Cyclization of itaconic acid (I) with 3-nitroaniline (II) at 100 C gives rise to 1-(3-nitrophenyl)-5-oxopyrrolidine-3-carboxylic acid (III). Subsequent condensation of acid (III) with methyl 3-amino-3-(3,5-dichlorophenyl)propanoate (IV) in the presence of EDC and HOAt yields amide (V). Reduction of the nitro group of (V) to the corresponding amine (VI) is effected by means of Zn and HOAc. Amine (VI) is then condensed with the cyclic thiourea (VII) employing HgCl2 to furnish the di-Boc-protected guanidine (VIII). Saponification of the methyl ester function of (VIII) then gives acid (IX). The N-Boc groups of (IX) are finally removed by treatment with trifluoroacetic acid to furnish the title compound.