STEREOSPECIFIC DEHYDROGENATION OF HA,7-ALPHA,12-ALPHA-TRIHYDROXY-5-BETA-CHOLESTANOIC AND HA,7-ALPHA,12-ALPHA-TRIHYDROXY-5-BETA-CHOLESTANOICACIDS BY ACYL-COA OXIDASE IN RAT-LIVER LIGHT MITOCHONDRIAL-FRACTION

From a stereochemical point of view, the dehydrogenation mechanism of the biotransformation of 3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-ch olestanoic acid (THCA) into (24E)-3 alpha,7 alpha,12 alpha-trihydroxy- 5 beta-cholest-24-enoic acid (Delta(24)-THCA) has been studied with ca pillary gas chromatography (GC)/negative ion chemical ionization (NICI )-mass spectrometry. After incubation of (24R,25R)- or (24S,25S)-[24,2 5-H-2(2)]THCA, synthesized from (24E)-Delta(24)-THCA by a deuterated d iimide reduction, with a rat liver light mitochondrial fraction, 5 bet a-cholestanoic acids were extracted and derivatized into a pentafluoro benzyl (PPB) ester-dimethylethylsilyl (DMES) ether. Subsequent resolut ion into THCA and Delta(24)-THCA was attained by GC on a cross-linked 5% phenylmethyl silicone fused-silica capillary column monitored with a corresponding characteristic carboxylate anion [M - PFB](-) in the N ICI mode. The stereospecific elimination of a pro-R hydrogen at C-24 i n both (25R)- and (25S)-THCA indicated syn-elimination for the former, whereas anti-elimination for the latter was observed.