Stable σh-adducts in the reactions of the acridinium cation with heterocyclic N-nucleophiles

A reaction of NH-heterocycles with the 10-methylacridinium cation in the presence of a base led to 9,10-dihydro-10-methyl-9-substituted acridines, which can be considered as stable intermediates in the aromatic nucleophilic substitution reaction of hydrogen. The structure of the intermediates was studied and their oxidation potentials were determined. Generally, the oxidation potential was found to symbatically change with the changes in the energy of HOMO. © 2013 Springer Science+Business Media New York

Oxidizing agents in metal-catalyzed and metal-free C-H functionalization of heteroarenes

Oxidative C-H functionalization represents a crucial method to make new C-C, C-X (X = heteroatom) bonds. An optimal selection of the oxidizing agent goes hand in hand with the insight into the reaction mechanism. This review covers recent advances in methods of direct oxidative C-H functionalization of azines and their derivatives with heteroaromatic nucleophiles. Also we review the data on application of inorganic and organic oxidants for implementation of these reactions. C-H functionalizations under electrochemical and photocatalytic oxidation conditions are included as well. © AUTHOR(S)Russian Foundation for Basic Research, РФФИ: 19-29-08037, 20-43-660054We are grateful to the support from the Russian Foundation for Basic Research (Grants No. 20-43-660054 and 19-29-08037)

Synthesis, photophysical and redox properties of the 2,5,7-tri(het)aryl- [1,2,4]triazolo[1,5-a]pyrimidines

A number of Y-type push-pull compounds based on the [1,2,4]triazolo[1,5-a]pyrimidine core, namely 5,7- di(het)aryl-substituted 2-phenyl-[1,2,4]triazolo[1,5-a]pyrimidines, were obtained by transition metal free nucleophilic C-H functionalization. Substituents at both the C-5 and C-7 positions were introduced by successive treatment of the starting 6-bromo-2-phenyl-[1,2,4]triazolo[1,5-a]pyrimidine with Grignard reagents. In addition, the optical and electrochemical properties of the synthesized push-pull systems were studied. © 2020 Arkat. All rights reserved.This research study was supported financially by the Russian Science Foundation (Project No. 19-13-00234)

Oxidative Aromatization of 4,7-dihydro-6-nitroazolo[1,5-a] Pyrimidines: Synthetic Possibilities and Limitations, Mechanism of Destruction, and the Theoretical and Experimental Substantiation

The reaction tolerance of the multicomponent process between 3-aminoazoles, 1-morpholino2-nitroalkenes, and aldehydes was studied. The main patterns of this reaction have been established. Conditions for the oxidation of 4,7-dihydro-6-nitroazolo[1,5-a]pyrimidines were selected. Previous claims that the 4,7-dihydro-6-nitroazolo[1,5-a]pyrimidines could not be aromatised have now been refuted. Compounds with an electron-donor substituent at position seven undergo decomposition during oxidation. The phenomenon was explained based on experimental data, electro-chemical experiment, and quantum-chemical calculation. The mechanism of oxidative degradation has been proposed. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: The synthetic part was supported by the Ministry of Science and Higher Education of the Russian Federation, State Contract no FEUZ-2020-0058 (H687.42B.223/20). The electrochemical research and the quantum chemical calculations was funded by Russian Foundation for Basic Research (RFBR), project number 20-03-00814

Oxidative C-H/C-H Coupling of Dipyrromethanes with Azines by tio2-Based Photocatalytic System. Synthesis of New Bodipy Dyes and Their Photophysical and Electrochemical Properties

Oxidative C-H/C-H coupling reactions of dipyrromethanes with azines in the presence of a heterophase oxidative photocatalytic system (O2/TiO2/visible light irradiation) were carried out. As a result of cyclization of obtained compounds with boron trifluoride etherate, new hetaryl-containing derivatives of 4,4-difluoro-4-boron-3a,4a-diaza-s-indacene were synthesized. For the obtained compounds, absorption and luminescence spectra, quantum yields of luminescence as well as cyclic volt-amperograms were measured. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was supported by the Russian Foundation for Basic Research, research project numbers 20-43-660054 and 19-29-08037. The photophysical studies were carried out within the state assignment no AAAA-A19-119070790003-7

Derivatives of 9-phosphorylated acridine as butyrylcholinesterase inhibitors with antioxidant activity and the ability to inhibit β-amyloid self-aggregation: potential therapeutic agents for Alzheimer’s disease

We investigated the inhibitory activities of novel 9-phosphoryl-9,10-dihydroacridines and 9-phosphorylacridines against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and carboxylesterase (CES). We also studied the abilities of the new compounds to interfere with the self-aggregation of β-amyloid (Aβ42) in the thioflavin test as well as their antioxidant activities in the ABTS and FRAP assays. We used molecular docking, molecular dynamics simulations, and quantum-chemical calculations to explain experimental results. All new compounds weakly inhibited AChE and off-target CES. Dihydroacridines with aryl substituents in the phosphoryl moiety inhibited BChE; the most active were the dibenzyloxy derivative 1d and its diphenethyl bioisostere 1e (IC50 = 2.90 ± 0.23 µM and 3.22 ± 0.25 µM, respectively). Only one acridine, 2d, an analog of dihydroacridine, 1d, was an effective BChE inhibitor (IC50 = 6.90 ± 0.55 μM), consistent with docking results. Dihydroacridines inhibited Aβ42 self-aggregation; 1d and 1e were the most active (58.9% ± 4.7% and 46.9% ± 4.2%, respectively). All dihydroacridines 1 demonstrated high ABTS•+-scavenging and iron-reducing activities comparable to Trolox, but acridines 2 were almost inactive. Observed features were well explained by quantum-chemical calculations. ADMET parameters calculated for all compounds predicted favorable intestinal absorption, good blood–brain barrier permeability, and low cardiac toxicity. Overall, the best results were obtained for two dihydroacridine derivatives 1d and 1e with dibenzyloxy and diphenethyl substituents in the phosphoryl moiety. These compounds displayed high inhibition of BChE activity and Aβ42 self-aggregation, high antioxidant activity, and favorable predicted ADMET profiles. Therefore, we consider 1d and 1e as lead compounds for further in-depth studies as potential anti-AD preparations

Novel Oxidative Ugi Reaction for the Synthesis of Highly Active, Visible-Light, Imide-Acridinium Organophotocatalysts

A newly designed class of acridinium-based organophotocatalysts bearing an imide group at the C9-position is presented. To achieve these unprecedented structures, a synthetic strategy based on a novel straightforward oxidative Ugi-type reaction at the benzylic position of C9-unsubstituted acridanes was developed. The introduction of the imide-unit affords a notable photocatalytic activity enhancement, allowing efficient transformations in different oxidative and reductive visible-light catalytic reactions