Reaction of methyl 6-nitroindole-2-carboxylate (I) with ethylenediamine (II) in hot DMF gives amino amide (III). After protection of (III) as the N-Boc derivative (IV), catalytic hydrogenation of its nitro group affords amine (V). Indole-2,5-dicarboxylic (VI) is activated as the bis-pentafluorophenyl ester (VII) by treatment with pentafluorophenyl trifluoroacetate. Subsequent coupling between the bis-pentafluorophenyl ester (VII) and amino indole (V) furnishes diamide (VIII). Removal of the N-Boc groups using trifluoroacetic acid in the presence of anisole produces diamine (IX).

Coupling of diamine (IX) with the Boc-protected diamino acid (X) by means of DCC and HOBt gives rise to amide (XI). The title compound is finally obtained by acidic cleavage of the N-Boc protecting groups of (XI).