Biocatalytic Deracemization of 1,4‐Benzodiazepines in the Synthesis of Enantiomerically Pure Serine

An efficient stereocontrolled synthesis of (S)‐N‐Cbz‐serine (Cbz = benzyloxycarbonyl; 12) and of its (R)‐enantiomer is reported. Kinetic resolution of the easily available racemic 3‐(hydroxymethyl)‐1,4‐benzodiazepin‐2‐ones is performed in the key step via acetylation by the immobilized Mucor miehei lipase (Lipozyme IM) at 60°. This method is characterized by high enantiomer purity (ee's ges; 99%) of the intermediary alcohols (+)‐8 and (+)‐9 and acetates (−)‐10 and (−)‐11, as well as of the final products (S)‐ and (R)‐N‐Cbz‐serine, simple recycling of the biocatalyst, complete recovery of 2‐aminobenzophenones (3 and 4) and their recycling into production of 1,4‐benzodiazepines, and possibility to selectively racemize ‘wrong’ enantiomers of the alcohols 8 and 9 in the presence of Amberlite CG 400.