Reconstructive Methodology in the Synthesis of 2-Aminopurine

A fundamentally new synthetic approach to the synthesis of 2-aminopurine has been developed. It consists in the combination of the creation of a condensed polyazotic heterocyclic tetrazolopyrimidine structure, its transformation into triaminopyrimidine, and its subsequent cyclization into 2-aminopurine. The structure of the obtained compounds was established based on spectral characteristics, and the structure of the intermediate compound 5 was established directly by X-ray diffraction analysis.

Synthesis and Assessment of Antiplatelet and Antithrombotic Activity of 4-Amino-Substituted 5-Oxoproline Amides and Peptides

Venous thromboembolism is a serious problem because it significantly increases the risk of developing vascular complications in elderly patients with obesity or immobilization, cancer, and many other diseases. Thus, there is a need to study new therapeutic strategies, including new medicinal agents for the efficient and safe correction of thrombus disorders. In this work, we have synthesized a number of new amides and peptides of 4-amino-5-oxoprolines and studied their antiplatelet and antithrombotic activity in experiments in vitro and in vivo. It has been found that the newly obtained compounds slow down the process of thrombus formation in a model of arterial and venous thrombosis, without affecting plasma hemostasis parameters. (2S,4S)-4-Amino-1-(4-fluorophenyl)-5-oxoprolyl-(S)-phenylalanine proved to be the most efficient among the studied derivatives. The results obtained indicate the advisability of further studies on 5-oxoproline derivatives in order to design pharmaceutical agents for the prevention and treatment of the consequences of thrombosis.

Exploring Three Avenues: Chemo- and Regioselective Transformations of 1,2,4-Triketone Analogs into Pyrazoles and Pyridazinones

A convenient approach to substituted pyrazoles and pyridazinones based on 1,2,4-triketones is presented. Chemo- and regiocontrol in condensations of t-Bu, Ph-, 2-thienyl-, and CO2Et-substituted 1,2,4-triketone analogs with hydrazines are described. The direction of preferential nucleophilic attack was shown to be switched depending on the substituent nature in triketone as well as the reaction conditions. The acid and temperature effects on the selectivity of condensations were revealed. Regiochemistry of heterocyclic core formation was confirmed by NMR and XRD studies. The facile construction of heterocyclic motifs bearing acetyl and (or) carbethoxy groups suggests them as promising mono- or bifunctional building blocks for subsequent transformations.

Perfluoroalkyl Chain Length Effect on Crystal Packing and [LnO8] Coordination Geometry in Lanthanide-Lithium β-Diketonates: Luminescence and Single-Ion Magnet Behavior

Functionalized perfluoroalkyl lithium β-diketonates (LiL) react with lanthanide(III) salts (Ln = Eu, Gd, Tb, Dy) in methanol to give heterobimetallic Ln-Li complexes of general formula [(LnL₃)(LiL)(MeOH)]. The length of fluoroalkyl substituent in ligand was found to affect the crystal packing of complexes. Photoluminescent and magnetic properties of heterobimetallic β-diketonates in the solid state are reported. The effect of the geometry of the [LnO₈] coordination environment of heterometallic β-diketonates on the luminescent properties (quantum yields, phosphorescence lifetimes for Eu, Tb, Dy complexes) and single-ion magnet behavior (U_eff for Dy complexes) is revealed.

5-Amino-2-aryl-2H-1,2,3-triazole-4-carboxamides: Unique AIEE-gens and selective Hg2+ fluorosensors

