Preparation of L-phenylalanine with two newly-synthesized recoverable cinchonidine quaternary ammonium salt catalysts
AIM: To synthesize two novel cinchonidine quater-nary ammonium salt chiral catalysts and to apply them in the prep-arstion of L-phenylalanine (L-phe). METHODS: Two new chiral quaternary salts were prepared from cinchona alkaloids and 2-chloromethyl benzimidazole or 1-chloromethyl benzotriazole. The chiral phase transfer catalysts were tested in enantioselective alkylation of N-(diphenylmethylene) glycine t-butyl ester to syn-thesize (S)-α-benzyl-N-(diphenylmethylene) glycine t-butyl es-ter, and L-phe was then obtained with hydrolysis. After reaction, the chiral phase transfer catalysts were recovered with the help of diethyl ether. RESULTS: The yields of the ehiral phase transfer catalysts were 90% and 81%. The yields and enantiomeric excess values of (S) -α-benzyl-N-(diphenylrnethylene) glycine t-butyl ester were respectively 75%-91% and 90%-99%, and the total yields of L-phenylalanine was 41%-53%. The recovery rates of the catalysts were 75%-80%. CONCLUSION: Two novel cinchonidine quaternary ammonium salt catalysts are used in the asymmetric alkylation of N-(diphenylmethylene) glycine t-butyl ester and are recovered and reused. L-phenylalanine is prepared after the hydrolysis of (S)-α-benzyl-N-(diphenylmethylene) glycine t-butyl ester.
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