Vulpecholic acid (1α,3α,7α-trihydroxy-5β-cholan-24-oic acid): A novel bile acid of a marsupial, Trichosurus vulpecula (Lesson)

Abstract

A novel trihydroxylated C 24 bile acid was isolated from the gallbladder bile of the Australian opossum, Trichosurus vulpecula (Lesson). This acid, for which the name vulpecholic acid is proposed, was identified as 1α,3α,7α-trihydroxy-5β-cholan-24-oic. The structure proof included mass spectral and 1H and 13C nuclear magnetic resonance characterization of all crucial derivatives obtained by: a) oxidation of the methyl ester to a triketone with the enolizable 1,3-diketone function; b) methylation of this triketone to two isomeric methyl enol ethers; and c) reductive removal of oxygen functions from this triketone to give 5β-cholan-24-oic and 7-oxo-5β-cholan-24-oic acids. Vulpecholic acid was found in the bile in the unconjugated form; it accounted for more than 60% of the solid bile material. The marsupial T. vulpecula is the first example of a mammal secreting a 1α-hydroxylated bile acid as well as the first example of a mammal secreting the major bile acid in a free form.