A series of fluorescent sensors based on small molecule were designed and fully characterised, demonstrating AIEE effect and revealing an outstanding ability to selectively detect Hg²⁺ ions. The structural and electronic properties were studied through quantum chemical calculations at (Time-Dependent) Density Functional Theory ((TD)-DFT) level. Carboxamides of 2-Aryl-1,2,3-Triazoles (CATs) showed significant differences in their photophysical properties depending on the structure of the substituent at amino function on the C5-atom in the heterocycle. When the tert-cycloalkylamino group (pyrrolidine, piperidine, azepane) was attached, the triazoles exhibited highly intensive blue fluorescence, with quantum yields (QYs) up to 95 % and lifetime up to 6.9 ns in different solvents, whereas the QYs of congeners bearing secondary alkylaminogroups (viz., NHMe, NHC₆H₁₁-cyclo) indicate low QYs (1-10 %). Nevertheless, all types of the obtained fluorophores demonstrated excellent AIEE effect and formed fluorescent nanoparticles in a binary mixtures of organic solvents and water. The introduction of the carboxamide function enhances the sensing properties of 2-aryl-1,2,3-triazoles, providing a selective fluorescence quenching reaction in the presence of Hg²⁺. The fluorescence intensity of the CATs declines with the addition of 1.0 eq. of Hg²⁺ into DMSO-water (v/v, 1:9). The other cations used did not induce any appreciable changes in fluorescence intensity. The CATs form a complex with Hg²⁺ with highly specific detection for Hg²⁺ over other competitive metal ions: the detection limits were determined to be 0.23 and 0.15 μM for the CATs 1b and 2c. The reverse effect was registered with the addition of ethylene diamine sodium salt; meanwhile, the CATs demonstrated more effective coordination with Hg²⁺ in comparison with cysteine. This last finding, as well as the ability to detect Hg²⁺, is very valuable for application within biology and medicine.

Mesomeric Betaines Based on Adamantylated 1,2,4-Triazolo[4,3-a]pyrimidin-5-ones: Synthesis, Structure and Conversion into Anionic N-Heterocyclic Carbenes

The C-N coupling of 1,2,4-triazolo[1,5-a]pyrimidin-7-ones with 1-adamantanol/1-bromoadamantane leads to 1,2,4-triazolo[4,3-a]pyrimidinium-5-olates, which are represented as mesomeric betaines (MBs). The formation of MBs involves not only N-alkylation of heterocyclic framework but also the rearrangement leading to a change in the type of fusion between pyrimidine and 1,2,4-triazole fragments. The structures of the obtained products were confirmed by the X-ray analysis and measurements of ¹³ C-¹³ C (J_CC ) coupling constants in the 1D ¹³ C NMR spectra of selectively ¹³ C-labeled samples. Treatment of the betaines with lithium bis(trimethylsilyl)amide (LiHMDS) gave anionic carbenes, which were detected by ¹³ C NMR spectroscopy and were trapped by reactions with phenyl isothiocyanate and sulfur. Density functional theory (DFT) and the quantum theory of atoms in molecules (QTAIM) analyses allowed for an insight into the electronic structure of the obtained betaines and N-heterocyclic carbene derivatives.

4-(Aryl)-Benzo[4,5]imidazo[1,2-a]pyrimidine-3-Carbonitrile-Based Fluorophores: Povarov Reaction-Based Synthesis, Photophysical Studies, and DFT Calculations

A series of novel 4-(aryl)-benzo[4,5]imidazo[1,2-a]pyrimidine-3-carbonitriles were obtained through the Povarov (aza-Diels-Alder) and oxidation reactions, starting from benzimidazole-2-arylimines. Based on the literature data and X-ray diffraction analysis, it was discovered that during the Povarov reaction, [1,3] sigmatropic rearrangement leading to dihydrobenzimidazo[1,2-a]pyrimidines took place. The structures of all the obtained compounds were confirmed based on the data from ¹H- and ¹³C-NMR spectroscopy, IR spectroscopy, and elemental analysis. For all the obtained compounds, their photophysical properties were studied. In all the cases, a positive emission solvatochromism with Stokes shifts from 120 to 180 nm was recorded. Aggregation-Induced Emission (AIE) has been illustrated for compound 6c using different water fractions (fw) in THF. The compounds 6c and 6f demonstrated changes in emission maxima or/and intensities after mechanical stimulation.

