Alkylation of ethyl 4-chloroindole-2-carboxylate (I) with ethyl 5-bromovalerate (II) in the presence of NaH in DMF afforded diester (III). Regioselective hydrolysis of the aliphatic ester group employing sulfuric acid and acetic acid at 75 C produced the mono-carboxylic acid (IV). The intramolecular cyclization of acid (IV) by means of phosphoric acid and phosphorus pentoxide furnished the tricyclic system (V). The ethyl ester group of (V) was then treated with guanidine (VI) to yield the target acyl guanidine derivative, which was finally converted to the title methanesulfonate salt.