New procedures for selectively protected cholic acid derivatives. Regioselective protection of the 12α-OH group, and t-butyl esterification of the carboxyl group

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Abstract
Effective procedures have been developed for the preparation of various selectively protected cholic acid derivatives. Treatment of cholic acid or methyl cholate with trifluoroacetic anhydride in THF, followed by partial deacylation under acidic conditions, leads to the 12α-trifluoroacetates (10a) and (10m), respectively. Trifluoroacetic anhydride may also be used as a condensing agent in the synthesis of t-butyl cholates. Particularly notable is the preparation of the ester (10b), which incorporates both these developments and is arguably the most efficient method yet for differentiating between positions 7 and 12 in the cholic acid nucleus.