4-Hydroxy-1-(3-methyl-butyl)-2-oxo-1,2-dihydro-pyrrolo[1,2-b]pyridazine-3-carboxylic acid ethyl ester (Example 1f, 0.218 g, 0.75 mmol) was dissolved in pyridine (1.5 mL) and 2-amino-5-iodo-benzenesulfonamide (Example 4a, 0.222 g, 0.75 mmol) was added. The reaction mixture was heated at 120° C. for 16 h, and then 1,8-diazabicyclo[5.4.0]undec-7-ene (0.12 mL, 0.78 mmol) was added an heated for another 4 h. The pyridine was removed in vacuo to afford the crude desired product. Purification by flash column chromatography (Merck silica gel 60, 40-63 μm, 5%-10% methanol in dichloromethane) afforded the desired product, 4-hydroxy-3-(7-iodo-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 (0.110 g, 0.209 mmol, 28% yield) as a white solid. LC-MS (ESI) calcd for C19H19IN4O4S, found 526.02, found 527.20 [M+H+].
