The Study of Structure—Analgesic Activity Relationships in a Series of 4-Hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxylic Acid Toluidides and Xylidides

In continuing the search for new analgesics among derivatives of 2,1-benzothiazines, a series of corresponding toluidides and xylidides of 4-hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxylic acid has been synthesized by the reaction of ethyl 4-hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxylate with equimolar amounts of mono- and dimethyl-substituted anilides in boiling dry xylene. Their structure has been confirmed by the data of elemental analysis, nuclear magnetic resonance (NMR) spectroscopy ((1)Н and (13)С), as well as mass spectrometry. All compounds obtained were subjected to pharmacological screening to identify their analgesic properties. Testing was carried out in male rats using the standard model of the thermal tail-flick (tail immersion test) in parallel and in comparison with the structurally related drugs meloxicam and piroxicam. Among the substances studied, highly active oral painkillers have been found; they exceed the analgesic effect of the reference drugs using the same dose. Interesting structural and biological regularities have been described; they will be useful in further research on creating promising new analgesics based on 4-hydroxy-2,2-dioxo-1H-2λ(6),1-benzothiazine-3-carboxamides.