7-R-Amino-6-(tetrazol-5-yl)azolo[1,5-a]pyrimidines as Potential CK2 Inhibitors: Synthesis and Cytotoxic Activity

Objective: The structure of 6-(tetrazol-5-yl)azolo[1,5-a]pyrimidines as inhibitors of casein kinase 2 (CK2) has been optimized by the replacement of the primary C7-amino group with a secondary amino fragment to increase the affinity for the active site of CK2. The proposed water-soluble heterocycles have been obtained by original synthetic scheme, which involved exploiting the NH-acidity of the tetrazole ring. The cytotoxic activity of the obtained water-soluble derivatives of 6-(tetrazol-5-yl)azolopyrimidines was studied on several cell lines, including cells with overexpression of CK2, lung carcinoma A-549 and hepatocellular carcinoma Hep-G2. Methods: An original synthetic scheme with the construction of a condensed azaheterocyclic system, chlorodeoxygenation, nucleophilic substitution of a halogen atom, and the azide-nitrile cycloaddition. The structure and purity of obtained heterocycles were confirmed by a suite of modern physico-chemical methods of analysis. Cytotoxicity was studied by MTT assay. Results and Discussion: It was shown that 7-oxoazolopyrimidine-6-carbonitriles could be constructed by reaction of aminoazoles and ethyl 2-cyano-3-ethoxyacrylate through intermediate enamine compounds. Further chlorodeoxygenation and nucleophilic substitution of chlorine atom in situ resulted in 7-R-aminoazolopyrimidin-6-carbonitriles. The latter were used as the substrates for azide-nitrile cycloaddition to give desired 6-(tetrazol-5-yl)azolopyrimidines. The cytotoxicity of water-soluble sodium salts of these molecules was studied on different tumor cells as well as pseudo-normal cells HEK-293. Conclusions: It was found that most 7-R-amino-6-(tetrazol-5-yl)azolo[1,5-a]pyrimidines exhibited a weak effect on the viability of tumor cells, probably, a special impact is required to induce programmed cell death in addition to inhibiting CK2. Sodium 5-(2-(benzylthio)-7-((4-chlorophenethyl)amino)-[1,2,4]triazolo[1,5-a]pyrimidin-6-yl)tetrazol-2-id demonstrated the greatest cytotoxicity against liver carcinoma cells with an IC50 index < 39.66 µmol/L.