4-Hydroxy-1-(3-methyl-butyl)-2-oxo-1,2-dihydro-pyrrolo[1,2-b]pyridazine-3-carboxylic acid ethyl ester (Example 1f, 0.040 g, 0.14 mmol) was mixed with 2-amino-5-methoxy-benzenesulfonamide (Example 2b, 0.0235 g, 0.14 mmol) and the resulting mixture was heated to 180° C. for 20 min. The resulting crude oil was allowed to cool to 25° C. and ethanol (0.5 mL) was added and sonicated to afford a tan precipitate, which was collected and dried in vacuo. The crude solid was dissolved in 1.0 M aqueous potassium hydroxide solution (0.5 mL) and heated to 110° C. for 12 h. The reaction mixture was allowed to cool to 25° C. and 10% aqueous hydrochloric acid solution (0.5 mL) was added and the resulting white precipitate was collected. The crude solid was washed with methanol and dried in vacuo to afford the desired product, 4-hydroxy-3-(7-methoxy-1,1-dioxo-1,4-dihydro-1λ6-benzo[1,2,4]thiadiazin-3-yl)-1-(3-methyl-butyl)-pyrrolo[1,2-b]pyridazin-2-one (0.027 g, 0.063 mmol, 47% yield) as a white solid. 1H NMR (400 MHz, DMSO-d6) δ 1.07 (6H, d, J=6.4 Hz), 1.69 (1H, m), 1.78 (1H, m), 3.89 (3H, s), 4.39 (2H, t, J=7.6 Hz), 6.60 (1H, dd, J1=4.4 Hz, J2=2.8 Hz), 7.04 (1H, d, J=4.4 Hz), 7.05 (1H, dd, J1=4.8 Hz, J2=2.0 Hz), 7.25 (1H, m), 7.17 (1H, m), 7.39 (1H, d, J=2.0 Hz); LC-MS (ESI) calcd for C19H22N4O5S 430.49. found 431.33 [M+H+].
