Abstract: A process is described for the synthesis of N-protected-L-.alpha.-aspartyl-L-phenylalanine by both (a) the rection of an N-protected-L-aspartic anhydride and a R.sub.1 -L-phenylalanine, and (b) the reaction of an N-protected-L-aspartic anhydride and L-phenylalanine in an aqueous medium in the presence of R.sub.2, where R.sub.1 may be an alkali metal salt, alkaline earth metal salt, ammonium salt or organic amine salt, and R.sub.2 may be an ammonium salt or an alkali or alkaline earth metal salt of an inorganic or organic acid.

Abstract: A process is described for the synthesis of N-protected-L-.alpha.-aspartyl-L-phenylalanine by both (a) the reaction of an N-protected-L-aspartic anhydride and a R.sub.1 -L-phenylalanine, and (b) the reaction of an N-protected-L-aspartic anhydride and L-phenylalanine in an aqueous medium in the presence of R.sub.2, where R.sub.1 may be an alkali metal salt, alkaline earth metal salt, ammonium salt or organic amine salt, and R.sub.2 may be an ammonium salt or an alkali or alkaline earth metal salt of an inorganic or organic acid.

Abstract: The invention relates to a process for producing N-protected-.alpha.L-aspartyl-L-phenylalanine methyl ester, which comprises esterifying L-phenylalanine with methanol in the presence of a strong acid catalyst, adding, to the resulting solution, an aqueous alkaline solution to neutralize the acid catalyst and a water-immiscible organic solvent to extract the free L-phenylalanine methyl ester thus formed, collecting the organic layer, and reacting the L-phenylalanine methyl ester dissolved in said collected organic layer with N-protected-L-aspartic anhydride.

Abstract: A method for converting .beta.-aspartylphenylalanine derivative (1) to .alpha.-aspartylphenylalanine derivatives (2) and (3), said derivatives having the following structures: ##STR1## which comprises: reacting said .beta.-aspartylphenylalanine derivative (1) at a temperature of from 0.degree. to 200.degree. C. for a time period of from 30 minutes to 80 hours, in a C.sub.1 to C.sub.4 alcohol solvent with or without stirring, wherein R and R' represent hydrogen or an alkyl group having from 1 to 4 carbon atoms.