Potential bile acid metabolites. 13. Improved routes to 3 beta, 6 beta- and 3 beta, 6 alpha-dihydroxy-5 beta-cholanoic acids

New synthetic routes to three possible stereoisomers of hyodeoxycholic (3 alpha, 6 alpha-dihydroxy-5 beta-cholanic) acid are described. The principal reactions involved were inversion at C-3 of 3 alpha-hydroxy-6-oxo derivatives with diethyl azodicarboxylate-triphenylphosphine-formic acid and with N,N-dimethylformamide, without allomerization to the more stable 5 alpha form. On the basis of physical and chromatographic data, previously reported 3 beta, 6 alpha-dihydroxy-5 beta-cholanic acid and its methyl ester are shown to be C-3 epimeric mixtures. The 13C nuclear magnetic resonance spectra were of key importance in characterizing the stereoisomers and estimating their purity.