7β,8β-Epoxycardenolide glycosides of Asclepias eriocarpa
Abstract
The identity of eriocarpin with desglucosyrioside (1) has been established by comparison of their triacetates. 13C and 1H N.m.r. spectra show that the conversion of labriformidin into desglucosyrioside involves solely the reduction of a 3-keto-function in the carbohydrate portion (B) which is identical (in structure and stereochemistry) with that in uscharidin (7). Structures are proposed for labriformidin and labriformin. 13C N.m.r. data establish the β-configuration of the 7,8-epoxide in labriformidin, desglucosyrioside, and in the 5β-cardenolide sarverogenin (11).