Copper(ii) complexes with terpene derivatives of ethylenediamine: synthesis, and antibacterial, antifungal and antioxidant activity

The synthesis of new chiral copper(ii) complexes with terpene derivatives of ethylenediamine and the results of studying their antibacterial, antifungal and antioxidant activity in vitro are discussed. All studied copper complexes (1–4) showed significantly higher antifungal activity against the strains of C. albicans, S. salmonicolor and P. notatum compared to the activity of the clinical antifungal drug amphotericin. High antibacterial activity of copper complexes with terpene derivatives of ethylenediamine was revealed against the S. aureus (MRSA) strain, which is resistant to the reference antibiotic ciprofloxacin. Using various test systems, a comparative assessment of the antioxidant activity (AOA) of the synthesized copper complexes and the ligands was carried out. The salen-type complex 4, which has the highest AOA in the model of initiated oxidation of a substrate containing animal lipids, was superior to other copper complexes in the ability to protect erythrocytes under conditions of H₂O₂-induced hemolysis.

The synthesis of new chiral copper(ii) complexes with terpene derivatives of ethylenediamine and the results of studying their antibacterial, antifungal and antioxidant activity in vitro are discussed.

Regiospecific way to N9-alkylated thioxanthines

A regiospecific way to N9-alkylated thioxanthines as novel acyclic nucleoside analogues has been developed. This approach is based on a cleavage methodology involving the construction of a target heterocyclic scaffold...

New heteroanalogs of tricyclic ascidian alkaloids: synthesis and biological activity

Heteroanalogs of ascidian alkaloids have been synthesized, and for the first time 10 different types of saturated carbo- and heteroannulated pyridones have been obtained. A new method for the formation of decahydro[1,3]oxazolo[2,3-j]quinoline and octahydro-5H-cyclopenta[b][1,3]oxazolo[3,2-a]pyridine was proposed. The synthesis of these heterocycles is based on the three-component cyclization of trifluoroacetoacetic ester and cycloketones with 1,2- and 1,3-dinucleophiles. It was found that reactions with amino alcohols are distinguished by the possibility of isolating carbocyclopyridones of various degrees of saturation. The diastereomeric structure of the synthesized heterocycles has been studied, and the mechanism of their formation has been proposed. Antitumor, anti-influenza and analgesic agents have been found among the synthesized compounds.

Photophysics, photochemistry and bioimaging application of 8-azapurine derivatives

New 2-aryl-1,2,3-triazolopyrimidines were designed, synthesized, and characterized. Their optical properties were thoroughly studied in the solid phase, in solution and in a biological environment. Density Functional Theory (DFT) based calculations were performed, including the molecular geometry optimization for both the ground state and the first singlet excited state, the prediction of the UV-Vis absorption and fluorescence spectra, the determination of the molecular electrostatic properties and the solvent effect on the optical properties. The emission intensity was revealed to increase in time upon irradiation. Mass spectrometric research, quantum mechanical calculations, and analysis of literature data suggested a possible photo-transformation pathway through the homolytic cleavage of one of the C-Cl bonds upon irradiation with UV light. The structure of the active intermediate was identified by the series of mass spectrometry experiments and via synthesis of putative transformation products. The kinetic parameters measured in different solvents allowed estimating the rate of these photo-transformations. Biological experiments demonstrated that 2-aryl-1,2,3-triazolopyrimidines penetrate cells and selectively accumulate in the cell membrane and the Golgi complex and endoplasmic reticulum. Their unique properties pave the way for new possible applications of fluorescent 8-azapurines in biology and medicine.

Electrochemical Aromatization of Dihydroazines: Effect of Chalco­genophosphoryl (CGP) Substituents on Anodic Oxidation of 9-CGP-9,10-dihydroacridine

The effect of chalcogenophosphoryl fragments on the anodic oxidation of 9-chalcogenophosphoryl-9,10-dihydroacridines was studied in detail. The data of X-ray structural analyses, quantum chemical calculations, and cyclic voltammetry measurements obtained for these compounds provide an explanation of the observed features. The direct electrochemical phosphorylation of acridine was first carried out successfully.

