Piero Pasta

Chloroperoxidase and hydrogen peroxide: An efficient system for enzymatic enantioselective sulfoxidations.

Abstract 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.

Enantioselective epoxidation of styrene derivatives by chloroperoxidase catalysis

Abstract 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.

First asymmetric epoxidation catalysed by cyclohexanone monooxygenase

The first example of a totally enantioselective epoxidation mediated by cyclohexanone monooxygenase for a model compound related to fosfomycin is reported.

A predictive active site model for the cyclohexanone monooxygenase catalyzed oxidation of sulfides to chiral sulfoxides

Abstract 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.

Subtilisin-catalyzed transesterification in supercritical carbon dioxide

SummarySubtilisin Carlsberg was found to catalyze transesterification between N-acetyl-L-phenylalanine chloroethyl ester and ethanol in supercritical carbon dioxide. The effects of different temperatures and carbon dioxide/ethanol ratios on the reaction rate were investigated. A comparative study showed that enzymatic transesterification is faster in supercritical carbon dioxide than in anhydrous organic solvents.

Microbiological transformations 36: Preparative scale synthesis of chiral thioacetal and thioketal sulfoxides using whole-cell biotransformations

Abstract This work describes the preparative scale enantioselective oxidation of some prochiral dithioacetals and dithioketals to their corresponding chiral monosulfoxides using whole-cell cultures of microorganisms.

Enzymatic oxidoreduction of steroids in two-phase systems: Effects of organic solvents on enzyme kinetics and evaluation of the performance of different reactors

Abstract The preparative-scale regio- and stereospecific oxidoreduction of the hydroxyl-keto groups of a variety of steroids, catalysed by several hydroxysteroid dehydrogenases, has been carried out in water—organic solvent two-phase systems. The organic solvents employed were ethyl and butyl acetate. The steroid transformations were specific, complete, and one-step. In the systems containing ethyl acetate, the transformation rates were different from those obtained in butyl acetate because of the different effects of the two solvents on such parameters as K m , V max , product inhibition constant, and the partition coefficient of steroids. Various reactors (free enzymes in shaken vessels, immobilized enzymes in shaken vessels, and fixed bed reactors) have been made and their performance compared. The suitability to two-phase systems of several enzymatic NAD(P)(H)-regenerating systems has also been studied.

THE MICROPEROXIDASE-11 CATALYZED OXIDATION OF SULFIDES IS ENANTIOSELECTIVE

Abstract Microperoxidase-11 catalyzed oxidation of alkyl aryl sulfides by H2O2 preferentially give the (−)-(S)-sulfoxides (e.e. 16 – 25 %).

Chloroperoxidase-catalyzed enantioselective oxidation of methyl phenyl sulfide with dihydroxyfumaric acid/oxygen or ascorbic acid/oxygen as oxidants

The chloroperoxidase catalyzed oxidation of methyl phenyl sulfide to (R)-methyl phenyl sulfoxide was investigated, both in batch and membrane reactors, using as oxidant H2O2, or O2 in the presence of either dihydroxyfumaric acid or ascorbic acid. The effects of pH and nature and concentration of the oxidants on the selectivity, stability, and productivity of the enzyme were evaluated. The highest selectivity was displayed by ascorbic acid/O2, even though the activity of chloroperoxidase with this system was lower than that obtained with the others. When the reaction was carried out in a membrane reactor, it was possible to reuse the enzyme for several conversion cycles. The results obtained with ascorbic acid/O2 and dihydroxyfumaric acid/O2 as oxidants do not seem to be compatible with either a mechanism involving hydroxyl radicals as the active species or with the hypothesis that oxidation occurs through the initial formation of H2O2. Copyright 1999 John Wiley & Sons, Inc.

Synthesis of chiral benzyl alkyl sulfoxides by cyclohexanone monooxygenase from Acinetobacter NCIB 9871

Abstract Benzyl alkyl sulfides with alkyl groups from methyl to hexyl, para -alkylbenzyl groups from methyl to butyl, 2-phenylethyl methyl sulfide and 3-phenylpropyl methyl sulfide have been oxidized by cyclohexanone monooxygenase from Acinetobacter NCIB 9871. Sulfoxides with enantiomeric excesses ranging from 80% for the ( R )-configuration to 96% ee for the ( S )-configuration were obtained.