Nuclear Magnetic Resonance Spectroscopy. Carbon-13 Spectra of Cholic Acids and Hydrocarbons Included in Sodium Desoxycholate Solutions

Abstract

The ^(13)C resonances of cholic, desoxycholic, chenodesoxycholic, and lithocholic acids and some of their derivatives have been recorded and assigned to specific carbons. Comparison of the carbon chemical shifts for steroids with cis and trans A/B ring junctions show substantial similarities for the atoms in the C and D rings but large differences for some of the atoms in the A and B rings. The task of making the assignments was facilitated by comparisons of the T_1 relaxation times of the carbon nuclei and the use of lanthanide shift reagents to separate the carbon resonances sufficiently to simplify the interpretation of the off-resonance, partially proton-decoupled, spectra. Sodium desoxycholate in D_2O solution gives rather broad carbon resonances for all but the methyl and the quaternary carbons, as expected for substantial intermolecular association. These solutions take up p-xylene and 2-methylnaphthalene in about 2:1 molar, ratios. The ^(13)C spectra of the substances so included indicate that there is considerable restriction of the molecular motion of the 2-methylnaphthalene, but relatively little of p-xylene.