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The biocatalytic oxidation of racemic O - S -dimethyl O - p -nitrophenyl phosphorodithioate 5 catalyzed by chloroperoxidase from Caldariomyces fumago resulted in the formation of the (−)-( S )-enantiomer of the corresponding oxon 4 and unoxidized substrate 5 with a (+)-( R )-configuration. Both compounds were obtained with very high enantiomeric excesses, 99.6% and 97%, respectively. The thionation reaction of the resulting (−)-( S )-oxon 4 with Lawesson’s reagent gave (−)-( S ) - phosphorodithioate 5 with full stereoselectivity, while the oxidation of unreacted substrate (+)-( R )- 5 with iodoxybenzene afforded oxon (+)-( R )- 4 with 94.9% ee.

Polyleucines of various lengths act as enantioselective catalysts in the aldol condensation between cyclohexanone and a series of aromatic aldehydes, a reaction which may be of prebiotic significance.

The ee values of lactone 3 , and not of lactone 2 , obtained from the enantiodivergent oxidation of racemic bicyclo[3.2.0]hept-2-en-6-one 1 , catalyzed by cyclohexanone monooxygenase from Acinetobacter calcoaceticus , were found to be markedly dependent on the degree of conversion and substrate concentration. The results are rationalized on the basis of a model which hypothesizes the binding of a second substrate molecule to an enzyme site distinct from the catalytic site.

The enantiomers of tertiary amine oxides 3 show NMR spectral nonequivalence in the presence of (−)-(S)- or (+)-(R)-t-butylphenylphosphinothioic acid 4. It is observed even for the e-methyl protons and is large enough to determine the ee values of 3 having long alkyl chains. The enantiomeric thioacids 4 induce also an extremely large magnetic nonequivalence of the geminal N-methylene protons in 3.

An extension to Baeyer-Villiger oxidations of the active site model previously developed (Tetrahedron: Asymmetry, 1995, 6, 1375) for the enantioselective sulfoxidation of organic sulfides catalyzed by cyclohexanone monooxygenase from Acinetobacter NCIMB 9871 is proposed. The model is based on cubic-space descriptors and can explain the stereoselectivity of the enzyme for about 40 different substrates.

An active site model to explain and predict the stereoselectivity of the sultoxidation of organic sulfides to optically active sulfoxides catalyzed by cyclohexanone monooxygenase from Acinetobacter NCIB 9871 is proposed. The model is based on cubic-space descriptors and derives from the results obtained with over 30 different sulfides. The model, which also appears to be suitable for explaining the stereoselectivity of cyclohexanone monooxygenase-catalyzed Baeyer-Villiger reactions, is consistent with and expands on the features of other previously described models for the latter process.

Chloroperoxidase catalysed epoxidadon of styrene derivatives by t -BuOOH preferentially gives (R) oxides with ee values between 28 and 68%. The data support the view of oxygen delivery from the ferryl oxygen directly to the substrate.

A systematic study of the stereochemistry of oxidation at sulfur catalyzed by cyclohexanone monooxygenase from Acinetobacter using as the substrates numerous alkyl aryl sulfides, dialkyl sulfides and dialkyl disulfides has been earned out. It was found that the structure of the sulfide dramatically influenced the enantioselectivity of the enzyme which yielded sulfoxides with optical purities ranging from 99% ee and R-configuration to 93% ee and S-configuration.

An optically pure (+)-S-Halostachine analogue 5a was synthesized in 57% total yield and in three steps from optically pure (−)-aR-[o-tolualdehyde]-chromium-tricarbonyl complex 2b . Various optically pure Halostachine analogues having an ortho-substituted aromatic ring and of both configurations (R and S) are thus available by this route. An X-ray structure of the intermediate complexed oxazoline 3bI allowed to confirm the model we proposed for the approach of a nucleophile on these arene complexes.

High enantioselectivities were obtained in chloroperoxidase catalyzed oxidation of organic sulfides ( 99% ee in the case of methyl 2-pyridyl sulfide) with H 2 O 2 in aqueous buffer solution, pH 5, at 25°C. The kinetic parameters in the oxidation of a series of sulfides both with H 2 O 2 and tert -butyl hydroperoxide were determined and the data are consistent with enzymatic oxidation involving presumably a ternary complex, in all cases the reaction afforded the (R) sulfoxide as predominant or exclusive enantiomer.