This compound can be obtained by two related ways: 1) The solid-state photodimerization of ethyl 3,4-dimethoxycinnamate (I) gives the corresponding dimeric cyclobutane (II), which is hydrolyzed with KOH in methanol yielding the corresponding diacid (III). The reaction of (III) with 4-[N2,N3-bis(tert-butoxycarbonyl)-N3-(3-methyl-2-butenyl)guanidino]butylamine (IV) by means of CMC and Ts-OMe affords the protected diamide (V), which is finally deprotected with methanesulfonic acid. 2) The solid-state photodimerization of benzyl 3,4-dimethoxycinnamate (VI) gives the corresponding dimeric cyclobutane (VII), which is debenzylated by hydrogenation with H2 over Pd/C yielding the previously described diacid (III).