Abstract: A process for preparing .alpha.-L-aspartyl-L-phenylalanine methyl ester consisting of:bringing N-formyl-L-aspartic anhydride and L-phenylalanine methyl ester, in a molar ratio equal or approximately equal to 1:1, into contact with a solid cation exchange resin having free sulphonic, phosphonic or carboxylic acid groups, the ration of the acid equivalents of said resin acid groups to the number of moles of the one or other reagent being equal to or less than about 1:1, and operating in the liquid phase in an inert organic solvent at a temperature of about 40.degree. C. or less, until a mixture of N-formyl-.alpha.-L-aspartyl-L-phenylalanine methyl ester and N-formyl-.beta.-L-aspartyl-L-phenylalanine methyl ester forms in which the .alpha. isomer prevails over the .beta. isomer;deformylating said N-formyl-.alpha.-L-aspartyl-L-phenylalanine methyl ester and N-formyl-.beta.-L-aspartyl-L-phenylalanine methyl ester; andseparating and recovering the .alpha.

Abstract: A process for preparing .alpha.-L-aspartyl-L-phenylalanine methyl ester: ##STR1## in which: (a) the compound methyl N(.alpha.-L-aspartyl).alpha.-aminocinnamate, protected at the nitrogen, of formula: ##STR2## where R is a protector group at the nitrogen, is subjected to hydrogenation at the olefin bond by means of gaseous hydrogen in the presence of a hydrogenation catalyst, to give the compound of formula: ##STR3## where R has the aforesaid meaning, in the form of a mixture of .alpha.-L-aspartyl-L-phenylalanine methyl ester protected at the nitrogen, and .alpha.-L-aspartyl-D-phenylalanine methyl ester protected at the nitrogen;(b) the protector group is removed from the .alpha.-L-aspartyl-L-phenylalanine and .alpha.-L-aspartyl-D-phenylalanine methyl esters protected at the nitrogen;(c) the .alpha.-L-aspartyl-L-phenylalanine methyl ester is separated and recovered from the deprotection reaction product.