2-Сycloalkyl-(hetaryl-)-[1,2,4]triazol[1,5-с]quinazolines: synthesis, physical and chemical properties and antibacterial activity
Authors: Schabelnyk K. P. , Kholodnyak S. V. , Polishchuk N. M. , Kоvalenko S. І. 
Published: December 2020

In spite of the achievements in the chemistry of triazoloquinazolines, the synthetic possibilities of this class of compounds are not exhausted, some problems remain unresolved and require further study. 2-R-[1,2,4]triazolo[1,5-с]quinazolines are among them due to insufficiently explored but at the same time interesting in both chemical and biological aspects.
Undoubtedly «pharmacophore» has the crucial role in the response of a biological action. It is contained in this heterocycle namely the substitute position 2.
In view of the above, we attempted to modify triazolo[1,5-с]quinazoline by introducing a methyl group or halogens (fluorine, chlorine, bromine) into a benzene moiety and a triazole moiety of a cycloalkyl or heterocyclic substituent molecule.
The aim of this work is to develop simple and affordable methods of the synthesis of new 2-cycloalkyl-(hetaryl-)-[1,2,4]triazolo[1,5-с]quinazolines, quinazolines, to study their physical and chemical properties and to conduct primary screening for antibacterial activity
The antimicrobial activity of the synthesized chemical compounds was performed by the method of two-fold serial dilutions in Mueller–Hinton broth (for strains of Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853) and in Saburo broth (for Candida albicans ATCC 885–653). MIC (minimum inhibitory concentration), MBсC and MFсC (minimum bactericidal and fungicidal concentrations respectively) was determined.
The optimal method of synthesis of 2-cycloalkyl-(hetaryl-)-[1,2,4]triazolo[1,5-с]quinazolines, which represent value as chemical reagents for further transformations and study of biological activity is substantiated and developed. The possibility of «one-pot» synthesis of the target compounds with 4-hydrazinoquinazolines and cycloalkylcarboxylic acids under conditions of activation of the carboxyl group N,N¢-carbonyldiimidazole is shown. Conducted microbiological screening of 2-cycloalkyl-(hetaryl-)-[1,2,4]triazolo[1,5-с]quinazolines revealed a number of promising compounds that inhibit the growth of St. aureus (МІС 25‒50 μg/ml) and C. albicans (25‒50 μg/ml).
The optimal method of synthesis of 2-cycloalkyl-(hetaryl-)-[1,2,4]triazolo[1,5-с]quinazolin by cyclocondensation (3Н-quinazoline-4-ylidene)­hydrazides withcycloalkyl-(hetaryl)carboxylic acidsis substantiated and developed. The structure and individuality of the synthesized compounds were confirmed by elemental analysis, physicochemical methods (1H NMR-spectroscopy, HPLC/MS). The peculiarity of the 1H NMR spectra of this heterocycle is discussed, namely the significant paramagnetic shift of benzene protons and the characteristic weak-field single-proton singlet of the proton of position 5 of the heterocycle, which is a confirmation of recycling isomerization by Dimrot rearrangement. The structure-activity relationship is discussed and the study of the most active compounds for a wider range of strains and resistant strains of bacteria and fungi is recommended.