Cyclohexanone oxygenase, from Acinetobacter NCIB 9871, has been incubated with (2S,6S)-[2,6-2H2]-and (27?) -[ 2-2H, ]cyclohexanone. The resulting labeled c-caprolactone (2-oxepanone) samples were degraded to 1-pentanol, which was esterified by using (-)-camphanyl chloride. Analysis of the camphanates by deuterium NMR spectroscopy, using Eu(dpm)3, showed that the conversion of ketone to lactone had in each case proceeded with complete retention of configuration at the migrating carbon center. A similar degradation of (27?)-[2-2H1]cyclohexanone itself showed that reduction of [2-2H,]cyclohex-2-enone by Beauveria bassiana ATCC 7159 is also completely stereoselective. A method has been developed for assessing the enantioselectivity of enzymes toward racemic substrate mixtures. (2R)-2-[methyl-2H3]-and (2S)-2-[methyl-13C] methylcyclohexanone were synthesized and mixed in equal amounts, and the resulting mixture (a virtual racemate) was incubated with cyclohexanone oxygenase. The course of the reaction was followed by both 13C and 2H NMR spectroscopy, showing that the initial rate of oxidation of the 2S enantiomer was nearly twice that of the 2R enantiomer. (27?)-and (2S)-2-methylcyclohexanone were both converted by cyclohexanone oxygenase to 6-methyl-e-caprolactone (7-methyl-2-oxepanone).Advantages of the virtual racemate/multinuclear NMR technique over existing methodology are described.While the Baeyer-Villiger reaction3 has been a standard tool of organic chemistry for the better part of a century, only in recent years has it become clear that nature makes widespread use of this reaction in biodegradative pathways.4 Studies in several f Dedicated to Dr. Ulrich Weiss on the occasion of his 75th birthday.

Anhand von eingehenden Versuchen mit deuterierten Substraten wird gezeigt, daß die Überführung von Cyclohexanon (I) in e‐Caprolactam (II) mittels Cyclohexanonoxygenase (Cox.) (aus Acinetobacter NCIB 987l) unter vollständige; Konfigurationsretention am wandernden C‐Zentrum verläuft.