Asymmetric transformations catalyzed by enzymes in organic solvents

Tetrahedron report number 203

The high cost of nicotinamide cofactors requires that they be regeneratedin situ when used in preparative enzymatic synthesis. Numerous strategies have been tested forin situ regeneration of reduced and oxidized cofactors. Regeneration of reduced cofactors is relatively straightforward; regeneration of oxidized cofactors is more difficult. This review summarizes methods for preparation of the cofactors, factors influencing their stability and lifetime in solution, methods for theirin situ regeneration, and process considerations relevant to their use in synthesis.

Regeneration of nicotinamide cofactors for use in organic synthesis.

http://www.enisonlabs.com/Chemiluminescence%20as%20diagnostic%20tool.%20A%20review.pdf

Chemiluminescence as diagnostic tool. A review

Multi-enzymatic cascade reactions, i.e., the combination of several enzymatic transformations in concurrent one-pot processes, offer considerable advantages: the demand of time, costs and chemicals for product recovery may be reduced, reversible reactions can be driven to completion and the concentration of harmful or unstable compounds can be kept to a minimum. This review summarizes the developments in multi-enzymatic cascades employed for the asymmetric synthesis of chiral alcohols, amines and amino acids, as well as for CC bond formation. In addition, a general classification of biocatalytic cascade systems is provided and bioprocess engineering aspects associated with the topic are discussed.

Multi-Enzymatic Cascade Reactions: Overview and Perspectives

Resolution of the mucolytic drug (±)- trans -sobrerol ( 1 ) was achieved by transesterification with vinyl acetate in organic media, catalyzed by free or immobilized Lipase PS. The enantioselectivity of the enzyme was markedly influenced by the nature of the organic solvent, but there was no correlation between enantiomeric ratio values (70–500) and either the hydrophobicity or the dielectric constant of the medium. With the enzyme immobilized onto Hyflo Super Cell and t -amyl alcohol as the solvent, the selectivity of Lipase PS for (−)- 1 was extremely high and, at 50 % conversion both (−)- trans -sobrerol and (+)- trans -sobrerol monoacetate were obtained in practically 100 % optical purity

Resolution of (±)-trans-sobrerol by lipase PS-catalyzed transesterification and effects of organic solvents on enantioselectivity

The Vmax and KM of various forms of lipase from Pseudomonas cepacia (powder, adsorbed onto Celite or covalently linked to polyethylene glycol) were determined in organic solvents preequilibrated to water activities (aw) from <0.1 to 0.84. The model reaction was the transesterification between n-octanol and vinyl butyrate. It was found that KM for the nucleophile increased with increasing aw for all three lipase forms. Vmax increased with increasing aw for polyethylene glycol-lipase, whereas there was an optimum at intermediate aw values (0.11 – 0.38) for lipase powder and Celite-immobilized lipase.

Effects of water activity on Vmax and KM of lipase catalyzed transesterification in organic media

Preparative-scale regio- and stereospecific oxidoreduction of cholic acid and dehydrocholic acid catalyzed by hydroxysteroid dehydrogenases

Chemiluminescent flow sensor for the determination of Paraoxon and Aldicarb pesticides

The activity and enantioselectivity of Lipase PS from Pseudomonas cepacia and lipoprotein lipase from Pseudomonas sp. were investigated in organic solvents preequilibrated to water activities ranging from <0.1 to 0.53, using as a model reaction the transesterification between (±)-sulcatol and vinyl acetate. Variations of water activity markedly influenced the transesterification rate but did not modify the enantioselectivity of the two enzymes.

Roberto Bovara

Papers

Resolution of (±)-trans-sobrerol by lipase PS-catalyzed transesterification and effects of organic solvents on enantioselectivity

Effects of water activity on Vmax and KM of lipase catalyzed transesterification in organic media

Preparative-scale regio- and stereospecific oxidoreduction of cholic acid and dehydrocholic acid catalyzed by hydroxysteroid dehydrogenases

Chemiluminescent flow sensor for the determination of Paraoxon and Aldicarb pesticides

Water activity does not influence the enantioselectivity of Lipase PS and lipoprotein lipase in organic solvents