(4s) -3 - [(2s) -2 [(1s) -1- ethoxycarbonyl-3-phenylpropyl] amino propanoyl] -1-methyl-2-oxo-imidazole-4-carboxylic acid preparation

The present invention provides a (4S) -3 - [(2S) -2 [(1S) -1- ethoxycarbonyl-3-phenylpropyl] amino propanoyl] -1-methyl-2-oxo-imidazole the method of preparing 4-carboxylic acid, in particular, said method comprising: reacting a compound of formula (III) with a compound of formula (IV), to give a compound of formula (V). The method of the present invention is low cost, short route, raw materials, high yield and high optical purity.