Coupling of N-Cbz-tyrosine (I) with n-pentylamine (II) afforded amide (III). Subsequent alkylation of the phenol group of (III) with diethyl chloromalonate (IV) gave phenoxy malonate (V). Hydrogenolytical deprotection of the N-Cbz group of (V) provided the corresponding amine, which was isolated as the hydrochloride salt (VI). Conversion of (VI) to isocyanate (VII) was effected by treatment with diphosgene in the presence of Proton Sponge(r). Addition of phenylalanine ethyl ester (VIII) to isocyanate (VII) furnished urea (IX). Finally, the ethyl ester groups of (IX) were saponified with LiOH to yield the title compound.

3-Iodo-L-tyrosine (I) was protected as the N-Boc derivative (II) and subsequently coupled to n-pentylamine yielding amide (III). Palladium-catalyzed carboxylation of the aryl iodide of (III) in the presence of MeOH afforded the methyl ester (IV). The phenolic hydroxyl group of (IV) was then alkylated with methyl bromoacetate under basic conditions to produce diester (V). Acidic Boc group cleavage in (V), followed by acylation of the resulting amine (VI) with N-Boc-L-phenylalanine (VII), generated the dipeptide derivative (VIII). Further deprotection of (VIII) with HCl in dioxane yielded amine (IX), which was finally coupled with succinic acid mono-methyl ester (X) to provide the title compound.