Chiral synthesis of LSD1 inhibitor GSK2879552 enabled by directed evolution of an imine reductase

Imine reductases catalyse the reductive amination of aldehydes or ketones with amines to produce chiral amines—a key transformation in the preparation of fine chemicals and active pharmaceutical ingredients. Although significant progress has been recently made in the field, their industrial application has not been demonstrated. Herein, we describe a wild-type imine reductase that was engineered to perform reductive amination with concomitant substrate amine resolution to give a commercially relevant manufacturing process to lysine-specific demethylase-1 inhibitor GSK2879552. Three rounds of evolution resulted in an enzyme variant showing a >38,000-fold improvement over wild type. The engineering of a more stable and active enzyme variant enabled process optimization to an economic, high quality and sustainable operating space. Using the evolved enzyme, kilogram quantities of a key intermediate to GSK2879552 were produced in 84% yield, at 99.9% purity and >99.7% enantiomeric excess, with improved process mass intensity. Imine reductases have been regarded as one of the most promising enzymes by the pharmaceutical industry—but their industrial application is still lacking. This work reports the successful industrial application of an imine reductase, enabled by directed evolution.