To a mixture of 2-methyl-3-[methyl(2-thienylsulfonyl)amino]-4H-thieno[3,2-b]pyrrole-5-carboxylic acid (0.35 g), 2-(tritylthio)ethaneamine hydrochloride (0.43 g), 1H-1,2,3-benzotriazol-1-ol (0.19 g), triethylamine (0.2 mL) and N,N-dimethylformamide (10 mL) was added N-[3-(dimethylamino)propyl]-N′-ethylcarbodiimide hydrochloride (0.23 g), and the mixture was stirred at room temperature overnight. Water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with saturated brine, dried (MgSO4) and concentrated to give a colorless oil. To a solution of triphenylphosphine oxide (0.83 g) in dichloromethane (20 mL) was slowly added trifluoromethanesulfonic anhydride (0.25 mL) at 0° C., the mixture was stirred for 10 min. The colorless oil was added to the mixture and the mixture was stirred at room temperature for 3 hr and concentrated. Saturated aqueous sodium hydrogen carbonate was added, and the mixture was extracted with ethyl acetate. The ethyl acetate layer was washed with saturated brine, dried (MgSO4) and concentrated. The residue was subjected to silica gel column chromatography to give N-[5-(4,5-dihydro-1,3-thiazol-2-yl)-2-methyl-4H-thieno[3,2-b]pyrrol-3-yl]-N-methylthiophene-2-sulfonamide (111 mg, yield 29%) as colorless crystals from a fraction eluted with ethyl acetate-hexane (1:20→1:1, volume ratio). melting point 140° C.
