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The C–H functionalization strategy was first applied to the Cu-mediated radical arylation reactions of triazolotriazines with aromatic diazonium salts. A series of C(3)-modified triazolo[5,1- c ][1,2,4]triazines were obtained in yields of up to 80% under mild conditions. The radical nature of the reaction mechanism was established by the TEMPO radical trap experiments. The developed method is characterized by its versatile application opportunities, particularly it allows C(3)-arylated azoloazine-derived compounds of various architectures to be available. The elaborated synthetic strategy is of interest in the directed design of azaheterocyclic biomolecules with diverse pharmacological applications. [ABSTRACT FROM AUTHOR]

A synthetic approach to prepare boron-enriched π-conjugated photoactive molecular systems based on ortho-carborane using the Cu(I)-catalyzed Sonogashira-type coupling reaction has been developed. The obtained luminophores have been found to possess absorption in the range of 300 to 400 nm, emission of up to 700 nm, and photoluminescence quantum yields of up to 99% in non-polar solvents. TD-DFT calculations have demonstrated that the luminophores are characterized by phosphorescent emission behavior with a lifetime of about 7 μs. In addition, the rigidochromism for the synthesized compounds has been revealed; particularly, the transition electronic state and bathochromic shift have been elucidated in the emission spectra. The exhibited luminescent characteristics indicate that the elaborated vinylcarborane fluorophores could be considered as promising building blocks in the design of advanced photofunctional materials for molecular electronics. [ABSTRACT FROM AUTHOR]

A series of 2,4-disubstituted pyrrolo[2,1-f][1,2,4]triazines containing both aryl and thienyl substituents were synthesized by exploiting the 1,3-cycloaddition reaction of N(1)-ethyl-1,2,4-triazinium tetrafluoroborates with dimethyl acetylenedicarboxylate. The antiviral activity of the synthesized compounds against influenza virus strain A/Puerto Rico/8/34 (H1N1) was studied in experiments on Madin-Darby canine kidney (MDCK) cell culture. Among the pyrrolo[2,1-f][1,2,4]triazine derivatives, compounds with low toxicity and high antiviral activity were identified. Dimethyl 4-(4-methoxyphenyl)-7-methyl-2-p-tolylpyrrolo[2,1-f][1,2,4]triazine-5,6-dicarboxylate was found to demonstrate the best antiviral activity (IC50 4 µg/mL and selectivity index 188). Based on the results of in vitro tests and molecular docking studies performed, a plausible mechanism of action for these compounds was suggested to involve inhibition of neuraminidase. [ABSTRACT FROM AUTHOR]

A synthetic strategy based on reactions of cyclic imine oxides, namely 2H-imidazole 1-oxides, with thiophenols mediated by acetyl chloride was successfully applied as a convenient tool to obtain a series of novel azaheterocyclic molecules, including water-soluble hydrochloride forms. Optimized reaction conditions found herein for the nucleophilic substitution of hydrogen (SNH) in non-aromatic azaheterocyclic substrates via the "addition-elimination" (SNH AE) scheme enabled 15 arylthiolated 2H-imidazoles to be prepared in yields of up to 90%. The developed methodology discloses an original synthetic way to obtain numerous azaheterocyclic molecules, which are of interest in the field of medicinal chemistry and materials science. [ABSTRACT FROM AUTHOR]

A convenient multistep synthetic methodology to afford prospective push‐pull fluorophores based on the N(2)‐fluoroaryl‐1,2,3‐triazole scaffold as valuable functional blocks in the design of blue‐emitting organic materials is reported. The strategy includes five synthetic steps with yields of 60–99% at each stage. The obtained photoactive molecules, 2‐fluoroaryl‐5‐aryl‐4‐methyl‐1,2,3‐triazoles, were found to possess a blue‐violet emission in the range of λ=330–440 nm and the absolute quantum yield of >99% in solvents of different polarities. The electron transfer mechanistic features in the excited states for the developed N(2)‐fluoroaryl‐1,2,3‐triazoles compared to the 1,2,3‐triazoles‐1‐oxide analogues were also studied by using DFT and CIS calculations. [ABSTRACT FROM AUTHOR]

