Biotransformations

This report reviews significant developments in the application of biological catalysis in synthetic organic chemistry for the year 2009. The continuing interest in lipases as catalysts for quantitative asymmetric transformation has resulted in their application to the synthesis of norsertraline and imidacloprid using dynamic kinetic resolution approaches. A lipase has also been used for the resolution of a complex dynamic compound library based on the reversible Strecker reaction. Esterases have been engineered for wider substrate specificity, and, in one case, to acquire epoxide hydrolase activity. A fluorophosphatase has been engineered to display activity toward the more toxic enantiomer of the nerve agent sarin. A new process has been formulated for the laccase-dependent regeneration of NAD(P)H for use in reductase-catalysed processes. Laccases themselves are attracting increasing interest as mild oxidation catalysts for aromatic coupling reactions leading to polycyclic biologically active compounds and dyes. An amino acid residue in enoate reductases has been highlighted as a major factor in determining enantioselectivity in those enzymes. In carbon–carbon bond formation, aldolases that are able to accept the non-phosphorylated C3 donor dihydroxyacetone have been applied to the synthesis of iminosugars, and the first application of the enzymatic Friedel-Crafts reaction has been realised. Last, aminomutases have found application in the synthesis of β-amino acids, in one case being combined with alanine racemase, furnishing an elegant process for the quantitative conversion of α-phenylalanine to its β-isomer.