Biological properties of two enantiomorphic forms of N -(2,6-dimethylphenyl)-4-hydroxy-2,2-dioxo-1 H -2λ 6 ,1-benzothiazine-3-carboxamide, a structural analogue of piroxicam

The title benzothiazine-3-carboxamide, C 17 H 16 N 2 O 4 S, crystallized in two enantiomorphic crystal forms with the space groups P 3 2 and P 3 1 despite the absence of a classic stereogenic atom. The molecular structures are mirror images of each other. Only one sulfonyl O atom takes part in intramolecular hydrogen bonding as a proton acceptor and this atom is different in the two enantiomorphic structures. As a result, the S atom becomes a pseudo-stereogenic centre. This fact is worth taking into account due to the different biological activities of the enantiomorphic forms. One form possesses a high analgesic activity, while the other form revealed a high anti-inflammatory activity.