Water → 3-Oxo-3,4-dihydro-2H-pyrido[3,2-b][1,4]thiazine-6-carboxylic acid

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Reaction Steps

A solution of Methyl 3-oxo-3,4-dihydro-2H-pyrido[3,2-b][1,4]thiazine-6-carboxylate (788 mg) in dioxane (120 ml)/water (30 ml) was treated dropwise over 2 hours with 0.5M NaOH solution (8 ml) and stirred overnight. After evaporation to approx. 3 ml, water (5 ml) was added and 2N HCl to pH=4. The precipitated solid was filtered off, washed with a small volume of water and dried under vacuum to give a solid (636 mg). MS (APCl−) m/e 209 ([M−H]−, 5%),165([M-COOH]−, 100%).

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