The enzyme 6-oxocamphor hydrolase (OCH) from Rhodococcus sp. NCIMB 9784 catalyses the cleavage of a carbon-carbon bond between two carbonyl groups in both mono-and bicyclic non-enolisable b-diketone substrates. In this mode OCH has been shown to effect the desymmetrisation of both bridged symmetrical bicyclic [2.2.1] and [2.2.2] systems and a series of 1-alkylbicycloA C H T U N G T R E N N U N G [3.3.0]octane-2,8-diones, yielding chiral substituted cyclopentanone and cyclohexanone products in high optical purity. In the present study, OCH has been challenged with a series of heteroannular substrates including 1-methylbicycloA C H T U N G T R E N N U N G [4.3.0]nonane-2,9-dione (7a-methylhexahydroindene-1,7-dione) in an effort to assess the competence of the enzyme for kinetic resolutions of asymmetric, racemic substrates. OCH was shown to catalyse the resolution of 1-methylbicyclo-A C H T U N G T R E N N U N G [4.3.0]nonane-2,9-dione with an E value of 2.9. The effect of increasing the length of the alkyl chain in the 1-position, or enlarging one of the rings, was to increase the enantioselectivity of the enzyme to 5.7 and 3.1 for the substrates 1-allylbicyclo-(9a-methyloctahydrobenzocycloheptene-1,9-dione) was not a substrate for OCH. These experiments constitute the first description of the resolution behaviour of such a retro-Claisenase enzyme, and suggest a maximum steric limit for substrate recognition by OCH.
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