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Whereas the biochemical properties of the monooxygenase components that catalyze the oxidation of 2,5-diketocamphane and 3,6-diketocamphane (2,5-DKCMO and 3,6-DKCMO, respectively) in the initial catabolic steps of (؉) and (؊) isomeric forms of camphor (CAM) metabolism in Pseudomonas putida ATCC 17453 are relatively well characterized, the actual identity of the flavin reductase (Fred) component that provides the reduced flavin to the oxygenases has hitherto been ill defined. In this study, a 37-kDa Fred was purified from a camphor-induced culture of P. putida ATCC 17453

ABSTRACTA dimeric Baeyer-Villiger monooxygenase (BVMO) catalyzing the lactonization of 2-oxo-Δ3-4,5,5-trimethylcyclopentenylacetyl-coenzyme A (CoA), a key intermediate in the metabolism of camphor byPseudomonas putidaATCC 17453, had been initially characterized in 1983 by Ougham and coworkers (H. J. Ougham, D. G. Taylor, and P. W. Trudgill, J. Bacteriol. 153:140–152, 1983). Here we cloned and overexpressed the 2-oxo-Δ3-4,5,5-trimethylcyclopentenylacetyl-CoA monooxygenase (OTEMO) inEscherichia coliand determined its three-dimensional structure with bound flavin adenine dinucleotide (FAD) at a 1.95-Å resolution as well as with bound FAD and NADP+at a 2.0-Å resolution. OTEMO represents the first homodimeric type 1 BVMO structure bound to FAD/NADP+. A comparison of several crystal forms of OTEMO bound to FAD and NADP+revealed a conformational plasticity of several loop regions, some of which have been implicated in contributing to the substrate specificity profile of structurally related BVMOs. Substrate specificity studies confirmed that the 2-oxo-Δ3-4,5,5-trimethylcyclopentenylacetic acid coenzyme A ester is preferred over the free acid. However, the catalytic efficiency (kcat/Km) favors 2-n-hexyl cyclopentanone (4.3 × 105M−1s−1) as a substrate, although its affinity (Km= 32 μM) was lower than that of the CoA-activated substrate (Km= 18 μM). In whole-cell biotransformation experiments, OTEMO showed a unique enantiocomplementarity to the action of the prototypical cyclohexanone monooxygenase (CHMO) and appeared to be particularly useful for the oxidation of 4-substituted cyclohexanones. Overall, this work extends our understanding of the molecular structure and mechanistic complexity of the type 1 family of BVMOs and expands the catalytic repertoire of one of its original members.

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A series of benzoate esters (methyl, ethyl, n-Pr, i-Pr, n-Bu, t-Bu, allyl, and propargyl) were subjected to enzymatic dihydroxylation by E. coli JM 109(pDTG 601) strain in a whole-cell fermentation. The cis-cyclohexadienediols were obtained in yields of approximately 1g/L except for n-propyl- and i-propyl benzoate which were found to be poor substrates. n-Butyl and t-butyl benzoates were not oxidized at all. The absolute stereochemistry for all metabolites was determined by comparison with a standard prepared from (1S-cis)-3-bromo-3,5-cyclohexadiene-1,2-diol, whose absolute configuration is well established. The free diols were found to be quite stable compared to other cis-dihydrodiols of this type, however, their acetonides underwent a dimerization via a regio- and stereoselective Diels-Alder cycloaddition. The diol derived from ethyl benzoate was subjected to a stereo- and regioselective inverse electron demand Diels-Alder cycloadditions with several dienophiles. The new adducts were completely characterized. The hetero-Diels-Alder reaction of this diol with an acyl nitroso dienophile yielded regio- and stereoselectively a bicyclic oxazine, which upon reduction provided a useful derivative of amino shikimate that can be exploited in an approach to oseltamivir (Tamiflu) and other amino cyclitols. The diol was also converted to carba-alpha-L-galactopyranose to demonstrate its potential utility as a source of pseudo sugars. Experimental and spectral data are provided for all new compounds.

Hydrocodone was converted to various Nacyl derivatives via a one-pot N-demethylation/Nacylation protocol catalyzed by palladium(II). The procedure has also been successfully applied to several N-methyltropane alkaloids. A plausible mechanism is suggested.

Reaction of the Burgess reagent with a series of aliphatic and aromatic thiols led to the corresponding symmetrical disulfides in high yields. No olefins were detected in the reactions of aliphatic thiols.