Nicoletta Gaggero

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.

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.

Enantioselective oxidation of sulphides by dioxiranes in the presence of bovine serum albumin

Abstract Oxidation of sulphides by in situ generated dioxiranes in buffered (pH 7.5) aqueous solutions, using bovine serum albumin (BSA) as a chiral auxiliary, affords the corresponding sulphoxides in up to 89% enantiomeric excess (e.e.).

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.

Enantioselective oxidation of sulphides to sulphoxides in the presence of bovine serum albumin

Abstract In situ generated dioxiranes oxidize a series of prochiral sulphides to the corresponding sulphoxides with enantiomeric excess (e.e.) up to 89%, when bovine serum albumin (BSA) is used as chiral auxiliary. The degree of enantioselectivity, as well as yield and reaction times, depend upon the nature of the dioxirane. These are compared with enantioselectivities attainable for the same transformations by using peroxomonosulfate alone, i.e. in the absence of ketone. In the oxidation of prochiral keto sulphides (wherein the carbonyl functionality serves as precursor of dioxirane) with peroxomonosulfate, optically active keto sulphoxides are isolated in satisfactory chemical and optical yield (up to e.e. 84%).

Asymmetric weitz - scheffer epoxidation promoted by bovine serum albumin: Part III. Highly stereoselective synthesis of optically active epoxynaphthoquimones

Abstract The epoxidation of 2-substituted naphthoquinones with t-BuOOH in an aqueous buffer solution containing a small amount (up to 5 % molar equiv) of bovine serum albumin (BSA) gives the corresponding epoxides with enantiomeric excess (e.e.) up to 100 %. The enantioselectivity is very sensitive to the addition of water miscible or immiscible cosolvents and to the length of the alkyl chain in position 2. The mechanism by which the cosolvents influence the e.e. was studied. Correlations between the circular dichroism spectra of the BSA-quinone complexes and the stereochemistry of the epoxidation products were found.

Effect of substrate concentration on the enantioselectivity of cyclohexanone monooxygenase from Acinetobacter calcoaceticus and its rationalization

Abstract 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.

Albumin as a promiscuous biocatalyst in organic synthesis

Albumin emerged as a biocatalyst in 1980 and the continuing interest in this protein is proved by numerous papers. The use of albumin was initially confined to the field of asymmetric oxidations and reductions, but more recently it has found a broader application to chemical reactions such as additions, condensations and eliminations. This review reports the main applications of albumin in organic synthesis that have appeared in the literature in the past decade.