INTRODUCTION:An analysis of the literature on the painkillers long used in traditional medicine, which are isolated from plant materials, has shown that many of them are alkylamides of various carboxylic acids. This fact served as the basis for the study of a large group of N-alkyl-4- methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides as potential new analgesics. The objects of the study were synthesized in the traditional way involving the initial conversion of 4-methyl- 2,2-dioxo-1H-2λ6,1- benzothiazine-3-carboxylic acid to imidazolide, in which imidazolide was used as an acylating agent. The method is simple to implement and, as a rule, gives high yields of final alkylamides. However, in reaction with sterically hindered tert-butylamine, along with the "normal" product, an unexpected formation of N-tert-butyl-4-methyl-1-(4-methyl-2,2-dioxo-1H-2λ6,1- benzothiazine-3-carbonyl)-2,2-dioxo-2λ6,1-benzothiazine-3-carboxamide was observed, which was characterized by X-ray diffraction analysis as a monosolvate with N,N-dimethylformamide. These synthetic problems can be avoided using a more powerful acylating agent, 4-methyl-2,2-dioxo-1H- 2λ6,1- benzothiazine-3-carbonyl chloride.BACKGROUND:A large group of new N-alkyl-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3- carboxamides was synthesized.OBJECTIVE:On the basis of molecular docking, some derivatives of N-alkyl-4-methyl-2,2-dioxo-1H- 2λ6,1-benzothiazine-3-carboxamides have been designed. Their preliminary structure-activity relationships (SAR) have been studied. The most rational approaches to the synthesis of lead compounds have been developed. The most active compounds have shown high anti-inflammatory and analgesic activities.METHODS:The structure of all compounds prepared has been confirmed by the data of elemental analysis, 1H- and 13C NMR spectroscopy, and electrospray ionization liquid chromato-mass spectrometry. For rational drug design, optimization of further pharmacological screening and prediction of a possible mechanism of pharmacological action, molecular docking has been performed. For the determination of activity, pharmacological studies have been carried out.RESULTS:Pharmacological tests have determined that the transition from N-aryl(heteroaryl) alkylamides to "pure" N-alkylamides we carried out is accompanied by a significant reduction and even complete loss of anti-inflammatory effect with remaining analgesic activity.CONCLUSION:According to the studies, compounds from N-alkyl-4-methyl-2,2-dioxo-1H-2λ6,1- benzothiazine-3-carboxamides are potential anti-inflammatory and analgesic agents.

The title benzothiazine-3-carboxamide, C17H16N2O4S, crystallized in two enantiomorphic crystal forms with the space groups P32 and P31 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.

In order to study polymorphic modifications of N-(4-trifluoromethylphenyl)-4-hydroxy-2,2-dioxo-1H-2λ6,1-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: “acetic-acid-induced writhing”, “hot plate”, “thermal irritation of the tail tip” (tail-flick), “tail electric stimulation” and “neuropathic pain”), 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-2λ6,1-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.

The title mol­ecule crystallizes as a di­methyl­formamide monosolvate, C19H14N2O6S2·C3H7NO. The mol­ecule was expected to adopt mirror symmetry but slightly different conformational characteristics of the condensed benzo­thia­zine ring lead to point group symmetry 1. In the crystal, mol­ecules form two types of stacking dimers with distances of 3.464 (2) Å and 3.528 (2) Å between π-systems. As a result, columns extending parallel to [100] are formed, which are connected to inter­mediate di­methyl­formamide solvent mol­ecules by C—H⋯O inter­actions.

In order to detect new structural and biological patterns in a series of hetaryl-3-carboxylic acid derivatives, the optically pure (S)- and (R)-enantiomers of N-(1-arylethyl)-4-methyl- 2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides, their true racemates, and mechanical racemic mixtures have been synthesized in independent ways. The particular features of the 1Н- and 13С-NMR spectra of all synthesized substances, liquid chromato-mass spectrometric behavior thereof under electrospray ionization conditions, and also the results of polarimetric and X-ray diffraction studies have been discussed. Pharmacological screening on a model of carrageenan inflammation has found a clear relationship between the spatial structure of the studied objects and biological activity thereof. Enantiomers with chiral centers having (S)-configuration showed weak inhibition of pain and inflammatory reactions, while their mirror (R)-isomers exhibited very powerful analgesic and antiphlogistic properties under the same conditions, with the level of specific activity exceeding that of Lornoxicam and Diclofenac. Taking obtained data into account, a noticeable decrease in the activity of mechanical racemic mixtures, consisting of one-half of the “wrong” (S)-enantiomers, is quite natural. The true racemate of N-(1-phenylethyl)-amide proved itself in a similar way, while 4-methoxy-substituted analog thereof stood out against this background with unexpectedly high analgesic and anti-inflammatory activities. A comparative analysis of X-ray diffraction data has found that crystalline and molecular structure of racemic N-[1-(4-methoxyphenyl)ethyl]-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamide is completely different from that of the original enantiomers and, moreover, very unusual for racemates. Obviously, it is the factor determining the unique character of the biological effects of the said substance.

