O-Methyl isourea disulfate (I) is condensed with 4-aminomethylbenzoic acid (II) in 2 N NaOH solution to produce the corresponding guanidine, which is isolated as the hydrochloride salt (III). (1,2)
Esterification of 4'-hydroxybiphenyl-4-carboxylic acid (IV) with MeOH in the presence of H2SO4 produces the methyl ester (V), which is further transesterified with 4-methylbenzyl alcohol (VI) under basic conditions to generate the corresponding methylbenzyl ester (VII). Phenol (VII) is finally coupled with 4-(guanidinomethyl)benzoic acid (III) by means of DCC/pyridine to yield the target guanidino diester. (1,2)