Biocatalytic production of mandelic acid and analogues: a review and comparison with chemical processes.

The aim of this study is to summarize the current progress in the design of biocatalytic processes applicable for the production of optically pure mandelic acids and their analogues. These compounds are used as building blocks for pharmaceutical chemistry and as chiral resolving agents. Their enzymatic syntheses mainly employed nitrile hydrolysis with nitrilases, ester hydrolysis, ammonolysis or esterification with lipases or esterases, and ketone reduction or alcohol oxidation with dehydrogenases. Each of these methods will be characterized in terms of its product concentrations, enantioselectivities, and the types of catalysts used. This review will focus on the dynamic kinetic resolution of mandelonitrile and analogues by nitrilases resulting in the production of high concentrations of (R)-mandelic acid or (R)-2-chloromandelic acid with excellent e.e. Currently, there is no comparable process for (S)-mandelic acids. However, the coupling of the S-selective cyanation of benzaldehyde with the enantioretentive hydrolysis of (S)-mandelonitrile thus obtained is a promising strategy. The major product can be changed from (S)-acid to (S)-amide using nitrilase mutants. The competitiveness of the biocatalytic and chemical processes will be assessed. This review covers the literature published within 2003-2017.