Asymmetric reduction of aryl trifluoromethyl ketones with an achiral NADH model compound in a chiral hydrophobic binding site of sodiumcholate micelle, β-cyclodextrin and bovine serum albumin

The fusion of homogeneous and enzymatic catalysis has recently drawn attention due to reported novel activities and high selectivities. The incorporation of metal-catalysts into proteins combines the advantages of both catalytic strategies. Herein we summarize recent approaches of artificial metalloenzymes applied to catalysis. The discussion includes different strategies of anchoring and screening for improved selectivity.

Use of common proteins with no distinctive redox functionalities as chiral templates for asymmetric oxidations and reductions represents an intriguing, but barely explored, phenomenon in biocatalysis. This review focuses on synthetically important and challenging reactions stereoselectively catalyzed or mediated by ubiquitous nonredox proteins, such as bovine serum albumin and chymotrypsin.

This chapter reviews that dihydropyridines and tetrahydropyridines represent the key intermediates for the enantioselective synthesis of indoloquinolizidine, benzoquinolizidine, indolizidine, and quinolizidine frameworks that in turn, might be transformed into various natural products. An electron-withdrawing group either on a nitrogen atom or on a ring stabilizes a dihydropyridine ring toward oxidation and polymerization. An electron-withdrawing substituent at a β-position enhances the electronegativity of the pyridine ring for nucleophilic addition, and stabilizes one of the double bonds of the dienamine toward acid or radical cyclization— that is, an unsubstituted enamine function cyclizes in a regiospecific manner onto the C2 position of the indole nucleus. Moreover, the presence of an electron-withdrawing group at the β-position of a dihydropyridine or tetrahydropyridine is often a requirement for their synthetic exploitation. The chapter highlights the applications of the methodology based on the “nonbiomimetic” oxidation of dihydropyridines for the diastereoselective synthesis of functionalized heterocyclic systems as potential precursors for bioactive or natural products. With the aim of developing alternative procedures for the synthesis of natural products, the preceding results significantly expand the scope, and the potential of the use of dihydropyridines and tetrahydropyridines as starting materials or intermediates.

Some recent developments in the use of main chain chiral polymer catalysts are summarized. These polymers are different from the traditional polymer catalysts that are prepared by anchoring monomeric chiral catalysts to an achiral polymer backbone. Three classes of synthetic main chain chiral polymers are discussed including: (1) helical polymers represented by polypeptides; (2) polymers with flexible chiral chains such as polyesters and polyamides; and (3) polymers of rigid and sterically regular chiral chains represented by chiral conjugated polybinaphthyls. Some of these polymer catalysts have shown high enantioselectivity in asymmetric organic transformations.

A general synthesis of C-4-substituted dihydropyridines is described. The route exploits a standard Hantzsch ester synthesis followed by nucleophilic substitution of a halide with, for example, triethylphosphite. The resulting compounds could have interesting biological properties or may find use as haptens for preparing catalytic antibodies for hydride transfer reactions.