The title molecule crystallizes as a dimethylformamide monosolvate, C19H14N2O6S2·C3H7NO. The molecule was expected to adopt mirror symmetry but slightly different conformational characteristics of the condensed benzothiazine ring lead to point group symmetry 1. In the crystal, molecules form two types of stacking dimers with distances of 3.464 (2) Å and 3.528 (2) Å between π-systems. As a result, columns extending parallel to [100] are formed, which are connected to intermediate dimethylformamide solvent molecules by C—H...O interactions.

According to our quantum and chemical calculations 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylic acid imidazolide is theoretically almost as reactive as its 2-carbonyl analog, and it forms the corresponding N-pyridyl-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides with many aminopyridines. However, in practice, the sulfo group introduces significant changes at times and prevents the acylation of sterically hindered amines. One of these products was 2-amino-6-methylpyridine. Thus, it has been concluded that aminopyridines interact with imidazolide in aromatic form where the target for the initial electrophilic attack is the ring nitrogen. To confirm the structure of all substances synthesized, 1H-NMR spectroscopy and X-ray diffraction analysis were used. From X-ray diffraction data it follows that in the crystalline phase the carbonyl and sulfo group may occupy different positions with respect to the plane of the benzothiazine bicycle: this position may be unilateral, typical for 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides, versatile, and not yet encountered in compounds of this type. A comparison of these data with the results of the pharmacological screening conducted on the standard model of carrageenan inflammation showed that the N-pyridylamides of the first group demonstrated a direct dependence of their analgesic and anti-inflammatory activity on the mutual arrangement of the planes of the benzothiazine and pyridine fragments. The new molecular conformation of the benzothiazine nucleus provides a sufficiently high level of analgesic (but not anti-inflammatory) properties in all N-pyridylamides of the second group with an extremely weak dependence on the spatial arrangement of the pyridine cycle. All substances presented this article proved themselves in varying degrees as analgesics and antiphlogistics. Moreover, two of them—N-(5-methylpyridin-2-yl)- and N-(pyridin-3-yl)-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides—exceeded the most effective drug of oxicam type Lornoxicam by these indicators.

In accordance with the principles of “me-too” technique, the preparative method for obtaining has been proposed, and the synthesis of a large series of new N-(arylalkyl)-6-hydroxy-2-methyl-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]quinoline-5-carboxamides as structurally close analogs of tricyclic pyrrolo- and pyridoquinoline diuretics has been carried out. All target compounds were obtained with high yields and purity by amidation of ethyl ester of the corresponding 2-methyl-pyrroloquinoline-5-carboxylic acid with arylalkylamines in boiling ethanol. Their structure was confirmed by the data of elemental analysis, nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and polarimetry. Moreover, interpretations of their 1H and 13C-NMR spectra, their mass spectrometric behavior, as well as peculiarities of the polarimetric studies were discussed. The effect of N-(arylalkyl)-6-hydroxy-2-methyl-4-oxo-2,4-dihydro-1H-pyrrolo[3,2,1-ij]quinoline-5-carboxamides on the urinary function of the kidneys was studied in white rats by the standard method of oral administration in the dose of 10 mg/kg compared to hydrochlorothiazide. According to the results of the primary pharmacological screening, the structural and biological regularities that were unexpected, but interesting for further studies were revealed. Among the substances studied, the samples, which by their diuretic effect are not inferior and even superior to both the known hydrochlorothiazide and the lead structure of the pyrroloquinoline group, have been found. On this basis, it can be argued that the introduction of the methyl group made by us in position 2 of pyrrolo[3,2,1-ij]quinoline nucleus can be considered as a successful and promising implementation of the “me-too” cloning of tricyclic 4-hydroxyquinoline-2-one diuretics.

The analysis of our previous studies on the search for synthetic analgesics among N-R-amides of bicyclic hetaryl-3-carboxylic acids has been performed; on its basis N-hetaryl(aryl)-alkyl-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides have been selected as new study objects. The “one pot synthesis” of these compounds, which is simple to perform and at the same time highly effective, has been offered. The method consists in the initial reaction of 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylic acid and N,N′-carbonyldiimidazole in anhydrous N,N-dimethylformamide with the subsequent amidation of imidazolide formed with hetarylalkyl- or benzylamines in the same solvent. The peculiarities of 1H- and 13C-NMR spectra of the substances obtained, as well as their electrospray ionization liquid chromato-mass spectra are discussed. According to the results of the pharmacological tests carried out on the model of carrageenan inflammation it has been found that all without exception N-hetaryl(aryl)alkyl-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides demonstrate the statistically significant analgesic and anti-inflammatory properties. Among the substances presented in this article analgesics and antiphlogistics, which increase the pain threshold and suppress the inflammatory response more effectively than Lornoxicam and Diclofenac in the same doses, have been identified. The molecular and crystal structures of a large group of the substances synthesized have been studied by X-ray diffraction analysis. Comparison of these data with the results of biological tests has revealed the fact of excellent correlation between the molecular conformations of N-hetaryl(aryl)alkyl-4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides recorded in the crystal and the potency of their analgesic effect. N-Thiophen-2-ylmethyl- and N-4-methoxybenzyl-amides of 4-methyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylic acid has shown a high analgesic and anti-inflammatory effect, therefore, they deserve more careful research.

