Search

1,cis-2-Dihydroxycyclohexa-3,5-diene-1-carboxylic acid, 2, produced by Pseudomonas putide, U103, was shown via X-ray analysis of its p-bromobenzoylmethyl ester to have (1S 2R) absolute stereochemistry. The stereo- and regio-selectivity of a series of cycloadditions of the methyl ester 3(R = Me) the methyl ester acetonide 5 and the hydroxymethylacetonide 6(R = H) with singlet oxygen, 4-phenyl-4,5-dihydro-3H-1,2,4-triazole-3,5-dione, N-phenylmaleimide and nitrosobenzene have been established. The stereochemistry of the oxygen adduct 7 of 5 was unambiguously assigned by X-ray analysis of 7. The acetonides 5 and 6(R = H) were attacked by the dienophiles anti to the acetonide group. The diol ester 3 underwent attack on the face syn to the diol groups. The regiochemistry of the addition of nitrosobenzene was predominantly with the N–phenyl group distal to the ester function in 3 and 5, but proximal to the hydroxymethyl group in 6(R = H).

The absolute stereochemistry of the 2-carboxy-cis-1,2-dihydro-1,2-dihydroxynaphthalene, a diol produced by Pseudomonas testosteroni A3C, was shown by X-ray crystal analysis to be 1R,2S

The synthesis of several 2,4-diketo carboxylic acids by standard methods was undertaken to study the substrate specificity of the carbon-carbon bond hydrolases. It was shown by 1H- and 13C-NMR experiments that compounds with 4-alkyl, 4-alkenyl and 4-alicyclic substituents exist in three main forms: 2,4-diketo, 2-enol-4-keto and 2-hydrate-4-keto. The equilibrium ratios of these aqueous solution structures were similar, but were markedly affected by the pH values (1.5–10.5). At pH 7.5 the ratio of these structures was approximately 4:5:1, but at low pH values the 2-hydrate predominated (≈50%) and at high pH values the 2-enolate carboxylate was dominant (≈80%) while the 2-hydrate was not detected. 4-Aryl substituents gave one pH-independent isomer formulated with C-2, C-3 and C-4 electrons delocalized in conjugation with the arene at C-4. This interpretation of a very rapid equilibrium between 2- and 4-enolate isomers to give a π-delocalized six-membered ring in conjugation with arene substituents is supported by the effect of divalent metal ions on the structural forms. Rate and equilibrium constants for several of these solution interconversions are influenced by pH. Mg2+ coordinates to the 2-enolate dianion of alkyl analogues, whereas Cu2+ forms a six-membered π-delocalized ring with the 2- and 4-oxo atoms in conjugation with the arenes. Exchange of 2H from 2H2O-enriched solvent occurs with the protons at C-3. The dimers of the 4-alkyl analogues inaqua were characterized as a product of self-aldol condensations. These data have facilitated enzyme mechanism studies of C–C bond hydrolysases (β-ketolases).

Fluorochemicals are rare in Nature and fluoroaromatic compounds have not been described as natural products with respect to de novo formation of aryl-fluorine bonds. By contrast many synthetic fluoroaromatic compounds are substrates for several microbial enzymes, particularly oxygenases, and are transformed to previously undescribed fluorochemicals suitable for further modifications by other enzymes systems or by chemical means. These lead to interesting multi-functional molecules, monomers for novel chiral and achiral polymers, chiral intermediates and synthons for some heterocycles and α- amino acids. Wild-type and mutant microbial strains have been used to biotransform some fluoroaromatic compounds in near quantitative yields to novel fluorinated products, as well as other flourophenolics already known by chemical synthesis. Some of the microbial transformations of mono-, di-, tri- and tetrafluoroaromatic compounds are described, and the vast potential of further biotransformations is indicated.