Derivatization of bile acids with taurine for analysis by fast atom bombardment mass spectrometry with collision-induced fragmentation

When analyzed by fast atom bombardment mass spectrometry, taurine- conjugated bile acids give intense [M-H]^- pseudomolecular ions that can be subjected to collision-induced fragmentation to give structural information. A method has been developed that permits rapid coupling of taurine to unconjugated, glycine-conjugated, sulfated, and glucuronidated bile acids. The reaction is performed for 2 h at room temperature in aqueous pyridine hydrochloride buffer, with or without dioxane, using 0.1 M 1-ethyl-3-(3- dimethylaminopropyl) carbodiimide as the coupling agent and 0.2 M taurine. The yields are higher than 95%. In contrast to published coupling reactions, the method permits conjugation of bile acids with the labile 7α-hydroxy-3- oxo-4-ene structure.