The strategy of the nucleophilic substitution of hydrogen (SNH) was first applied for the metal-free C-H/C-H coupling reactions of 4H-imidazole 3-oxides with indoles. As a result, a series of novel bifunctional azaheterocyclic derivatives were obtained in yields up to 95%. In silico experiments on the molecular docking were performed to evaluate the binding possibility of the synthesized small azaheterocyclic molecules to the selected biotargets (BACE1, BChE, CK1δ, AChE) associated with the pathogenesis of neurodegenerative diseases. To assess the cytotoxicity for the synthesized compounds, a series of in vitro experiments were also carried out on healthy human embryo kidney cells (HEK-293). The leading compound bearing both 5-phenyl-4H-imidazole and 1-methyl-1H-indole moieties was defined as the prospective molecule possessing the lowest cytotoxicity (IC50 > 300 µM on HEK-293) and the highest binding energy in the protein–ligand complex (AChE, −13.57 kcal/mol). The developed compounds could be of particular interest in medicinal chemistry, particularly in the targeted design of small-molecule candidates for the treatment of neurodegenerative disorders. [ABSTRACT FROM AUTHOR]

This review outlines the data of numerous studies relating to the broad-spectrum antiviral drug Triazavirin that was launched on the Russian pharmaceutical market in 2014 as an anti-influenza drug (the international non-patented name is Riamilovir). The range of antiviral activity of Triazavirin has been significantly expanded during recent years; in particular, it has been shown that Triazavirin exhibits activity against tick-borne encephalitis, Rift Valley fever, West Nile fever, and other infections of viral etiology. This drug has been approved for treatment of influenza and acute respiratory infections by the Russian Ministry of Health on the basis of comprehensive clinical trials involving over 450 patients. Triazavirin was found to be a highly effective and well-tolerated drug, allowing its over-the-counter sale. The recently published data on the use of Triazavirin in clinical practice for the treatment of patients with COVID-19 are discussed, with special attention paid to potential biological targets for this drug. [ABSTRACT FROM AUTHOR]

Antimetabolites of folic acid represent a large group of drugs and drug candidates, including those for cancer chemotherapy. In this current review, the most common methods and approaches are presented for the synthesis of therapeutically significant antimetabolites of folic acid, which are Methotrexate (MTX), Raltitrexed (Tomudex, ZD1694), Pralatrexate, Pemetrexed, TNP-351, and Lometrexol. In addition, the applications or uses of these folic acid antimetabolites are also discussed. [ABSTRACT FROM AUTHOR]

Calix[4]arenes are, probably, the mostly explored macrocycles in the supramolecular chemistry. By means of the synthetic modification/functionalization of the upper or lower rims, as well as meso‐positions, the "host‐guest" properties of these macrocycles can be modulated in order to accommodate the guest molecules of various sizes and nature for supramolecular and coordination chemistry, and to perform various functions for materials science and for biomedical applications. In this review, we wish to highlight the most prospective synthetic approaches for the direct C−H functionalization of calixarene core with various functional moieties. Depending on the nature of the functional moiety these calix[4]arenes can serve as drug carriers and nano‐containers for the recognition, encapsulation or storage of bioactive molecules and for many other applications. Current review article deals with the recent examples of C(H)‐functionalization of calix[4]arenes, as well as selected patterns of direct C(H)‐modification of some calix[6]arenes and calix[4]pyrroles. [ABSTRACT FROM AUTHOR]

Mono- and bis-2-thienyl-substituted 1,3,7-triazapyrenes have been synthesized for the first time via BF3-mediated C–H/C–Li coupling of 1,3,7-triazapyrene with 2-thienyllithium in 33 and 51% yields, respectively. The photophysical properties of these polycyclic azaaromatics have been studied, with emission in the range of 450–500 nm and fluorescence quantum yields of up to 99% in methanol solutions being revealed. The turn-off chemosensing properties of 2-thienyl-substituted 1,3,7-triazapyrenes for the selective detection of nitroaromatics have also been assessed; in particular, the quenching constants according to the Stern–Volmer model, the quenching sphere radius according to the Perrin model, the detection limit and the quenching efficiency have been determined. In particular, 6,8-bis-(thiopen-2-yl)-1,3,7-triazapyrene, characterized by 10 times the quenching constant and limit of detection (LOD) compared to the mono-substituted analog, can be considered as the most promising chemosensor for determining nitroaromatic compounds. DFT calculations confirm the presence of intramolecular charge transfer (ICT) effects in the case of the obtained fluorophores and clarify the quenching mechanism for nitroaromatics. [ABSTRACT FROM AUTHOR]

