11-Dimethylaminomethyl-3, 4-dihydro-6-oxo-2H, 6H-1, 3-thiazino [3, 2-b] isoquinoline (IVa) and 11-formyl-3, 4-dihydro-6-oxo-2H, 6H-1, 3-thiazino [3, 2-b] isoquinoline (VI) were synthesized by Mannich reaction and Vilsmeier reaction of 3, 4-dihydro-6-oxo-2H, 6H-1, 3-thiazino [3, 2-b] isoquinolone (I), respectively. 6-Oxo-4H, 6H-1, 3-thiazino [3, 2-b] isoquinoline (XIb) was synthesized from 2-acetoxy-3, 4-dihydro-6-oxo-2H, 6H-1, 3-thiazino [3, 2-b] isoquinoline (IXb) upon treatment with p-tolenesulfonic acid, which was prepared by the Pummerer reaction of I. Reaction of 3, 4-dihydro-6-oxo-2H, 6H-1, 3-thazino [3, 2-b] isoquinoline-1, 1-dioxide (III) with alkyl halides gave monoalkylated (XIII) and dialkylated derivatives (XIV). The anti-inflammatory activity of these compounds was tested by the rat carrageenin paw edema method. IXa, b and VI showed stronger activity than phenylbutazone.