Methods of Synthesis and Antiviral Activity of New 4-Alkyl-3-Nitro-1,4-Dihydroazolo[5,1-c][1,2,4]Triazin-4-ols

An azo coupling reaction of α-nitro ketones with 5-diazoazoles was used to obtain 4-alkyl-3-nitro-1,4-dihydroazolo[5,1-с][1,2,4]triazines, which were characterized with respect to their antiviral activity against influenza and Coxsackie B3 viruses.

Design, synthesis, and photophysics of bi- and tricyclic fused pyrazolines

A three series of bi-cyclic and tri-cyclic functionalised pyrazoline fluorophores with high quantum yields and positive solvato(fluoro)chromism were designed and synthesised by improved method.

The Rh(iii)-catalysed C–H/N–H annulation of 2-thienyl- and 2-phenyl-quinazolin-4(3H)-ones with diphenylacetylene

2-Thienyl/phenyl substituted quinazolin-4(3H)-ones were converted into 4,5-diphenyl-7H-thieno[2′,3′:3,4]pyrido[2,1-b]quinazolin-7-ones or amide alcoholysis product via Rh(iii)-catalyzed reaction of with diphenylacetylene.

Two Approaches for the Synthesis of Fused Dihydropyridines via a 1,6-Electrocyclic Reaction: Fluorescent Properties and Prospects for Application

Reactions of penta-2,4-dienethioamides with acetylenedicarboxylic acid, methyl and ethyl esters, and methyl propiolate were systematically studied, and a number of new 2,3-dihydro-5H-thiazolo[3,2-a]pyridines (DTPs) and 4H,6H-pyrido[2,1-b][1,3]thiazines (PTZs) were prepared. A possible mechanism for a multistep domino transformation is suggested, and the key step is the 1,6-electrocyclic reaction. An additional alternative method for the synthesis of new heterocyclic systems was achieved. Evidence of the electrocyclic mechanism of a key step was collected from the analysis of the spatial structure of the synthesized bicyclic nonaromatic pyridines by X-ray diffraction and quantum chemical calculations, as well as from the thermodynamic quantities. DTPs exhibited yellow fluorescence in solution and yellow to red emissions in the solid state. Biological investigations demonstrated the ability of DTPs to penetrate living and fixed cells and presumably accumulate in lysosomes.

Rearrangement of 7-Aryloxazolo[5,4-b]pyridines to Benzo[c][1,7]naphthyridine-4(3H)-ones and Thieno[3,2-c][1,7]naphthyridine-6(7H)-ones

In this work, we describe the development of the rearrangement for 7-aryl-substituted oxazolo[5,4-b]pyridines treated with aluminum chloride into synthetically hard-to-reach benzo[c][1,7]naphthyridinones. The discovered rearrangement is applied to a variety of electron-rich (hetero)arene substrates. It offers the advantages of mild conditions (90 °C temperature), fast reaction rates (<4 h), compatibility with air moisture, and the use of inexpensive commercial reagents. The proposed reaction mechanism and key elementary reaction acts were studied in detail using quantum chemical calculations. The photophysical properties of the synthesized compounds were studied by steady-state UV-vis spectroscopy.

Competitive ways for three-component cyclization of polyfluoroalkyl-3-oxo esters, methyl ketones and amino alcohols

The competitive routes were found for three-component cyclization of polyfluoroalkyl-3-oxo esters, methyl ketones with 3-amino alcohols. It was shown that the reactions with 3-aminopropanol in 1,4-dioxane predominantly lead to hexahydropyrido[2,1-b][1,3]oxazin-6-ones, and in ethanol to 3-hydroxypropylaminocyclohexenones. In contrast, cyclizations with 2-aminoethanol and its analogues, regardless of the reaction conditions, yield hexahydrooxazolo[3,2-a]pyridin-5-ones as the main products. The trans- and cis-diastereomeric structure of heterocycles was established using X-ray and 1H, 19F, 13C NMR spectroscopy, 2D 1H-13C HSQC and HMBC experiments. The mechanism is proposed for competitive transformations of polyfluoroalkyl-3-oxo esters, methyl ketones with 3-amino alcohols.