Azapyrenes are the nitrogen isosteres of pyrene. Based on theoretical and experimental studies, electron–acceptor azapyrene domains may be considered as convenient scaffolds for constructing a large variety of "push–pull" π-conjugated chromophores with pronounced ICT properties. Over the past decade, due to the unrelenting interest in functional materials and modern methodologies such as cross-coupling, peri-annulation, direct C–H-functionalization, etc., methods for the synthesis of aryl(alkyl) K-functionalized azapyrenes and other derivatives have been developed, and their photophysical and electrochemical properties have been studied. This short review aims at critical analysis of the best known/modern methods for the preparation of functionalized azapyrene derivatives, as well as an assessment of their photophysical/electrochemical properties in comparison with the structural and electronic properties of the parent pyrene. [ABSTRACT FROM AUTHOR]

A convenient method for the synthesis of new highly in non-polar solvents soluble photoactive pentafluorophenyl-substituted and extended alkoxyphenyl-substituted 2,2′-bipyridines is reported. The synthetic strategy for the preparation of such ligands involves a sequence of several structural transformations, such as O-alkylation, nucleophilic substitution of hydrogen (SNH) in 1,2,4-triazine precursors via the 'addition–elimination' scheme, and the subsequent conversion of the obtained 1,2,4-triazines into 2,2′-bipyridines by means of the aza-Diels–Alder reaction. The photophysical properties of the synthesized novel pentafluoroaryl-substituted 2,2′-bipyridines were comprehensively studied. The obtained photophysical data indicate the competitive advantages of the herein reported pentafluoroarylated push–pull fluorophores, bearing extended aliphatic moieties, over their analogues containing benzoxy or phenolic fragments in terms of improvement in quantum yield and well-pronounced positive solvatochromism confirmed by the mathematical analysis according to the Lippert–Mataga equation. [ABSTRACT FROM AUTHOR]

An original approach to achieve the C(sp2)–H azolation of cyclic aldonitrones mediated by Selectfluor® has first been employed. By exploiting a metal-free, visible-light-promoted cross-dehydrogenative C–N coupling reaction between model aldonitrones, 2H-imidazole 1-oxides, and NH-containing azoles, a series of novel azaheterocyclic derivatives have been obtained in yields up to 94%. The elaborated protocol has proved to be appropriate for gram-scale processes and displayed potential for utilization in the synthesis of novel structural analogues of lanabecestat. Besides, mechanistic studies have revealed that this coupling reaction is likely to proceed via a nitroxide-involving radical pathway, encompassing a chain of electron transfer events, such as hydrogen atom transfer (HAT) and single electron transfer (SET). [ABSTRACT FROM AUTHOR]

Azoloazine derivatives are known as promising small molecules that are potentially able to counteract a broad spectrum of RNA viruses including SARS‐CoV‐2. However, a pool of synthetic pathways to provide convenient structural modification of such compounds without de novo construction of the heterocyclic scaffold is rather limited so far. This work proposes an approach to the direct C(sp2)−H functionalization of azolopyrimidine substrates with aromatic thiol residues, mediated by the iodine/persulfate reagent system. The reported herein sulfenylation protocol has afforded a series of previously undescribed azolopyrimidine‐based thioethers obtained in yields of up to 87 %. Applicability of the approach to the selenium‐centered synthons has been demonstrated as well. Besides, the in silico study with regard to the achieved cross‐coupling products has suggested the possible affinity to the SARS‐CoV‐2 main protease (Mpro), as follows from the conducted pharmacophore search and the molecular docking experiments. As a result, the developed synthetic transformation is expected to be of utility in the design of novel antiviral agents based on small azaheterocyclic molecules. [ABSTRACT FROM AUTHOR]

The [S.sub.N.sup.H] approach has given new possibilities in the synthesis of hetaryl-substituted nitronyl nitroxides. The characterizations of all persistent radicals obtained by [S.sub.N.sup.H] synthetic strategy have included X-ray crystal structures, EPR investigation and static magnetic susceptibility measurements.

