To a solution of 272 (18.9 mg, 0.027 mmol) dissolved in dichloromethane (1 mL) was added trifluoroacetic acid (100 μl) and triethylsilane (200 μl). The reaction mixture was stirred at room temperature for ½ hours under an inert atmosphere then concentrated in vacuo. The residue was triturated with diethyl ether/hexane (1/1) to afford 2-acetylamino-4-methyl-thiazole-5-sulfonic acid 7-(4-fluoro-benzyl)-9-hydroxy-8-oxo-7,8-dihydro-6H-pyrrolo[3,4-g]quinolin-5-yl ester 273, TFA salt, (13.2 mg, 74%) as a yellow solid: 1H NMR (CD3OD) δ 8.9 (d, 1H), 8.2 (d, 1H), 7.6 (m, 1H), 7.4 (m, 2H), 7.1 (t, 2H), 4.7 (s, 2H), 4.4 (s, 2H), 2.23 (s, 3H), 2.21 (s, 3H); MS: 543 (M+1).
