Cardenolide glycosides of the asclepiadaceae. New glycosides from asclepias fruticosa and the stereochemistry of uscharin, voruscharin and calotoxin

Abstract

Eight new cardenolide glycosides, 19-deoxyuscharin (1b), 4′β-hydroxygomphoside (1k), 3′-didehydrogomphoside (1d), 3′-epigomphoside (1e), 3′-epiafroside (2e), 3′-epigomphoside 3′-acetate (1f), 3′-didehydroafroside (2d), and 3′-epiafroside 3′-acetate (2f), have been isolated from Asclepias fruticosa R. Br. The structures of all new compounds were established by spectral comparisons with known compounds. The chirality at C-3′ of uscharin (3b), voruscharin, and 19-deoxyuscharin (1b) is proposed to be S. By comparison with 4′β-hydroxygomphoside (1k), the β configuration of the 4′-hydroxy group of calotoxin (3k)(from Calotropis procera) has been established.