N-Boc-D-(3-phenylpropyl)glycine (I) was esterified to benzyl ester (II), and then, tert-butoxycarbonyl group was cleaved by acidic treatment to give amine (III). This was coupled with N-Boc-2-aminoisobutyric acid (IV) in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide.HCl (EDC) and 1-hydroxybenzotriazole (HOBt) to afford dipeptide ester (V), from which the benzyl ester group was removed by hydrogenolysis in the presence of Pd/C. The resulting acid (VI) was condensed with 1-(2-nitrophenyl)piperazine (VII) in the presence of EDC and HOBt to produce piperazide (VIII). Subsequent reduction of the nitro group by hydrogenation in the presence of Raney-Ni gave aniline (IX), which was treated with 2-propanesulfonyl chloride (X) to yield sulfonamide (XI). Finally, the tert-butoxycarbonyl protecting group was removed by treatment either with HCl in EtOAc or with trifluoroacetic acid to afford the target compound as the hydrochloride or the trifluoroacetate salt, respectively.