The alkylation of 2-(methylsulfanyl)benzothiazole (I) with methyl p-toluenesulfonate in anisole gives 3-methyl-2-(methylsulfanyl)benzothiazolium p-toluenesulfonate (II), which is condensed with 3-ethyl-2-thioxothiazolidin-4-one (III) by means of triethylamine in acetonitrile to yield 3-ethyl-5-(3-methyl-2,3-dihydrobenzothiazol-2-ylidene)-2-thioxothiazolidin-4-one (IV). The methylation of (IV) with methyl p-toluenesulfonate in DMF affords 3-ethyl-5-(3-methyl-2,3-dihydrobenzothiazol-2-ylidene)-2-(methylsulfanyl)-4-oxo-4,5-dihydrothiazolium p-toluenesulfonate (V) (1), which is condensed with 1-ethyl-2-methylpyridinium p-toluenesulfonate (VI) by means of triethylamine in warm acetonitrile giving the p-toluenesulfonate of MKT-077 (VII). Finally, this compound is passed through an ion-exchange resin (Amberlyst A-26) in methanol/chloroform.
N-Methylation of 2-(methylsulfanyl)benzothiazole (I) using methyl p-toluenesulfonate afforded iminium salt (II), which was condensed with 3-ethyl-4-oxothiazolidine-2-thione (III) to give the benzothiazolinylidene dervative (IV). Subsequent S-methylation of (IV) to produce the 3-ethyl-2-(methylthio)thiazolinium salt (V) was followed by condensation with 2,4-dimethyl-3-ethylthiazolium salt (VI) in the presence of Et3N, yielding the triheterocyclic system (VIII) as the p-toluenesulfonate salt. Finally, conversion to the title chloride salt was achieved by means of an anionic exchange resin.