The oxidative oligomerization of a chiral mandelamide derivative (N-(4-hydroxyphenyl)mandelamide, 1) was performed in the presence of horseradish peroxidase, laccase and N,N'-bis(salicylidene)ethylenediamine-iron(II) to obtain chiral oligophenols 2. The low enantioselectivity of the enzymatic catalyzed asymmetric enantiomer-differentiating oligomerizations was investigated. In addition, the poo...

A series of BoPhoz-type ligands were successfully applied in the rhodium-catalyzed asymmetric hydrogenation of a number of beta-substituted or unsubstituted alpha-(phthalimidomethyl)acrylates, affording good to excellent enantioselectivities. The results suggested that the presence of an N-H proton in the BoPhoz backbone could significantly improve the enantioselectivity, and ligand (Sc,Rp)-1d,...

INTRODUCTION A number of studies on enzymatic reactions have been carried out in organic media. These reactions have several benefits compared with conventional organic synthesis, including high enantioselectivity, substrate specificity and low energy consumption. There are, however, several drawbacks in using organic solvents. Volatile organic solvents are often flammable and toxic to the envi...

Water concentration affects both the enantioselectivity and activity of enzymes in dry organic media. Its influence has been investigated using the hydrocyanation of benzaldehyde catalyzed by hydroxynitrile lyase cross-linked enzyme aggregate (MeHNL-CLEA) as a model reaction. The enzyme displayed higher enantioselectivity at higher water concentration, thus suggesting a positive effect of enzym...

A new chiral stationary phase (CSP) was prepared by attachment of macrocyclic glycopeptide antibiotic eremomycin to the epoxy-activated silica under mild conditions. In contrast to CSP with immobilized vancomycin, which is a close structural analogue of eremomycin, the prepared CSP reveals high enantioselectivity for separation of amino acids enantiomers. It was demonstrated by the example of r...

A systematic study of the effect of substitution within the beta-amino acid framework indicates that both beta(2)- and beta(3)-amino acids catalyse the Hajos-Parrish-Eder-Sauer-Wiechert reaction with poor to reasonable levels of enantioselectivity. These results led to the evaluation of the conformationally constrained beta-amino acid (1R,2S)-cispentacin, which catalyses the Hajos-Parrish-Eder-...

New chiral S,N- and S,P-ligands starting from tert-butanesulfinamide were synthesized in four steps, applying Pd-catalyzed asymmetric allylic substitutions of dimethyl 2-fluoromalonate. The induced effect of the Pd/S,N-ligand catalyst on the enantioselectivity depends on the steric demand of the substituent at the o-position of the pyridine ring. This method produced monofluorinated allylation ...

An asymmetric annulation reaction of γ-butenolides and cyclic 1-azadienes containing a 1,2-benzoisothiazole-1,1-dioxide motif has been studied, proceeding in a tandem Michael addition-aza-Michael addition sequence. Endo-type cycloadducts bearing fused tetracyclic skeletons were isolated in fair yields and with high enantioselectivity (up to >99% ee) under the catalysis of modified cinchona alka...

We emphasize the importance of dynamics and hydration for enzymatic catalysis and protein design by transplanting the active site from a haloalkane dehalogenase with high enantioselectivity to nonselective dehalogenase. Protein crystallography confirms that the active site geometry of the redesigned dehalogenase matches that of the target, but its enantioselectivity remains low. Time-dependent ...

Nonlinear effects in asymmetric synthesis and the occasionally observed reversal of the enantioselectivity of the employed catalyst are evaluated by a generalized kinetic approach. A non-autocatalytic and an autocatalytic reaction system are considered as two different prototype scenarios. It is predicted that during the course of enantioselectivity reversal in the non-autocatalytic system a gr...