Studies on the constituents of Asclepiadaceae plants. Part 67. Further studies on glycosides with a novel sugar chain containing a pair of optically isomeric sugars, D- and L-cymarose, from Cynanchum africanum

Abstract

Two new glycosides named cynafoside-C (3) and -D (4) were isolated from Cynanchum africanum R. BR. (Asclepiadaceae), and their structures were deduced on the basis of spectral and chemical evidence. The absolute configurations of cymarose, oleandrose, and digitoxose included in compounds (3) and (4) were each determined by h.p.l.c. analysis of their carbamoyl derivatives on a chiral column after acidic hydrolysis of the glycosides. A unique feature is that cynafoside-C (3), as well as cynafoside-A (1) and B (2), contains a pair of optically isomeric sugars, D-and L-cymarose, in the sugar chain.