Please cite this article as: Nikitina PA, Peregudov AS, Koldaeva TY, Kuz'mina LG, Adiulin EI, Tkach II, Perevalov VP, Synthesis and study of prototropic tautomerism of 2-(2-hydroxyphenyl)-1-hydroxyimidazoles, Tetrahedron (2015), Novel 2-(2-hydroxyphenyl) substituted imidazoles have been synthesized. A prototropic tautomerism of the 1-hydroxyimidazole derivatives has been studied. X-ray diffraction analysis and IR-spectroscopy have revealed that in the solid state the title compounds exist as the Nhydroxy tautomers. The 1 H and 13 C NMR spectra of the new imidazole derivatives are discussed. It has been shown that in chloroform solutions 5-carbonylsubstituted 2-(2-hydroxyphenyl)-1-hydroxyimidazoles exist in the N-hydroxy tautomeric form. A transition to DMSO results in the existence of the 1-hydroxyimidazoles under study as the N-oxide tautomers.

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Novel 2-(2-furyl)imidazole derivatives were synthesised. 2-(2-Furyl)-1-methoxyimidazoles and 2-(2-furyl)-1-methylimidazole 3-oxides were used as model compounds in the study of the prototropic tautomerism of 2-(2-furyl)-1-hydroxyimidazoles by means of 1H, 13C NMR and UV/vis spectroscopies. It was demonstrated that the interaction of the π-excessive furyl moiety with an electron-withdrawing carbonyl group in position 5 of imidazole stabilised the N-hydroxy tautomeric form in both deuterated chloroform and d6-DMSO. In ethanol the N-oxide tautomer is also present along with the prevailing N-hydroxyimidazole.

Prototropic tautomerism of 2-(3-chromenyl)-1-hydroxyimidazoles with various substituents in the chromenyl moiety (1-hydroxyimidazole – imidazole N-oxide) was studied by means of 1H NMR and IR spectroscopies. It was demonstrated that in d6-DMSO solution, the substituents in the chromenyl ring have no influence on the equilibrium shift: the prevalence of the N-oxide tautomeric form is caused by the possibility of stabilization of the planar structure with the help of the carbonyl group in position 5 of the imidazole ring. In contrast, in the solid state the general effect of the chromenyl substituent in position 2 of imidazole plays the leading role. The increase in general electron-withdrawing effect of the chromenyl moiety leads to the prevalence of the imidazole N-oxide tautomer.

Angiotensin-converting enzyme 2 (ACE2), the functional receptor of SARS-CoV-2, plays a crucial role in the pathogenesis of COVID-19. ACE2 targeting holds the promise for preventing and inhibiting SARS-CoV-2 infection. In this work, we describe the development and use of a test system based on competitive ELISA for the primary screening of potential antiviral compounds. We studied the activity of the library of dyes of different groups. Several dyes (ortho-cresolphthalein, eosin (free acid), eosin (Na salt)) that inhibited the interaction of ACE2 with the spike proteins of SARS-CoV-2 have been identified among the candidates. A potential antiviral drug, methylene blue, did not show activity in our study. We believe that our results can help in the further search for inhibitors of interaction between the coronavirus spike protein and ACE2 receptor.