Efficient Production of L-Homophenylalanine by Enzymatic-Chemical Cascade Catalysis.

L-Homophenylalanine (L-HPA) is a vital building block for the synthesis of numerous chiral drugs. However, the high cost of starting materials limits the industrial production of L-HPA. In this study, an enzymatic-spontaneous chemical cascade route for L-HPA production was designed based on retrosynthetic analysis. This route, using simple benzaldehyde and pyruvate as starting materials, is extremely cost-effective. The enzymes were screened and further assembled in E. coli, and TipheDH was identified as the rate-limiting enzyme. Therefore, TipheDH was engineered to improve its specific activity (by 82 %) and expression level (by 254 %), thus generating the best strain (W14). W14 exhibited the optimum enzyme activity ratio (1.7 : 1.1 : 1 : 1.8) and demonstrated production of 100.9 g L of L-HPA (with 94 % conversion, >99 % ee) in a 5-L reactor. This route effectively exploits the power of cascades and offers insight into avenues for synthesizing other valuable chemicals from inexpensive building blocks.