1,3-Diaminopropane (I) is mono-protected with benzyl chloroformate, producing carbamate (II). Coupling of (II) with N,N'-bis-Boc-S-methylisothiourea (III) yields the Boc-protected guanidine (IV). The benzyloxycarbonyl group of (IV) is then removed by catalytic hydrogenolysis to furnish the noragmatine derivative (V)

Coupling between N-Boc-D-(4-chlorophenyl)alanine succinimidyl ester (VI) and L-naphthylalanine methyl ester (VII) affords the protected dipeptide (VIII). The methyl ester group of (VIII) is hydrolyzed by means of LiOH to produce the carboxylic acid (IX), which is subsequently coupled to the di-Boc-protected noragmatine (V), yielding amide (X). Finally, acidic cleavage of the Boc protecting groups of (X) leads to the title compound