This study explores the covalent immobilization of three lipases (Lipase AK, from Pseudomonas fluorescens; Lipase PS, from Burkholderia cepacia; and CrL, from Candida rugosa) on four supports prepared by functionalization of mesoporous hollow silica microspheres (M540) with various bisepoxides as activating agents for production of novel lipase biocatalysts for enantiomer selective biotransformations of secondary alcohols. The influence of length, rigidity and hydrophobicity of the bisepoxide activating agents was investigated on the efficiency of immobilization and catalytic properties of the resulted twelve lipase biocatalysts. The hollow silica particles modified with the most beneficial bisepoxide activating agents resulted in novel biocatalysts capable for kinetic resolution of racemic 1-phenylethanol rac-1a and racemic octan-2-ol rac-1b with high activity and enantioselectivity.

The stereoselective synthesis of chiral heterocyclic carbene precursors and the structural features of their silver and gold complexes were investigated. The prepared compounds are all based on the imidazolidine scaffold and bear the bulky tert-butyl substituent on the backbone in a stereocontrolled manner. The majority of the synthesized carbene precursors carry an additional element of central chirality in the side chain, and for some of them on formation of their silver or gold complexes a third element of asymmetry, axial chirality through hindered rotation of the aromatic substituent, is also present. The systematic study of the stereoselective formation of the NHC precursors led to scalable routes without the need for chiral chromatography. The NHC precursors were transformed efficiently into their silver and gold complexes, whose structural features were studied in detail both in solution and in the solid phase.

The formal [2+2] cycloaddition of ketenes and imines, also known as Staudinger synthesis, is a facile method for the synthesis of biologically important β-lactam derivatives. In this paper two previously reported stereoselective reactions were investigated with computational methods. Our computations support experimental data that a chiral imine, derived from d-glyceraldehyde reacting with ketenes, yields almost exclusively one out of the possible four diastereomers. The reaction proceeds stepwise, first addition of the imine to the ketene yields an intermediate, then the product is formed in a conrotatory electrocyclization. Results indicate that the electrostatic repulsion of the chiral auxiliary group is the main factor of the stereoselectivity, but solvent and substituent effects are not negligible. Calculations were performed at M06-2X/6-31+G** level of theory combined with IEF-PCM solvation, in common solvents such as toluene, THF, dichloromethane, acetonitrile and water. These results provide useful insight for the development of new chiral auxiliaries and optimizing reaction parameters.

The Chan-Lam-Evans