Azaheterocyclic derivatives of 1,2-dicarba- closo -dodeca-borane (ortho -carborane) are known to be of particular interest due to numerous plausible applications, particularly, in medicine, materials science, and advanced technologies. Three principal synthetic strategies resulting in azaheterocyclic carboranes, in which boron-enriched and azaheterocyclic fragments are linked to each other, either directly by means of the C–C bonds or through a short spacer (CH2 , CH2 S, CH2 O, etc.), have been outlined. These synthetic approaches are of general character and can be used both individually and in combination to afford promising organoboron clusters of diverse architectures. 1 Introduction 2 C–C Cross-Coupling Strategies in the Synthesis of Azahetero-cyclic Carboranes 3 Carboryne-Based Transformation Strategies 4 Condensation Strategies: Reactions of Decaborane B10 H14 with Substituted Acetylenes 5 Conclusion and Outlook [ABSTRACT FROM AUTHOR]

Two novel synthetic approaches to realize the direct C(sp²)--H bond functionalization in cyclic nitrones are reported. Palladium(II)-catalyzed oxidative C--C coupling of 2,2-dialkyl-4-phenyl-2H-imidazole 1-oxides with indoles was shown to result in the formation of 5-indolyl-3-yl derivatives, while nucleophilic substitution of hydrogen (SNH) at C(5) of the same imidazole system was found to afford the corresponding deoxygenated compounds. [ABSTRACT FROM AUTHOR]

A non-catalytic C-C coupling of ferrocenyllithium and heterocyclic N-oxides 2 was carried out for the first time using the reaction of nucleophilic substitution of hydrogen (SNH) in azines. [ABSTRACT FROM AUTHOR]

The synthesis of inhibitors for oxidative stress-associated destructive processes based on 2H-imidazole-derived phenolic compounds affording the bifunctional 2H-imidazole-derived phenolic compounds in good-to-excellent yields was reported. In particular, a series of bifunctional organic molecules of the 5-aryl-2H-imidazole family of various architectures bearing both electron-donating and electron-withdrawing substituents in the aryl fragment along with the different arrangements of the hydroxy groups in the polyphenol moiety, namely derivatives of phloroglucinol, pyrogallol, hydroxyquinol, including previously unknown water-soluble molecules, were studied. The structural and antioxidant properties of these bifunctional 5-aryl-2H-imidazoles were comprehensively studied. The redox transformations of the synthesized compounds were carried out. The integrated approach based on single and mixed mechanisms of antioxidant action, namely the AOC, ARC, Folin, and DPPH assays, were applied to estimate antioxidant activities. The relationship "structure-antioxidant properties" was established for each of the antioxidant action mechanisms. The conjugation effect was shown to result in a decrease in the mobility of the hydrogen atom, thus complicating the process of electron transfer in nearly all cases. On the contrary, the conjugation in imidazolyl substituted phloroglucinols was found to enhance their activity through the hydrogen transfer mechanism. Imidazole-derived polyphenolic compounds bearing the most electron-withdrawing functionality, namely the nitro group, were established to possess the higher values for both antioxidant and antiradical capacities. It was demonstrated that in the case of phloroglucinol derivatives, the conjugation effect resulted in a significant increase in the antiradical capacity (ARC) for a whole family of the considered 2H-imidazole-derived phenolic compounds in comparison with the corresponding unsubstituted phenols. Particularly, conjugation of the polyphenolic subunit with 2,2-dimethyl-5-(4-nitrophenyl)-2H-imidazol-4-yl fragment was shown to increase ARC from 2.26 to 5.16 (104 mol-eq/L). This means that the considered family of compounds is capable of exhibiting an antioxidant activity via transferring a hydrogen atom, exceeding the activity of known natural polyphenolic compounds. [ABSTRACT FROM AUTHOR]

Pd(OAc)2/ Cu(OAc)2-mediated reaction of imidazole oxides with indoles provides a new approach to indolylimidazole oxides (III). [ABSTRACT FROM AUTHOR]

