Enantioselective Synthesis ofβ-Blockersvia Hydrolytic Kinetic Resolution of Terminal Oxiranes by Using Bimetallic Chiral {{2,2′-[Cyclohexane-1,2-diylbis(nitrilomethylidyne)]bis[phenolato]}(2−)}cobalt ([Co(salen)])-Type Complexes

Chiral Cobalt-Salen Complexes: Ubiquitous Species in Asymmetric Catalysis

Since the discovery of their extraordinary reactivity in the hydrolytic kinetic resolution of terminal epoxides about twenty years ago, chiral cobalt-salen complexes have been shown to be essential for many other asymmetric catalytic reactions. This account summarizes the inspiring works dedicated to the discovery of their new reactivity and their mode of action, as well as the new processes towards the optimization of their cooperativity for bimetallic activation and the implementation of their effective immobilization, including also our contribution on these topics.

Chiral bisoxazoline ligands designed to stabilize bimetallic complexes

Chiral bisoxazoline ligands containing naphthyridine, pyridazine, pyrazole, and phenol bridging units were prepared and shown to form bimetallic complexes with various metal salts. X-ray crystal structures of bis-nickel naphthyridine-bridged, bis-zinc pyridazine-bridged, and bis-nickel as well as bis-palladium pyrazole-bridged complexes were obtained.

Fast liquid chromatography for racemic atenolol acetate separation-The analytical protocol

Kinetic resolution of (R,S)-atenolol is a faster strategy to produce (S)-atenolol. Since this racemate is a less soluble compound, resolution of its ester offers high concentrations in the process. A good analytical method is required to observe the enantiomer concentrations. This paper described application of ultra-fast liquid chromatography on the atenolol ester separation using different resolution media and analytical procedures. Chiralcel OD column resolved the ester. The chromatograms indicated different characteristics of the process. The enantiomers could be recognized by the column in less than 1 (one) hour. Symmetrical peaks were obtained, but several procedures produced peaks with wide bases and slanted baselines. Efficient enantioresolution was obtained at high mobile phase flow rate, decreased concentration of amine-type modifier, but increased alcohol content in the mobile phase. High UV detection wavelength was required. At 1.0 mL/min, the (90/10/0.5) composition resulted α = 1.46 and R_S  = 0.9998 that were good separation.

Enantio-conversion and -selectivity of racemic atenolol kinetic resolution using free Pseudomonas fluorescens lipase (Amano) conducted via transesterification reaction

Effects of reaction parameters on kinetic resolution of racemic atenolol usingPseudomonas fluorescenslipase were investigatedviatransesterification for production of pharmacologically active eutomer (S)-atenolol with high enantiomeric purity.

Lipase-catalyzed green synthesis of enantiopure atenolol

A new green route is proposed for the synthesis of enantiopure atenolol (a β₁-blocker).

Directed evolution of an enantioselective epoxide hydrolase: uncovering the source of enantioselectivity at each evolutionary stage

Directed evolution of enzymes as enantioselective catalysts in organic chemistry is an alternative to traditional asymmetric catalysis using chiral transition-metal complexes or organocatalysts, the different approaches often being complementary. Moreover, directed evolution studies allow us to learn more about how enzymes perform mechanistically. The present study concerns a previously evolved highly enantioselective mutant of the epoxide hydrolase from Aspergillus niger in the hydrolytic kinetic resolution of racemic glycidyl phenyl ether. Kinetic data, molecular dynamics calculations, molecular modeling, inhibition experiments, and X-ray structural work for the wild-type (WT) enzyme and the best mutant reveal the basis of the large increase in enantioselectivity (E = 4.6 versus E = 115). The overall structures of the WT and the mutant are essentially identical, but dramatic differences are observed in the active site as revealed by the X-ray structures. All of the experimental and computational results support a model in which productive positioning of the preferred (S)-glycidyl phenyl ether, but not the (R)-enantiomer, forms the basis of enhanced enantioselectivity. Predictions regarding substrate scope and enantioselectivity of the best mutant are shown to be possible.