Abstract
In order to clarify the structure-activity relationship, synthesis of the titled compounds has been undertaken. The acid-cleavage of 14α, 15α-epoxyisobufadienolide (I) followed by oxidation with chromium trioxide gave the 14β-hydroxy-15-ketone (III). The ring opening of the β-epoxide (IV) and subsequent epimerization at C-14 resulted in formation of 15-oxo-14β-isobufadienolide (VI). Upon treatment with N-bromosuccinimide and then with lithium chloride or sodium iodide 14β, 17α- and 14α, 17β-isobufadienolides (IX and XIII) were led to Δ16, Δ14, 16 and Δ16-14β, 15β-epoxy derivatives (X, XV and XVI), respectively.
