Identification of a novel bile acid in swans, tree ducks, and geese: 3α,7α,15α-trihydroxy-5β-cholan-24-oic acid

By HPLC, a taurine-conjugated bile acid with a retention time different from that of taurocholate was found to be present in the bile of the black-necked swan, Cygnus melanocoryphus. The bile acid was isolated and its structure, established by 1H and 13C NMR and mass spectrometry, was that of the taurine N-acyl amidate of 3α,7α,15α-trihydroxy-5β-cholan-24-oic acid. The compound was shown to have chromatographic and spectroscopic properties that were identical to those of the taurine conjugate of authentic 3α,7α,15α-trihydroxy-5β-cholan-24-oic acid, previously synthesized by us from ursodeoxycholic acid. By HPLC, the taurine conjugate of 3α,7α,15α-trihydroxy-5β-cholan-24-oic acid was found to be present in 6 of 6 species in the subfamily Dendrocygninae (tree ducks) and in 10 of 13 species in the subfamily Anserinae (swans and geese) but not in other subfamilies in the Anatidae family. It was also not present in species from the other two families of the order Anseriformes. 3α,7α,15α-Trihydroxy-5β-cholan-24-oic acid is a new primary bile acid that is present in the biliary bile acids of swans, tree ducks, and geese and may be termed 15α-hydroxy-chenodeoxycholic acid.