yielded glucose as its sugar moiety and 2α-hydroxypanaxadiol (II), C30H52O4 as an artificial genin, while gynosaponin TN-2 (IV) afforded rutinose and II. The structure of II was elucidated to be 20, 25-epoxydammarane-2α, 3β, 12β-triol on the basis of its mass spectrum, molecular optical rotation and nuclear magnetic resonance (NMR) spectra (1H, 13C) in comparison with those of panaxadiol (I). Carbon 13 NMR spectra of III and IV indicated that their aglycone moiety has a (20S)-dammar-24-en-20-ol partial structure. Their chemical structures were established as (20S)-dammar-24-ene-2α, 3β, 12β, 20-tetraol 20-O-β-D-glucopyranoside (III) and (20S)-dammar-24-ene-2α, 3β, 12β, 20-tetraol 20-O-α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranoside (IV).