Regio- and stereoselective reductions of dehydrocholic acid.

Dehydrocholic acid (DHCA), an unnatural bile acid, is manufactured by oxidation of cholic acid. Its biotransformation by two basidiomycetes (Trametes hirsuta and Collybia velutipes) is reported. These mycelia showed different affinities for the substrate and selectivities of attack: T. hirsuta in particular regio- and stereoselectively reduced the 3-keto group to yield 3 alpha-hydroxy-7,12-diketo-5 beta-cholan-24-oic acid (7,12-diketolithocolic acid) as the main product. A number of different chemical reductions were carried out on DHCA; among them hydrogenation with Raney Nickel in water under high-intensity ultrasound proved highly regio- and stereoselective, yielding 7,12-diketolithocolic acid exclusively. (1)H and (13)C resonances were assigned in details thanks to a series of 1D and 2D NMR runs including DEPT, NOESY, H-H COSY, gHSQC and gHMBC.