Synthesis of 3 alpha- and 3 beta-dimers from selected bile acids

New dimers of bile acids have been synthesized by linking the hydroxyl groups on C3 of the steroid skeleton with a spacer via the formation of ester or ether bonds. 3 alpha-Dimers of lithocholic acid and cholic acid were prepared by forming ester linkages between the C3 hydroxyl group and dicarboxylic acids of different lengths, i.e., suberoyl chloride (eight carbons) and sebacoyl chloride (ten carbons). These dimers were obtained in three steps with an overall yield of about 70%. Regioselective hydrolysis of the methyl ester protecting groups on the bile acids was carried out successfully under mild alkaline conditions (aqueous lithium hydroxide with tetrahydrofuran). A 3 beta-dimer of lithocholic acid has also been synthesized by linking the C3 positions of two bile acids with diethylene glycol by the formation of ether linkages. The carboxylic acid groups of the bile acid dimer can be liberated by the removal of the methyl ester protecting groups.