With the aim of establishing a structure-analgesic activity relationship, a series of picolylamides of 2-hydroxy-4-oxo-4H-pyrido[1,2-a]-pyrimidine-3-carboxylic acids were synthesized. The characteristics of the spatial structure of this group of substances were assessed. The results of pharmacological studies identified compounds in the study series with marked analgesic properties. However, it was noted that the transition from 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxamides to the structurally similar pyrido[1,2-a]pyrimidine derivatives was generally accompanied by some decrease in analgesic activity.

С целью установления закономерностей связи «структура — анальгетическая активность» осуществлен синтез серии пиколиламидов 2-гидрокси-4-оксо-4H-пиридо[1,2-a]-пиримидин-3-карбоновых кислот. Обсуждаются особенности пространственного строения данной группы веществ. По результатам проведенных фармакологических испытаний среди изученных соединений выявлены образцы с выраженными обезболивающими свойствами. Однако отмечается, что переход от близких по строению 4-гидрокси-2-оксо-1,2-дигидрохинолин-3-карбоксамидов к пиридо[1,2-a]пиримидиновым производным в целом сопровождается некоторым спадом анальгетической активности.

In continuation of the search for new biologically active substances in a series of 4-hydroxy-2,2-dioxo-1 H -2λ 6 ,1-benzothiazine-3-carboxamides, a series of {[(4-hydroxy-1-methyl-2,2-dioxido-1 H -2,1-benzothiazin-3-yl)carbonyl]amino}benzoic acids and their derivatives at the carboxy group have been synthesized. According to the results of pharmacological studies, it is established that compounds with a free carboxy group are of interest as potential diuretics and carbamide derivatives are promising as analgesics, while esterification of the carboxy group with lower alkyl alcohols is less effective.

В продолжение поиска новых биологически активных веществ в ряду 4-гидрокси-2,2-диоксо-1H-2λ6,1-бензотиазин-3-карбоксамидов осуществлен синтез серии {[(4-гидрокси-1-метил-2,2-диоксидо-1H-2,1-бензотиазин-3-ил)карбонил]амино}бензойных кислот и их производных по карбоксильной группе. По результатам фармакологических испытаний установлено, что соединения со свободной карбоксильной группой представляют интерес в качестве потенциальных диуретиков, а карбамидные производные перспективны как анальгетики. Этерификация карбоксильной группы низшими алкиловыми спиртами менее эффективна.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Methyl-4-hydroxy-1-phenyl-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxylate was found to undergo transesterification even during crystallization from EtOH to convert into the corresponding ethyl ester. The molecular structure of the obtained compound was studied. In particular, PMR spectroscopy and x-ray crystal structure analysis established that the 1-N-phenyl substituent was situated in solution at an angle of ~60° to the plane formed by the aminophenylcarbinol fragment of the 2,1-benzothiazine whereas this angle increased to 80° in the crystal because of packing effects.

Дальневосточный государственный медицинский университет Обнаружено, что метил-4-гидрокси-1-фенил-2,2-диоксо-1H-2λ6,1-бензотиазин-3-карбоксилат способен вступать в реакцию переэтерификации уже при кристаллизации из этилового спирта, превращаясь при этом в соответствующий этиловый эфир. Изучены особенности пространственного строения полученного соединения. В частности, с помощью спектроскопии ЯМР 1H и рентгеноструктурного анализа установлено, что в растворе 1-N-фенильный заместитель расположен под углом около 60° к плоскости, образованной аминофенилкарбинольным фрагментом 2,1-бензотиазина, тогда как в кристалле за счет эффектов упаковки этот угол возрастает до 80°.

Дальневосточный государственный медицинский университет Обнаружено, что метил-4-гидрокси-1-фенил-2,2-диоксо-1H-2λ6,1-бензотиазин-3-карбоксилат способен вступать в реакцию переэтерификации уже при кристаллизации из этилового спирта, превращаясь при этом в соответствующий этиловый эфир. Изучены особенности пространственного строения полученного соединения. В частности, с помощью спектроскопии ЯМР 1H и рентгеноструктурного анализа установлено, что в растворе 1-N-фенильный заместитель расположен под углом около 60° к плоскости, образованной аминофенилкарбинольным фрагментом 2,1-бензотиазина, тогда как в кристалле за счет эффектов упаковки этот угол возрастает до 80°.

Continuing the search for novel biologically active substances among the 4-hydroxy-2,2-dioxo-1H-2λ6,1-benzothiazine-3-carboxamides series, we report here the synthesis of a series of {[(4-hydroxy-1-methyl-2,2-dioxido-1H-2,1-benzothiazin-3-yl)carbonyl]amino} benzoic acids asd their derivatives at the carboxyl group. Pharmacological testing showed that compounds with a free carboxyl group are of interest as potential diuretics, while carbamide derivatives have potential as analgesics. Esterification of the carboxyl group with lower alkyl alcohols was less effective.