To a solution of (Z)-2-[(6-carboxyindol-3-yl)methylene]-2H-1,4-benzothiazin-3(4H)-one (0.5 g, 1.5 mmol) in dry N,N-dimethylformamide (30 ml), 1,1′-carbonyldiimidazol (0.24 g, 1.5 mmol) was added under nitrogen atmosphere, and the mixture was heated at 40° C. for 1 h. Then N-(2-aminoethyl)pyrrolidine (0.34 g, 2.98 mmol) was added and the mixture heated at the same temperature for an additional time of 20 h. The reaction was allowed to cool to room temperature and the solvent removed under reduced pressure. The residue was treated with water and the yellow precipitate was crystallized from N,N-dimethylformamide/water to yield 0.31 g (48%) of the entitled product.
