Synthesis of (R)- or (S)-valinol using ω-transaminases in aqueous and organic media

Abstract

Valinol is part of numerous pharmaceuticals and has various other important applications. Optically pure valinol (ee >99%) was prepared employing different ω-transaminases from the corresponding prochiral hydroxy ketone. By the choice of the enzyme the (R)- as well as the (S)-enantiomer were accessible. Reductive amination was performed in organic solvent (MTBE) using 2-propyl amine as amine donor whereas alanine was applied in or in aqueous medium. Transformations in phosphate buffer were successfully performed even at 200mM substrate concentration (20.4g/L) leading to 99% (R) and 94% (S) conversion with perfect optical purity (>99% ee).