Development of a Biocatalytic Process as an Alternative to the (−)-DIP-Cl-Mediated Asymmetric Reduction of a Key Intermediate of Montelukast

A KetoREDuctase (KRED) engineered via directed evolution technologies catalyzed the asymmetric reduction of (E)-methyl 2-(3-(3-(2-(7-chloroquinolin-2-yl)vinyl)phenyl)-3-oxopropyl)benzoate to the corresponding (S)-alcohol, a key intermediate in the synthesis of montelukast sodium (Singulair). Through synergistic efforts in process chemistry, molecular biology, bioinformatics and high throughput screening, a KRED with very high enantioselectivity (>99.9% ee) was developed for an economical and simple process that takes advantage of the physical properties of the substrate and product. The evolved KRED is an efficient and robust enzyme for catalyzing the reaction of an essentially water insoluble substrate (c log P ≈ 7) at a 100 g/L loading in the presence of ∼70% organic solvents at 45 °C. The biocatalytic process currently runs at >200 kg scale.