D-Alaninol (I) was protected as the tert-butyl carbamate (II) and then converted to mesylate (III). Displacement of the mesylate group of (III) with NaCN furnished nitrile (IV), which was hydrogenated over Raney Nickel to give diamine (V). Condensation of (V) with benzaldehyde (VI) in the presence of molecular sieves produced imine (VII) and subsequent reduction by means of NaBH4 gave rise to the benzyl amine (VIII). This amine was alkylated with 4-chlorobutyronitrile (IX) to afford nitrile (X), which was further converted to the triamino compound (XI) by hydrogenation over Raney Nickel. Reaction of (XI) with methyl 2-[(phenoxycarbonyl)oxy]acetate (XII) provided carbamate (XIII). The ester group of (XIII) was then hydrolyzed with NaOH to give carboxylic acid (XIV).

The resulting carboxylic acid (XIV) was coupled with the Boc-protected guanidinohexylamine (XV) using DCC and HOBt to produce amide (XVI). Finally, sequential deprotection of the N-benzyl group of (XVI) by hydrogenolysis, and then cleavage of the Boc groups by means of trifluoroacetic acid yielded the target compound.