One-Pot Enantioselective Synthesis of D-Phenylglycines from Racemic Mandelic Acids, Styrenes, or Biobased L-Phenylalanine via Cascade Biocatalysis

摘要

Enantiopure D-phenylglycine and its derivatives are an important group of chiral amino acids with broad applications in thepharmaceutical industry. However, the existing synthetic methods for D-phenylglycine mainly rely on toxic cyanide chemistry and multistep processes. To provide green and safe alternatives, we envisaged cascade biocatalysis for the one-pot synthesis of D-phenylglycine from racemic mandelic acid, styrene, and biobased l-phenylalanine, respectively. Recombinant Escherichia coli (LZ110) was engineered to coexpress four enzymes to catalyze a 3-step reaction in one pot, transforming mandelic acid (210 mM) to give enantiopure D-phenylglycine in 29.5 gL(-1) (195 mM) with 93% conversion. Using the same whole-cell catalyst, twelve other D-phenylglycine derivatives were also produced from the corresponding mandelic acid derivatives in high conversion (58-94%) and very high ee (93-99%). E. coli (LZ116) expressing seven enzymes was constructed for the transformation of styrene to enantiopure D-phenylglycine in 80% conversion via a one-pot 6-step cascade biotransformation. Twelve substituted D-phenylglycines were also produced from the corresponding styrene derivatives in high conversion (45-90%) and very high ee (92-99%) via the same cascade reactions. A nine-enzymeexpressing E. coli (LZ143) was engineered to transform biobased l-phenylalanine to enantiopure D-phenylglycine in 83% conversion via a one-pot 8-step transformation. Preparative biotransformations were also demonstrated. The high-yielding synthetic methods use cheap and green reagents (ammonia, glucose, and/or oxygen), and E. coli whole-cell catalysts, thus providing green and useful alternative methods for manufacturing D-phenylglycine.