Two pseudo-enantiomeric forms of N-benzyl-4-hydroxy-1-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamide and their analgesic properties

The fact that molecular crystals exist as different polymorphic modifications and the identification of as many polymorphs as possible are important considerations for the pharmaceutic industry. The molecule of N-benzyl-4-hydroxy-1-methyl-2,2-dioxo-1H-2 lambda(6),1-benzothiazine-3-carboxamide, C17H16N2O4S, does not contain a stereogenic atom, but intramolecular hydrogen-bonding interactions engender enantiomeric chiral conformations as a labile racemic mixture. The title compound crystallized in a solvent-dependent single chiral conformation within one of two conformationally polymorphic P2(1)2(1)2(1) orthorhombic chiral crystals (denoted forms A and B). Each of these pseudo-enantiomorphic crystals contains one of two pseudo-enantiomeric diastereomers. Form A was obtained from methylene chloride and form B can be crystallized from N,N-dimethylformamide, ethanol, ethyl acetate or xylene. Pharmacological studies with solid-particulate suspensions have shown that crystalline form A exhibits an almost fourfold higher antinociceptive activity compared to form B.