Synthesis of 5α-cinobufagin

Abstract

Cinobufagin (I) and cinobufotalin (IV) isolated from the Chinese toad venom preparation Ch'an Su were used as starting points for synthesis of 5α-cinobufagin (III) via the 3-oxo-4-ene derivative VII. Lithium borohydride reduction of ketone VII afforded 5α-cinobufagin (III) accompanied by 3-epicinobufagin (IX). Ring A diene II, was obtained as one of the dichlorodicyanobenzoquinone oxidation products of 3-oxocinobufagin (V).