Asymmetric reduction with chitosan/dihydronicotinamide conjugates: Influence of L-alanine spacer arms on reducing performance

Dihydronicotinamide groups have been immobilized on chitosan through L-alanine spacer arms to elucidate the influence of spacer arms on asymmetric reduction and thereby construct suitable molecular environment. The amino groups of chitosan were acylated with N-nicotinoyl-L-alanine, and the derivative was transformed into the corresponding dihydronicotinamide conjugate by subsequent quaternization of the nicotinoyl groups followed by reduction. The resulting conjugate was evaluated in the reduction of ethyl benzoylformate, and the introduction of L-alanine spacer arms proved to be effective to achieve considerable reducing performance in both the asymmetric selectivity and chemical yield. Furthermore, the conjugate was confirmed to be used repeatedly without appreciable lowering of the performance.