The syntheses of two new bufadienolides with ring-o oxygen substituants in abnormal configurations have been summarised. Sodium borohydride reduction of 3β-acetoxy-16-oxo-14β,15β epoxy-5β-bufa-20,22-dienolide (3) provided a readily separable (1:1) mixture of 16α-deacetylcinobufagin (1a) and its previously known 16β-epimer. Also, 14-epi-bufotalin acetate (2a) was obtained by a sequence in which 14-dehydrobufotalin acetate (7) was epoxidised with m-perchlorobenzoic acid to give the diacetate (5a), selective alkaline hydrolysis of which gave the monoacetate (5b), which was then oxidised with chromium trioxide to give the ketone (8); reduction of (8) with chromium(II) acetate gave the alcohol (9), which was then reduced at the carbonyl to the diol (2b) with Urushibara nickel, and finally acetylated to afford the synthetic objective (2a).
|Original language||English (US)|
|Number of pages||5|
|Journal||Journal of the Chemical Society, Perkin Transactions 1|
|State||Published - 1988|
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