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A study of two polymorphic forms of 1-allyl-4-hydroxy-2,2-dioxo-N-(4-methoxyphenyl)-1-2λ6,1-benzothiazine-3-carboxamide (a structural analogue of piroxicam) has revealed some regularities in the crystal structure formation due to different evaporation rates from the tested solvents. The monoclinic polymorph crystallized from ethyl acetate is formed due to a large number of very weak C—H...O and C—H...π interactions as well as one strong stacking interaction. The triclinic polymorph crystallized from N,N-dimethylformamide is formed due to a small number of weak specific interactions and a maximal number of strong stacking interactions. The stacked dimer is a complex building unit in both polymorphic structures. Further analysis showed that the monoclinic structure is layered while the triclinic one is columnar. The two polymorphic structures also differ in their biological activity (antidiuretic and analgesic). The monoclinic polymorph possesses very high biological activity while the triclinic polymorph is almost inactive. The polymorphic transition of the biologically active metastable monoclinic structure into the inactive stable triclinic one within four weeks of grinding is caused by orientational factors rather than conformational ones and is accompanied by a change in the redistribution of interaction energies in the crystal from anisotropic to more isotropic. Thus, a slow polymorphic transition after grinding results in a loss of the biological activity.

A study of two polymorphic forms of 1-allyl-4-hydroxy-2,2-dioxo-N-(4-methoxyphenyl)-1-2λ

The title benzothiazine-3-carboxamide, C

In order to study polymorphic modifications of N-(4-trifluoromethylphenyl)-4-hydroxy-2,2-dioxo-1H-2&lambda, 6,1-benzothiazine-3-carboxamide, which is of interest as a promising analgesic, its three colorless crystal forms with different habitus have been obtained: sticks of ethyl acetate, plates of meta-xylene and blocks of ortho-xylene. However, the X-ray diffraction analysis has shown that all the forms studied have the identical molecular and crystal structure in spite of such significant differences in appearance. Moreover, pharmacological tests have revealed significant differences in the analgesic activity in these samples (a total of five experimental models were used: &ldquo, acetic-acid-induced writhing&rdquo, &ldquo, hot plate&rdquo, thermal irritation of the tail tip&rdquo, (tail-flick), &ldquo, tail electric stimulation&rdquo, and &ldquo, neuropathic pain&rdquo, ), acute toxicity and the ability to cause gastric damage. As a result, only the plate crystal form of N-(4-trifluoromethylphenyl)-4-hydroxy-2,2-dioxo-1H-2&lambda, 6,1-benzothiazine-3-carboxamide is recommended for further studies. Thus, it has been proven that the habitus of crystals is an important characteristic of the drug substance and is able to have a noticeable effect on its biological properties. Changes in habitus should be considered as a guide to the mandatory verification of at least the basic pharmacological parameters of the new form regardless of whether the molecular and crystal structure changes.