4H-pyrimido[1,2-b]pyridazine-2-carboxylic acid, 6,7-dihydro-4,7-dioxo-, methyl ester InChI=1/C9H7N3O4/c1-16-9(15)5-4-8(14)12-6(10-5)2-3-7(13)11-12/h2-4H,1H3,(H,11,13 methyl 4,7-dioxo-6,7-dihydro-4H-pyrimido[1,2-b]pyridazine-2-carboxylate