Reaction of 1-amino-4-methoxy-2,3,5-trimethylbenzene (I) with potassium thiocyanate and bromine in acetic acid gives 2-amino-6-methoxy-4,5,7-trimethylbenzothiazole (II), which is treated with 4-sulfamoylbenzoyl chloride [formed in situ from 4-sulfamoyl benzoic acid (III) and SOCl2], to afford 4-[N-(6-methoxy-4,5,7-trimethylbenzothiazol-2-yl)carbamoyl] benzenesulfonamide (IV). Compound (IV) is reduced with lithium aluminum hydride in tetrahydrofuran to yield 4-(6-methoxy-4,5,7-trimethylbenzothiazol-2-ylaminomethyl) benzenesulfonamide (V), which is finally demethylated with boron tribromide in methylene chloride.