Heterocyclizations based on N-(R-hydrazine-1-carbonothioyl)cycloalkancarboxamides: functionalized azoles and their antimicrobial activity

Abstract

Synthesis and structural modification of azoles remains an important area of medical chemistry and allows to obtain new compounds with a wide range of biological activity. Among the significant number of azoles, 1,3,4-thiadiazoles and 1,2,4-triazoles attract special attention, among which are known drugs, larvicides, insecticides, growth regulators, etc. Even though heterocyclizations of functionally substituted hydrazines for their synthesis are well studied, N-(R-hydrazine-1-carbonothioyl)cycloalkanecarboxamides, and nowadays, remain reagents with undiscovered potential. Moreover, the introduction of lipophilic “pharmacophore” fragments (cycloalkanes) in the structure of 1,3,4-thiadiazoles and 1,2,4-triazoles is a promising direction for their modification. That should provide additional intermolecular interactions with enzymes and may lead to enhancement or alteration of the biological activity vector. Thus, the synthesis of new derivatives of this class of compounds and the study of their antibacterial properties remains an urgent problem of medical and organic chemistry.

Aim. To investigate the heterocyclization of N-(R-hydrazine-1-carbonothioyl)cycloalkanecarboxa-mides, to establish the structure and antibacterial activity of the synthesized compounds.

Materials and methods. Methods of organic synthesis, physical and physical-chemical methods of analysis of organic compounds (NMR ¹H-spectroscopy, chromato-mass spectrometry, elemental analysis). The antimicrobial activity of the synthesized compounds was studied according to the generally accepted method for standard strains of microorganisms and fungi.

Results. The peculiarities of heterocyclization of N-(R-hydrazine-1-carbonothioyl)cycloalkanecarboxamides have been studied and the factors influencing this reaction have been elucidated. It was shown that these compounds under the conditions of the heterocyclization reaction in concentrated mineral acids form 5-R-2-amino-1,3,4-thiadiazoles. The intermediate undergoes additional hydrolysis by cleavage of the cycloalkanecarboxyl fragment. Alternative methods for the synthesis of 5-R-2-amino-1,3,4-thiadiazoles were proposed. For the first time, the original 4-cycloalkanecarbonyl-3-(amino-,phenyloxo-(thio)methyl-1,5-dihydro-4H-1,2,4-triazole-5-thiones were synthesized by prolonged heating of the corresponding disubstituted thiosemicarbazides. It was not possible to extend this reaction to other diacylthiosemicarbazides, the latter undergo heterocyclization in the presence of sodium hydroxide with the formation of the known 5-R-2,4-dihydro-3H-1,2,4-triazole-3-thiones. ¹H NMR spectra were studied, analyzed, and regularities of splitting of characteristic protons in functionalized azoles were established. Conducted microbiological screening was showed that 5-R-2-amino-1,3,4-thiadiazoles, 4-cycloalkanecarbonyl-3-(amino-,phenyloxo-(thio)methyl-1,5-dihydro-4H-1,2,4-triazole-5-thiones and 5-R-2,4-dihydro-3H-1,2,4-triazole-3-thione were less effective antibacterial and antifungal agents (MIC 100–200 μg/ml) compared with N-(R-hydrazine-1-carbonothioyl)cycloalkanecarboxamides (MIC 3.125–200 μg/ml).

Conclusions. It was found that N-(R-hydrazine-1-carbonotioyl)cycloalkane-carboxamides, depending on the conditions of heterocyclization form 5-R-2-amino-1,3,4-thiadiazoles, 3-(phenyloxo-(thio)methyl-1,5-dihydro-4H-1,2,4-triazole-5-thiones or 5-R-2,4-dihydro-3H-1,2,4-triazole-3-thiones. It was established that synthesized azoles were shown less effective antimicrobial and antifungal activity in comparison with N-(R-hydrazine-1-carbonothioyl)cycloalkanecarboxamides.