New 9,10-secosteroids from biotransformations of bile acids with Rhodococcus ruber

The biotransformations of cholic, deoxycholic and hyocholic acids with Rhodococcus ruber are reported. In all biotransformations the C17-side chain is partially degraded and the new 9,10-secosteroids 4a (54%) and 4b (55%), are obtained from cholic and deoxycholic acids respectively. The loss of water from C(11)-C(12) of secosteroids 4a and 4b affords the compounds 5a (5%) and 5b (20%), respectively. On the other hand, in the biotransformation of hyocholic acid with R. ruber the 9,10-secosteroid 4c is not detected but, rearranging in an intramolecular hemiacetal form, it evolves to the final furan derivative 6c (35%) by easy elimination of two molecules of water. The new secosteroids were characterized through MS, IR, NMR and 2D NMR spectroscopy.