It is shown that SNH approach opens new possibilities in the synthesis of polyfunctional nitronyl and imino nitroxides. It is found that the interaction of 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl lithium salt Li1 with 3,6-diaryl-1,2,4-triazines leads to formation of the corresponding triazines bearing nitronyl nitroxide or imino nitroxide substituent at position 5 of the heterocycle. The reaction of Li1 with pyridazine-N-oxide gives rise to nitroxide with buten-3-ynyl substituent 5. Spin-labeled 5 could be readily transformed by the use of 1,3-dipolar and nucleophilic addition reactions, as well as oxidative coupling, that gives a large group of new paramagnets: 2-(1H-pyrazol-5-yl)vinyl-, 2-ethynylcyclopropyl-, 2-(3-(ethoxycarbonyl) isoxazol-5-yl)vinyl-, 1-(pyrrolidin-1-yl)but-3-ynyl-substituted nitronyl nitroxide and a diradical - 2,2'-((1E,7E)-octa-1,7-dien-3,5-diyne-1,8-diyl)bis(4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-3-oxide-1-oxyl). The new nitroxides were characterized by X-ray single crystal data, ESR and static magnetic susceptibility measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • A 1,3/1,4-diazine's modified SPE for NB determination in honey was prepared. • Cathodic currents of NB reduction enhanced the diazine-modified SPEs. • The best NB response was obtained by using co-polymerization of the receptor layer. • The low detection limit 0.107 μM allows NB in honey samples to be detected. • The analysis of spiked probes showed the high precision of the sensor with HPLC. In this work, a screen-printed electrode (SPE) modified by 1,3/1,4-diazines was prepared for the rapid and sensitive determination of nitrobenzene (NB). The obtained results indicated enhanced cathodic currents of direct NB reduction into hydroxylaminophenol on the diazine-modified SPEs. The enhanced effect was most likely due to the combination of complexation and collisional processes of diazines towards nitroaromatic compounds and also the diazine-modified electrodes' increased electroconductivity. The best electrochemical responses were obtained in square wave voltammetry mode by using the carbazolyl substituted diazines as a component of the sensitive layer, which was assembled by co-electropolymerization with the unsubstituted carbazole on the electrode during 5 cycles. The low detection limit estimated as 0.107 μM and wide linear range (1–1000 µM) enables NB in water and food samples to be determined. The developed modified electrode was applied in the analysis of commercial honey samples. [ABSTRACT FROM AUTHOR]

The methodology of nucleophilic substitution of hydrogen (S N H ) was successfully applied as a convenient synthetic tool to afford azaheterocyclic derivatives of phenols of various architectures. A series of 26 novel imidazole-linked polyphenolic compounds were first prepared in 72-95% yields through the direct metal-free C-H/C-H coupling of polyphenols with 2 H -imidazole 1-oxides. Comprehensive studies on the reaction condition optimization, scope, and limitations enabled the development of a straightforward method toward novel bifunctional derivatives bearing both phenolic and imidazole scaffolds of particular interest in the design of challenging molecules for versatile applications in medicinal chemistry and materials science.

A meso -functionalization strategy has successfully been applied to the synthesis of novel 1,3,7-triazapyrene derivatives of calixarenes. The key synthetic step in these transformations providing the direct C-C bond formation is nucleophilic substitution of hydrogen (S N H ) in 1,3,7-triazapyrene. General photophysical characteristics for these macrocyclic compounds, as well as features in emission properties upon addition of various metal cations have been elaborated. Studies using NMR spectroscopy have also shown a mutual effect of both calix[4]arene and 1,3,7-triazapyrene moieties on the coordination process. The complex stoichiometry and binding constants for Al 3+ and Fe 3+ guests have been explored with titration experiments., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Direct C(sp2)-H functionalization of the endocyclic azomethine and aldonitrone moieties in non-aromatic azaheterocycles has established itself as a promising methodology over the last decade. Transition metal-catalyzed cross-coupling reactions, α-metalation-electrophile quenching protocols, and (metal-free) nucleophilic substitution of hydrogen reactions (SNH) are the major routes applied on cyclic imines and their derivatives. In this overview, we show the tangible progress made in this area during the period from 2008 to 2020.

Methodology of nucleophilic substitution of hydrogen (S N H ) was first applied for the direct modification of nonaromatic 2 H -imidazoles to afford novel polyfluoroarylated azaheterocycles. Scope, tolerance for these transition-metal-free C-H/C-Li coupling reactions, and photophysical properties for the novel 4-(perfluorophenyl)-5-aryl-2 H -imidazoles were comprehensively studied. In particular, some of the obtained perfluoroaryl-substituted 2 H -imidazoles were found to be of particular interest as promising push-pull fluorophore systems in the design of fluorometric sensor materials due to the effect of intramolecular charge transfer.

The reaction of 6-chloro-1-methylpyrazin-2(1 H)-one with Grignard reactants followed by quenching with different electrophiles gave access to a variety of 3,6-difunctionalized 1-methylpyrazin-2(1 H)-ones. This regioselective three-component reaction represents the first example of a tele-nucleophilic substitution of hydrogen (S N H ) in which the anionic σ H adduct is quenched by electrophiles (other than a proton) before elimination takes place. Quenching the reaction with iodine (I 2 ) or bromine (Br 2 ) provides an alternative reaction pathway, yielding a 3-functionalized 6-chloro-1-methylpyrazin-2(1 H)-one or 5-bromo-6-chloro-1-methylpyrazin-2(1 H)-one, respectively. The halogens present offer opportunities for further selective transformations.