Mixed oxo-hydroxy bile acids as actual or potential impurities in ursodeoxycholic acid preparation: a 1H and 13C NMR study.

Some distinctive unprecedented 1H NMR signals and the complete 13C NMR resonances are assigned for the entire set of mixed oxo-hydroxy bile acid isomers, obtained by selective oxidation of the hydroxy groups at positions (3,7), (3,12) and (3,7,12) of chenodesoxycholic acid, desoxycholic acid and cholic acid, respectively. Partially or totally oxidized products are the major actual or potential impurities formed during the preparation of the pharmaceutically active ursodeoxycholic and chenodeoxycholic acids.