Coupling of N-benzylpyroglutamic acid (I) with 4-nitrophenylalanine methyl ester (II) by means of O-benzotriazolyl-N,N,N?N?tetramethyluronium hexafluorophosphate (HBTU) produced amide (III). After stannous chloride mediated reduction of the nitro group of (III), the resulting aniline (IV) was coupled with 2,6-dichlorobenzoic acid (V) to give diamide (VI). The title carboxylic acid was then obtained by ester hydrolysis with NaOH.