A New Protocol for Catalyst-Free Regioselective Synthesis of 5,9-Dihydropyrimido[5,4-e][1,2,4]triazolo[1,5-a]pyrimidine-6,8(4H,7H)-diones

Dihydroazolopyrimidines: Past, Present and Perspectives in Synthesis, Green Chemistry and Drug Discovery

Dihydroazolopyrimidines are an important class of heterocycles that are isosteric to natural purines and are therefore of great interest primarily as drug-like molecules. In contrast to the heteroaromatic analogs, synthetic approaches to these compounds were developed much later, and their chemical properties and biological activity have not been studied in detail until recently. In the review, different ways to build dihydroazolopyrimidine systems from different building blocks are described - via the initial formation of a partially hydrogenated pyrimidine ring or an azole ring, as well as a one-pot assembly of azole and azine fragments. Special attention is given to modern approaches: multicomponent reactions, green chemistry, and the use of non-classical activation methods. Information on the chemical properties of dihydroazolopyrimidines and the prospects for their use in the design of drugs of various profiles are also summarized in this review.

Strategies for synthesis of 1,2,4-triazole-containing scaffolds using 3-amino-1,2,4-triazole

1,2,4-Triazole-containing scaffolds are unique heterocyclic compounds present in an array of pharmaceuticals and biologically important compounds used in the drug-discovery studies against cancer cells, microbes, and various types of disease in the human body. This review article summarizes the pharmacological significance of the 1,2,4-triazole-containing scaffolds and highlights the latest strategies for the synthesis of these privileged scaffolds using 3-amino-1,2,4-triazole. This review stimulates further research to find new and efficient methodologies for accessing new 1,2,4-triazole-containing scaffolds which would be very useful for the discover of new drug candidates.

A three-component cyclocondensation reaction for the synthesis of new triazolo[1,5-a]pyrimidine scaffolds using 3-aminotriazole, aldehydes and ketene N,S-acetal

This study describes the use of 3-aminotriazole, different aldehydes and N-methyl-1-(methylthio)-2-nitroethenamine as a ketene N,S-acetal in a three-component condensation for the synthesis of a novel library of triazolo[1,5-a]pyrimidine scaffolds. The presence of trichloroacetic acid as a Brønsted-Lowry acidic promoter in acetonitrile or water solvent and room temperature condition resulting novel triazolo[1,5-a]pyrimidine systems named N-methyl-6-nitro-5-aryl-3,5-dihydro-[1, 2, 4]triazolo[1,5-a]pyrimidine-7-amine. The structure of products and direction of the N-cyclization could be confirmed using spectral data. The effect of various solvents on the progress of process was investigated in the paper. The presence of five nitrogen heteroatoms, the use of various aldehydes affording a range of skeletally distinct triazolo[1,5-a]pyrimidine-based heterocycles, the potency to create numerous hydrogen bonds in the product structure, and direction of cyclization are attractive features of this reaction.

Synthesis and evaluation of anti-tumor activity of novel triazolo[1,5-a] pyrimidine on cancer cells by induction of cellular apoptosis and inhibition of epithelial-to-mesenchymal transition process

Cancer is a leading cause of human death worldwide. One of the greatest challenges in cancer therapy is the discovery and design of novel products with potential anti-tumor activities. In this study, a new protocol involves three-component condensation of the 3-amino-1,2,4-triazole as a 1,3-binucleophile, versatile aldehydes and N-methyl-1-(methylthio)-2-nitroethenamine as an enamine analogous in the presence of trichloroacetic acid as a Brønsted-Lowry acidic promoter leads to new functionalized N-alkyl-6-nitro-3,5-dihydro-[1,2,4]triazolo[1,5-a]pyrimidin-7-amine in moderate to good yields. The presence of five nitrogen heteroatoms in the product structure has gathered immense attention among chemists and biologists due to their biological values. Therefore, we evaluated the anti-tumor activity of our synthetic compounds on different cancer cells including human malignant melanoma cells (A375), prostate cancer cells (PC3 cells, LNCaP cells) and normal cells HDF (human dermal fibroblast). Notably, we found that compound 4b that contains a nitro group has the best anti-tumor activity on three different cancer cells. By using DAPI staining, we showed cancer cells death. Apoptosis induction was shown using quantitative real time PCR (qRT-PCR) by evaluating of Bax and Bcl2 mRNA levels. Finally, we demonstrated that 4b has epithelial-to-mesenchymal transition (EMT) inhibition effect on cancer cells (by induction of E-cadherin and reduction of vimentin mRNA expression levels as two potential EMT markers). So, 4b could be an anti-cancer promising drug. Although, in vivo experiments will be required to evaluate possible side effects.

A novel protocol for catalyst-free synthesis of fused six-member rings to triazole and pyrazole

Herein, an effectual, quick and novel method is described for the synthesis of new triazolo[1,5-a]pyrimidine, triazolo[5,1-b][1,3] thiazine and pyrazolo[1,5-a]pyrimidine derivatives. This series of fused six-member rings to triazole and pyrazole was prepared via the catalyst-free reaction of dialkyl acetylenedicarboxylates and 3-substituted 1H-1,2,4-triazole or 3-amino-1H-pyrazole-4-carbonitrile. The structures of the prepared products were deduced from their Fourier-transform infrared, elemental analysis and proton and carbon-13 nuclear magnetic resonance spectral data. A novel and green method is described for the synthesis of new triazolo[1,5-a]pyrimidine, triazolo[5,1-b][1,3] thiazine and pyrazolo[1,5-a]pyrimidine derivatives.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.