The pregnane glycosides of the climbing form of Sarcostemma viminale (L.) R

Abstract

AbstractThe dried twigs and stems of Sarcostemma viminale (the climbing shrub form from South Rhodesia) contain about 1% phenolic and a similar amount of glycosidic compounds derived from 2‐deoxysugars; only traces of cardenolides are present. After mild acidic hydrolysis 5 sugars could be detected and subsequently isolated in pure form. Three of them (d‐cymarose, d‐digitoxose and lilacinobiose) were obtained crystalline, the two others (d‐oleandrose and viminose) in amorphous form. Viminose is a new sugar, a disaccharide which contains d‐thevetose, and d‐Digitoxose at the reducing end [30 b].The mixture of aglycones, obtained after mild acidic hydrolysis, contained mainly five components (F, G, H. J and K), all of which could be isolated in pure form. F, G and J were crystalline. F was identified as metaplexigenin (1), J as mono‐O‐acetyl‐mono‐O‐benzoyl‐sarcostin (5) and K as 12,20‐di‐O‐benzoyl‐sarcostin (6). G and H are new compounds whose structures (G = 12‐O‐benzoyl‐deacetyl‐metaplexigenin (2), H = di‐O‐benzoyl‐viminolone (3)) are deduced in the following paper. After alkaline hydrolysis of the aglycone mixture, sarcostin, deacetylmetaplexigenin and small amounts of lineolon could be dedected by paper‐ and thinlayerchromatography.The two pregnane derivatives EA‐42 and EA‐43 described by Abisch et al. [21] could be identified with 3, 20‐di‐O‐benzoyl‐utendin and 3, 20‐di‐O‐benzoyl‐sarcostin, respectively.In the NMR.‐spectra of sarcostin and of many (not all) of its derivatives a strong signal (mostly a singlet corresponding to ca. 3 protons at ca. δ = 2 ppm) is present, which cannot be explained with the suggested structures. The cause of this extra signal could not be elucidated.