A facile and efficient synthesis of the carboxyl-linked glucosides of bile acids is described. Direct esterification of unprotected bile acids with 2,3,4,6-tetra-O-benzyl-D-glucopyranose in pyridine in the presence of 2-chloro-1,3,5-trinitrobenzene as a coupling agent afforded a mixture of the alpha- and beta-anomers (ca. 1:3) of the 1-O-acyl-D-glucoside benzyl ethers of bile acids, which was separated effectively on a C18 reversed-phase chromatography column (isolated yields of alpha- and beta-anomers are 4-9% and 12-19%, respectively). Subsequent hydrogenolysis of the alpha- and beta-acyl glucoside benzyl ethers on a 10% Pd-C catalyst in acetic acid/methanol/EtOAc (1:2:2, by vol) at 35 degrees C under atmospheric pressure gave the corresponding free esters in good yields (79-89%). Chemical specificities such as facile hydrolysis and transesterification of the acyl glucosides in various solvents were also discussed.

Key WordsGas chromatography-mass spectrometry Bile acids and glycosylated bile acids Ca rboxyl-lin ked g I ucosides Ester glucosides and fl anomers SummaryThis paper deals for the first time with a direct method for analysis of the ~ and fl anomers of bile acid esters of glucose by capillary gas chromatography (CGC) without the need for a hydrolytic step. The bile acid esters were derivatized to their trimethylsilyl (TMS) ethers, which in turn were chromatographed on a short (7 m) metal capillary column chemically coated with a thin (0.15 gm) film of thermostable, non-polar polydimethylsiloxane. Satisfactory CGC separation of the isomeric bile acid esters was achieved on the column; the fl anomers eluted before the corresponding ~ isomers. Particularly noteworthy is that the ~ anomers are partially isomerized to the corresponding fl anomers, and that both anomers are partially decomposed during CGC analysis, demonstrating the chemical specificity and thermal instability of the bile acid esters.