The reaction of 4-chloro-2-amino-1-nitrobenzene (I) with sodium phenylmercaptide (A) in DMF gives 2-amino-4-phenylthio-1-nitrobenzene (II), which is treated with acetic anhydride to yield 2-acetamido-4-phenylthio-1-nitrobenzene (III). This product is oxidized with peracetic acid in methanol giving 2-amino-4-phenylsulfinyl-1-nitrobenzene (V). Then the nitro group is reduced with H2 over Pd/C in methanol yielding 1,2-diamino-4-phenylsulfinylbenzene (VI). This product is finally condensed with N,N?bis(methoxycarbonyl)-S-methylisothiourea (VII) in ethanol - water - acetic acid. The isothiourea (VII) is obtained by reaction of S-methylisothiouronium sulfate (VIII) with methyl chloroformate (B) by means of KOH in water