Differential behavior of (25R)-5,6-epoxyspirostan-22 alpha-O-3 beta-ol and (25R)-5,6-epoxyspirostan-22 alpha-O-3 beta,4 beta-diol toward Dowex

Abstract

The acid-catalyzed hydrolytic cleavage of the 5,6-epoxyspirostane derivatives by the cation exchange resin Dowel 50W X8 has been exploited with the goal of developing synthetic protocols toward 3,4,5,6-polyhydroxyspirostane analogs that can serve as intermediates to potential biologically active compounds. Whereas the diastereomers (25R)-5 alpha,6 alpha-epoxyspirostan-22 alpha-O-3 beta-ol and (25R)-5 beta,6 beta-epoxyspirostan-22 alpha-O-3 beta-ol yield two products, (25R)-6 beta-methoxyspirostan-22 alpha-O-3 beta,5 alpha-diol and (25R)-spirostan-22 alpha-O-3 beta,5 alpha,6 beta-triol on Dowex treatment in water-methanol, the alpha- and beta-diastereomers of the 5,6-epoxy derivative of 3 beta,4 beta-diol provide a single product, (25R)-3 beta,6 beta-dihydroxy-5 alpha-spirostan-4-one, in good yields. The structures of these products have been confirmed using H-1 NMR, C-13 NMR, and H-1-H-1 J-correlated spectroscopies. Multifunctional product formation suggests tremendous utility of Dowex in steroid synthesis. The product formation has been rationalized on the basis of differential conformational constraints of the A/B rings of the different epoxides in directing the reaction course. The reaction shows an interesting example of stereoelectronic stereoelectronic effect of a single hydroxy group in discriminating solvent participation.