Method for preparing N-[1-(S)-carbethoxy-3-hydrocinnamyl] -L-alanine-N-carboxy acid anhydride

One of the following formula (I) is N- [1- (S) - carbethoxy-3-phenylpropyl] -L- amino acid carboxy anhydride -N- manufacturing method: It is N- [1- (S) - carbethoxy-3-phenylpropyl] -L- amino acid of formula (V), XCOOR reaction, where X is a halogen atom and R lines C1-C6 alkyl, alkyl ester group formed N- ( after N-alkoxycarbonyl) compound, then reacted with an acid activating agent, with the final effect of water was added. The compounds of formula (I) for the synthesis of vasopressin converting enzyme (ACE) inhibitors. Method of the present invention has low toxicity, low risk and ease of operation.