Bufadienolide glycosides of the Crassulaceae. Structure and stereochemistry of orbicusides A—C, novel toxic metabolites of Cotyledon orbiculata

Abstract

Three new bufadienolide glycosides, orbicusides A—C, in addition to the known tyledoside C, have been identified as the toxic principles of Cotyledon orbiculata L. var. orbiculata. The structures (3), (5), and (6) for orbicusides A—C, respectively, with three ether bridges between the 4,6-dideoxyhexose moiety and the bufadienolide aglycone, were deduced from a detailed ¹H and ¹³C n.m.r. study.