Bacterial metabolism of 6,7-dihydro-5H-benzocycloheptene by Pseudomonas putida. Synthesis and absolute configuration of benzylic alcohol and cis-diol metabolites of 6,7-dihydro-5H-benzocycloheptene

Abstract

Metabolism of 6,7-dihydro-5H-benzocycloheptene (1) by growing cultures of a mutant strain of Pseudomonas putida yielded benzylic monohydroxylation (6,7-dihydro-5-hydroxy-5H-benzocycloheptene)(2) and dihydroxylation (cis-6,7,8,9-tetrahydro-5,6-dihydroxy-5H-benzocycloheptene)(3) products. The monoalcohol (2) and diol (3) metabolites were found to be optically pure (98% enantiomeric excess) by chiral stationary phase HPLC analysis and ¹H NMR analysis of the 2-methoxy-2-phenyl-2-trifluoromethylacetyl (MTPA) derivatives. The absolute configurations of the (+)-(5R) alcohol (2) and (+)-(5S,6R)-diol (3) metabolites were assigned by stereochemical correlation methods to the (+)-(5S,6S)-trans-6-bromo-6,7,8,9-tetrahydro-5-hydroxy-5H-benzocycloheptene derivative (6a). Racemic bromohydrin (5) was resolved via the MTPA ester diastereoisomers. The absolute configuration of (–)-(5R,6R)-trans-6-bromo-6,7,8,9-tetrahydro-5-(2-methoxy-2-phenyl-2-trifluoromethylacetoxy)-5H-benzocycloheptene (6b) was unequivocally determined by X-ray crystallographic analysis. Optically pure samples of the microbial metabolites (2), (3), and (4) have been chemically synthesised from the (+)-(5S,6S)-trans-bromohydrin (5) and stereochemically assigned.