Dibenzo[f,h]furazano[3,4-b]quinoxalines: Synthesis by Intramolecular Cyclization through Direct Transition Metal-Free C-H Functionalization and Electrochemical, Photophysical, and Charge Mobility Characterization

Herein, we describe the synthesis of unsymmetrically substituted dibenzo[f,h]furazano[3,4-b]quinoxalines by intramolecular cyclization through direct transition metal-free C-H functionalization. The electrochemical and photophysical properties for several polycycles have been measured. In thin films of the dibenzo[f,h]furazano[3,4-b]quinoxalines, hole mobility is in the order of 10^-4 cm² V^-1 s^-1. The results show that the HOMO and LUMO energy levels are appropriate for using the compounds as hole-transport materials in thin-film devices, in particular, organic and perovskite solar cells.

1-Nicotinoylbenzotriazole: A Convenient Tool for Site-Selective Protection of 5,7-Dihydroxycoumarins

1-Nicotinoylbenzotriazole (NicBt) was uncovered as an efficient protecting agent for the site-selective acylation of resorcinol-type phenolic groups with almost equal reactivity. The use of NicBt allows selective protection of the 7-OH group in 5,7-dihydroxycoumarins in one simple scalable step, while combination of the nicotinoylation with tosylation–denicotinoylation or silylation–denicotinoylation yields 5-OH-protected 5,7-dihydroxycoumarins. Furthermore, nicotinoylated 5,7-dihydroxycoumarins proved useful in a gram-scale three-step preparation of a 2,2-dimethylpyrano[2,3-f]coumarin, a key intermediate for the synthesis of calanolide A, an HIV reverse transcriptase and Mycobacterium tuberculosis inhibitor, and its active analogues.

Autocatalyzed three-component cyclization of polyfluoroalkyl-3-oxo esters, methyl ketones and alkyl amines: a novel approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones

A new one-pot reaction between polyfluoroalkylated 3-oxo esters, methyl ketones and primary or secondary alkyl amines is reported as an efficient approach to 3-alkylamino-5-hydroxy-5-polyfluoroalkylcyclohex-2-en-1-ones. The scope of three-component cyclization and its plausible mechanism are discussed. The described protocol makes it possible to vary the functional substituents in 2, 3 and 5 positions of carbocycles. Anhydrous conditions are necessary for the productive synthesis of aminocyclohexenones, whereas in the presence of water the competitive formation of alkyl ammonium salts of keto hydroxy carboxylates is observed. Dehydration of the aminocyclohexenones was effectively used for the synthesis of 3-alkylamino-5-trifluoromethylphenols, some of which exhibited moderate antifungal activities against eight pathogenic fungal strains.

Fluorescent boron complexes based on new N,O-chelates as promising candidates for flow cytometry

This study presents the synthesis and optical properties of a new class of bright green-yellow fluorescent dyes with potential applications in bioimaging. A facile synthetic route via the chelation of aryl(hetaryl)aminoacryloylthiophene scaffolds with a BF2 fragment is presented. The photophysical properties of the dyes are attributed to the nature and position of electron-donating and electron-withdrawing substituents. Upon coordination to a BF2 fragment, characteristic emission was observed, with λem ranging from 503 to 543 nm and quantum yields of 0.14-0.42. Compared with parent aryl(hetaryl)aminoacryloylthiophenes, a significant red shift in absorption (up to 480 nm in solution) and emission (up to 543 nm in solution and 610 nm in the solid state) and high chemical stability and photostability were observed. The electron-accepting character of the substituents on the terminal aromatic ring or replacing this fragment with pyridine or pyrazine moieties resulted in increased quantum yields. To gain insight into the electronic structures and optical properties, quantum mechanical calculations were performed. The results of (TD-)DFT calculations supported the structural and spectroscopic data and showed the features of electronic distribution in the frontier molecular orbitals and active electrophilic and nucleophilic sites in the compounds investigated. Synthesized BF2 complexes are promising dyes for cell imaging and flow cytometry owing to their ready penetration and accumulation in cells.