1H and 13C NMR characterization and stereochemical assignments of bile acids in aqueous media

The unconjugated bile acids cholic acid, deoxycholic acid, and chenodeoxycholic acid; their glycine and taurine conjugates glycocholic acid, glycocleoxycholic acid, glycochenodeoxycholic acid, taurocholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid; and a taurine conjugated ursodeoxycholic acid, tauroursocleoxycholic acid, were characterized through H-1 and C-13 NMR in aqueous media under the physiological pH region (7.4 +/- 0.1). Assignments of 1 H and 13C signals of all the bile acids were made using a combination of several one- and two-dimensional, homonuclear (H-1-H-1) and heteronuclear (H-1-C-13) correlations as well as spectral editing NMR methods. Stereochemical assignment of the five-membered ring of the bile acids is reported here for the first time. The complete characterization of various bile acids in aqueous media presented here may have implications in the study of the pathophysiology of biliary diseases through human biliary fluids using NMR spectroscopy.