A 500-mL two-neck flask was charged with 5-bromo-N-(2,4-dimethoxybenzyl)-N-(1,2,4-thiadiazol-5-yl)naphthalene-2-sulfonamide (Intermediate D; 10 g, 19.22 mmol), palladium (ii) acetate (0.216 g, 0.961 mmol), and Xantphos (1.112 g, 1.922 mmol). Triethylamine (77 ml, 19.22 mmol), toluene (48.0 ml), and methanol (15.55 ml, 384 mmol) were added, and the reaction was fitted with a reflux condensor. The reaction was evacuated and back-filled with carbon monoxide three times, then the reaction was heated to 70° C. and stirred for four hours under an atmosphere of carbon monoxide. The reaction was filtered through a pad of diatomaceous earth, which was thoroughly washed with ethyl acetate. The filtrate was concentrated, triturated in ethyl acetate and filtered. The solids were collected and the filtrate was concentrated. The trituration procedure was repeated twice, and the solids resulting from each trituration were combined with the previously isolated material. After the third trituration, the mother liquor was purified via column chromatography (80 g silica gel column, gradient elution 0 to 50% EtOAc:Heptane). The clean product fractions were combined with the previously isolated material and the resulting slurry was concentrated to afford methyl 6-(N-(2,4-dimethoxybenzyl)-N-(1,2,4-thiadiazol-5-yl)sulfamoyl)-1-naphthoate as a light yellow solid. m/z (ESI) 500.3 (M+H)+. 60 mg of methyl 6-(N-(2,4-dimethoxybenzyl)-N-(1,2,4-thiadiazol-5-yl)sulfamoyl)-1-naphthoate was dissolved in 1 mL of DCM and TFA (0.1 ml, 1.298 mmol) was added. The reaction was stirred for 30 minutes at room temperature. The material was concentrated, dissolved in acetonitrile and loaded onto a Biotage Isolute® PEAX ion exchange column (Biotage AB, Uppsala, Sweden) (pre-wetted with acetonitrile). The column was flushed several times with acetonitrile, then the product was liberated by flushing the column several times with about 1M HCl solution in MeOH/EtOAc. The second filtrate was concentrated to afford methyl 6-(N-(1,2,4-thiadiazol-5-yl)sulfamoyl)-1-naphthoate. 1H NMR (400 MHz, DMSO-d6) δ ppm=8.90 (d, J=9.2 Hz, 1H), 8.60 (d, J=2.0 Hz, 1H), 8.53-8.44 (m, 2H), 8.29 (dd, J=1.3, 7.3 Hz, 1H), 7.96 (dd, J=2.1, 9.2 Hz, 1H), 7.76 (dd, J=7.3, 8.2 Hz, 1H), 3.95 (s, 3H). m/z (ESI) 350.1 (M+H)+.
