合成路线1

The intermediate aniline (IV) was synthesized by Mitsunobu coupling between N-Boc-4-piperidinol (I) and p-nitrophenol (II), followed by catalytic hydrogenation of the resultant nitrophenyl ether (III). 7-Formyl-2-naphthalenecarbonitrile (VI) was prepared by oxidation of the bromomethyl(naphthalene) (V) employing either trimethylamine N-oxide or dimethylsulfoxide in the presence of silver tetrafluoroborate. Reductive alkylation of aniline (IV) with aldehyde (VI) by means of sodium triacetoxyborohydride produced the secondary amine (VII), which was subsequently acylated with ethyl 2-(Chlorosulfonyl)acetate (VIII) to furnish sulfonamide (IX). The required amidine (X) was then obtained by Pinner reaction of nitrile (IX) with ethanolic HCl, followed by treatment with ammonium acetate. The deprotected piperidine moiety of (X) was further subjected to condensation with ethyl acetimidate to give the bis-amidine compound (XI). The ethyl ester group of (XI) was finally hydrolyzed under acidic conditions, yielding the target carboxylic acid.