Microbiological degradation of bile acids. The preparation of some hypothetical metabolites involved in cholic acid degradation

1. To identify the intermediates involved in the degradation of cholic acid, the further degradation of (4R)-4-[4a-(2-carboxyethyl)-3aa-hexahydro-7ab-methyl-5-oxoindan-1β-yl]valeric acid (IVa) by Arthrobacter simplex was attempted. The organism could not utilize this acid but some hypothetical intermediate metabolities of compound (IVa) were prepared for later use as reference compounds. 2. The nor homologue (IIIa) and the dinor homologue (IIIb) of compound (IVa) were prepared by exposure of 3-oxo-24-nor-5β-cholan-23-oic acid (I) and (20S)-3b-hydroxy-5-pregnene-20-carboxylic acid (II) to A. simplex respectively. These compounds correspond to the respective metabolites produced by the shortening of the valeric acid side chain of compound (IVa) in a manner analogous to the conventional fatty acid a- and b-oxidation mechanisms. Their structures were confirmed by partial synthesis. 3. The following authentic samples of reduction products of the oxodicarboxylic acids (IIIa), (IIIb) and (IVa) were also synthesized as hypothetical metabolities: (4R)-4-[3aa-hexahydro-5a-hydroxy-4a-(3-hydroxypropyl)-7ab-methylindan-1b-yl]valeric acid (Vb) and its nor homologue (VIIa) and dinor homologue (IXa);(4R)-4-[3Aaa-hexahydro-5a-hydroxy-4a-(3-hydroxypropyl)-7ab-methylindan-1b-yl]-pentan-1-ol (Vc); and their respective 5β epimers (Ve), (VIIc), (IXc) and (Vf). 4. In connexion with the non-utilization of compound (IVa) by A. simplex, the possibility that not all the metabolites formed from cholic acid by a certain micro-organism can be utilized by the same organism is considered.