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

Abstract

The unconjugated bile acids cholic acid, deoxycholic acid, and chenodeoxycholic acid; their glycine and taurine conjugates glycocholic acid, glycodeoxycholic acid, glycochenodeoxycholic acid, taurocholic acid, taurodeoxycholic acid, and taurochenodeoxycholic acid; and a taurine conjugated ursodeoxycholic acid, tauroursodeoxycholic acid, were characterized through 1H and 13C NMR in aqueous media under the physiological pH region (7.4 +/- 0.1). Assignments of 1H and 13C signals of all the bile acids were made using a combination of several one- and two-dimensional, homonuclear (1H-1H) and heteronuclear (1H-13C) 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.

Chemical Synthesis of Uncommon Natural Bile Acids: The 9α-Hydroxy Derivatives of Chenodeoxycholic and Lithocholic Acids

“…The complete 1 H-and 13 C-NMR signal assignments for compounds 9a and b, which were confirmed by comparison of bile acid analogs reported previously, [23][24][25] were compiled in Table 1 C-NMR signals were appeared at δ 71.6 (9a) and 71.8 (9b) for the methine C-3, at δ 77.0 (9a) and 79.5 (9b) for the quaternary C-9, and at δ 62.2 (9a, b) for the methylene C-24 in the distortionless enhancement by polarization transfer (DEPT) spectra. These observations provide strong evidence for the presence of an axially-oriented 9α-hydroxyl group in the cis 5β-steroid nucleus (see below).…”

“…The great variety of natural C 24 and C 27 bile acids, as well as C 27 bile alcohols, (together called bile salts) occurring in vertebrates can be explained by the evolution of differing biochemical pathways that serve to convert cholesterol into these multifunctional amphipathic compounds. Bile salt composition shows significant variation between orders but not between families, genera, or species, suggesting a biochemical trait providing clues to evolutionary relationships that complement anatomical and genetic analyses.…”

Structural Requirements for Cooperativity in Ileal Bile Acid-binding Proteins

“…The major difficulty in the structure determination of the complex consists in the assignment of the two identically bound molecules of bile acids. The chemical shift dispersion of GCDA protons is very poor, but the presence of the three methyl groups, C18, C19, and C21 (see Scheme 1 for numbering), which appear in the unbound bile salt as two high intensity singlets (reported chemical shifts for C18 and C19 are 0.67 and 0.93 ppm, respectively) and as a doublet (C21, 0.95ppm) resonating at high fields (45), constituted a good entry point for the assignment of the bound molecules. Twodimensional F 1 /F 2 -15 N, 13 C-filtered NOESY experiments performed on a [ 15 N, 13 C]cI-BABP⅐u-GCDA sample with L/P ϭ 4 were used to filter out 1 H protein signals, allowing the observation of the GCDA resonances.…”

Bile acids from a Marine Sponge-Associated Fungus Penicillium sp.

“…. These data suggested a structural similarity of 1 to the glycocholic acid 3 . The structure of compounds 2, 4 and 5 exhibited features similar to those of 1 ( Figure 1) and signals of methyl groups, hydroxyl groups and carbonyl carbons were found in NMR data.…”