Engineering of Cascade Reactions and Alditol Oxidase for High‐Yielding Synthesis of (R)‐Phenylethanolamine from Styrene, l‐Phenylalanine, Glycerol or Glucose

Abstract

(R)‐phenylethanolamine (PEA) is a useful and valuable chiral chemical and requires enantioselective and efficient synthesis method. A novel SMO‐StEH‐AldO‐CvTA‐catalyzed cascade reaction was established to convert styrene to (R)‐PEA via epoxidation‐hydrolysis‐oxidation‐amination. The key transformation of (R)‐1‐phenyl‐1,2‐ethanediol to (R)‐PEA in the cascade was achieved in 94 % conversion via AldO‐CvTA. The limiting enzyme AldO was engineered through directed evolution, yielding a mutant AldO(MVIK) with 3‐fold enhanced catalytic efficiency. The use of AldO(MVIK) in the 4‐enzyme cascade significantly increased the productivity than the use of AldO, yielding 34.6 mM (R)‐PEA with >99 % ee. By incorporating deamination and decarboxylation enzymes, a 6‐enzyme cascade was engineered to produce 23.7 mM (R)‐PEA from l‐phenylalanine. Coupling of l‐phenylalanine biosynthesis pathway with 6‐enzyme cascade enabled synthesis of (R)‐PEA from glycerol or glucose, producing 6.8 mM and 6.5 mM (R)‐PEA, respectively. The developed cascade biotransformations provide direct synthesis of (R)‐PEA from either simple chemicals or renewable feedstocks.

Cascade Biotransformations for Enantioconvergent Conversion of Racemic Styrene Oxides to (R)-Mandelic Acids

“…The epoxide hydrolase from Solanum tuberosum (StEH) was identified for enantioconvergent hydrolysis of rac - 1a to ( R )-phenyl-1,2-ethanediol 2a ; it catalyzes the conversion of rac - 1a to ( R )- 2a in about 90% ee . To ensure a high final product ee , a quadruple mutant of the alditol oxidase from Streptomyces coelicolor (Aldo­(M)) with high enantioselectivity toward ( R )- 2a was selected for oxidizing the terminal hydroxyl group of ( R )- 2a . Although Aldo­(M) also catalyzes the further oxidation of ( R )-mandelaldehyde 3a to ( R )- 4a , this reaction is too slow; reactive ( R )- 3a accumulating in the reaction can undergo side reactions.…”