Asymmetric Phase Transfer Catalytic Synthesis Of L-phenylalanine

N-(diphenylmethylene) glycine ethyl ester was synthesized from glycine ethyl ester hydrochloride and benzophenone. L-Phenylalanine was then obtained by alkylation of N-(diphenylmethylene) glycine ethyl ester with benzyl bromide in the presence of an asymmetric phase-transfer catalyst (+)-N-benzyl-cinchonine chloride, followed by hydrolysis of the resulting product. On the basis of this process, better results were obtained by using benzaldehyde in place of benzophenone and improving process conditions. The overall yield of the product phenylalanine was increased from 5.6% to 43.3%, and the value of enantiomeric excess of L-phenylalanine was reached to 63%. The results showed that the improved process has certain theoretic and practical value. Furthermore, the asymmetric alkylation mechanism induced by the chiral phase-transfer catalyst (+)-N-benzyl-cinchonine chloride was discussed and the effects of reaction factors such as the kinds of base, reaction solvents, temperature and reaction time on the enantioselective of the reaction were studied.