L-tryptophyl-l-methionyl-l-aspartyl-l-phenylalanine amide - - n-protected derivs prepn

L-Tryptophanyl-L-methionyl-L-aspartyl-L-phenylalanine amide (I) having a protecting gp. on the amino residue (useful as a gastric secretion stimulant) is produced by (a) condensing 3-(benzyloxycarbonylmethyl)-aziridinone (II) having a protecting gp. on the imino residue with L-phenylalanine amide; (b) removing the amino-protecting gp. and the benzyl gp. from the resulting dipeptide; (c) condensing the resulting L-aspartly-L-phenylalanine amide (III) with 3-(2-methylthioethyl)-aziridinone (IV) having a protecting gp. on the imino residue; (d) removing the protecting gp. from the resulting tripeptide, and (e) condensing the resulting prod. with 3-(3-indolylmethyl)-aziridinone (V) having a protecting gp. on the imino residue, or by carrying out steps (a) and (b) above, then (f) condensing the resulting (III) with L-tryptophanyl-L-methionine azide having a protecting gp. on the amino residue prepd. by condensation of (V) having a protecting gp. on the imino residue with a methionine ester and conversion of the prod. into an azide. The processes give high yields of prod. of high purity and are suitable for large scale operation.