Study of the Chemoselectivity of Multicomponent Heterocyclizations Involving 3-Amino-1,2,4-triazole and Pyruvic Acids as Key Reagents, and Biological Activity of the Reaction Products

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.

Nitronate-aryne cycloaddition as a concise route to stereochemically complex fused benzisoxazolines and amino alcohols

The reaction of cyclic nitronates (isoxazoline N-oxides and 5,6-dihydro-4H-1,2-oxazine N-oxides) with Kobayashi's aryne precursors affords tricyclic benzene-fused nitroso acetals as a result of [3 + 2]-cycloaddition. The process is regio- and stereoselective in most cases and produces the target cycloadducts possessing up to four contiguous stereogenic centers. These nitroso acetals were shown to be convenient precursors of valuable polysubstituted aminodiols through catalytic hydrogenolysis of the N-O bonds. Also, the action of protic acids resulted in an unusual fragmentation of the cyclic nitroso acetal moiety through heterolytic N-O bond cleavage and Beckmann-type reaction. Using this acid-mediated reaction, the synthesis of a hitherto unknown hexahydrobenzo[4,5]isoxazolo[2,3-a]azepine scaffold was accomplished.

N-tert-Butyl-2-{2-[2-(4-chloro-phen-yl)-4-hy-droxy-1-(5-methyl-isoxazol-3-yl)-5-oxo-2,5-di-hydro-1H-pyrrol-3-yl]-N-(4-meth-oxy-phen-yl)acetamido}-2-(4-meth-oxy-phen-yl)acetamide methanol monosolvate: single-crystal X-ray diffraction study and Hirshfeld surface analysis

The title compound, C36H37ClN4O7·CH3OH, which crystallizes as a methanol solvate, may possess biological activity, which is inherent for a natural peptide or protein. In the crystal, mol-ecules of the title compound form hydrogen-bonded tetra-mers with the solvate mol-ecules acting as bridges as a result of the O-H⋯O and N-H⋯O inter-molecular hydrogen bonds. Hirshfeld surface analysis was used to study the different types of inter-molecular inter-actions whose contributions are: H⋯H = 53.8%, O⋯H/H⋯O = 19.0%, C⋯H/H⋯C = 14.8%, Cl⋯H/H⋯Cl = 5.3%, N⋯H/H⋯N = 3.2%.

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.

Stereoselective, Multicomponent Approach to Quaternary Substituted Hydroindole Scaffolds

The Amaryllidaceae alkaloids have been a target of synthesis for decades due to their complex architectures and biological activity. A central feature of these natural product cores is a quaternary substituted hydroindole heterocycle. Building off the foundation of our previous multicomponent approach to highly functionalized pyrrolidinones, herein we report a highly convergent, diastereoselective, multicomponent approach to access the hydroindole cores present within crinine, haemanthamine, pretazettine, and various other bioactive alkaloids. These scaffolds are additionally useful as building blocks for druglike molecules and natural product like library generation.

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.

Ultrasonic-assisted unusual four-component synthesis of 7-azolylamino-4,5,6,7-tetrahydroazolo[1,5-a]pyrimidines

Four-component reactions of 3-amino-1,2,4-triazole or 5-amino-1H-pyrazole-4-carbonitrile with aromatic aldehydes and pyruvic acid or its esters under ultrasonication were studied. Unusual for such a reaction type, a cascade of elementary stages led to the formation of 7-azolylaminotetrahydroazolo[1,5-a]pyrimidines.

High-Performance Vapor-Phase Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate over SiO2 Supported PMoVNb Oxides

This paper describes the application of P-Mo-V-Nb/SiO2 catalysts for the selective oxidation of ethyl lactate (EL) to ethyl pyruvate (EP). The P-Mo-V-Nb/SiO2 catalysts exhibit superior performance for EP selectivity than the corresponding samples of binary V-Nb/SiO2 ternary P-Mo-V/SiO2 and P-Mo-Nb/SiO2 catalysts at same temperatures. The origin of high EP selectivity of the P-Mo-V-Nb/SiO2 catalysts is explored and attributed to the synergistic effect of P, Mo, V, and Nb mixed oxides presented on the surface of the catalyst. The highly dispersive sites separated active species under the action of phosphorus, suppressing over oxidation and improving the selectivity. The existence of MoO3 to provide higher oxidation for catalyst. The redox cycle of V and Nb oxides could be completed through electron transfer between lattice oxygen and metal cations. Moreover, the weak acidity of catalyst surface is favorable to avoid the decarboxylation reaction to target a high selectivity of EP. Therefore, the P-Mo-V-Nb/SiO2 catalyst obtained the maximum yield of 91.8% with a selectivity of 93.8% and a conversion of 99.0% simultaneously at 280 °C.

Doebner-type pyrazolopyridine carboxylic acids in an Ugi four-component reaction

Substituted 1H-pyrazolo[3,4-b]pyridine-4- and 1H-pyrazolo[3,4-b]pyridine-6-carboxamides have been synthetized through a Doebner-Ugi multicomponent reaction sequence in a convergent and versatile manner using diversity generation strategies: combination of two multicomponent reactions and conditions-based divergence strategy. The target products contain as pharmacophores pyrazolopyridine and peptidomimetic moieties with four points of diversity introduced from readily available starting materials including scaffold diversity. A small focused compound library of 23 Ugi products was created and screened for antibacterial activity.

Pyrazolo-fused 4-azafluorenones as key reagents for the synthesis of fluorescent dicyanovinylidene-substituted derivatives

A green method for the three-component synthesis of an indeno[1,2-b]pyrazolo[4,3-e]pyridines library under microwave irradiation and their use in the preparation of novel fluorescent dicyanovinylidene-substituted derivatives is provided.

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.

Heterocyclization Reactions of Pyruvic Acids and Aminoazoles with Controlled Chemoselectivity

The present review includes the analysis of known literature data concerning linear and multicomponent heterocyclizations involving pyruvic acids and aminoazoles. In particular, the review demonstrates the approaches to control regio- and chemoselectivity of these types of treatments and their application to solve the matters of Diversity Oriented Synthesis.