Project objectives

1) Investigation of N-arylation reactions of amidine-like systems using azine N-oxides, including those incorporating natural triterpenoid scaffolds-fragments of glycyrrhetinic and glycyrrhizic acids. Screening of reaction conditions and selection of the base and activating reagent to ensure optimal yield and process selectivity

2) Investigation of conjugation reactions of natural triterpenoid acids with privileged 2H-imidazoline fragments, as well as with 5-, 6-, and 7-membered amidine cycles. Conducting cyclocondensation reactions of amidine-containing amidoximes with triterpenoid acid derivatives under superbasic activation conditions, as well as using peptide synthesis methods

3) Expansion of the accessible range of azine N-oxides through oxidation reactions of azines, as well as reductive cyclization reactions of nitroaromatic derivatives

4) Development of synthetic methods for 2H-imidazoline and 5–7-membered cyclic amidine systems based on cyclodehydration reactions under the action of polyalkyl phosphate reagents. Selection of conditions for the synthesis of acyl derivatives of aliphatic diamines (ethylenediamine, propylenediamine, and their homologues). Identification of optimal temperatures and reagent ratios for the preparation of cyclic amidines from the obtained acyl derivatives of diamines using ethyl polyphosphate and its analogues

5) Investigation of the antimicrobial and antiviral activity of the obtained compounds in vitro. The antibacterial activity of the new compounds will be evaluated against a panel of Gram-positive and Gram-negative microbial strains (the ESKAPE pathogen group), including strains resistant to clinically used antibiotics, using the double serial dilution method with determination of the minimum inhibitory concentration (MIC). Primary antiviral activity assays will be conducted on Coxsackie virus strains in Vero cell culture using standard approaches (MTT assay, capsid thermostability, etc.)

6) Establishment of structure–activity relationships (SAR) and medicinal chemistry optimization of 2–3 lead compounds to generate drug candidates for the treatment of infectious diseases. Analysis of the biological activity of the obtained compound sets, optimization of solubility profiles, and structural optimization of hit compounds to improve bioavailability, along with the calculation of ADME parameters

Expected results

2024

As a result of the first year of the project, cyclodehydration reactions under the action of polyalkyl phosphate reagents leading to the formation of imidazoline and 5-, 6-, and 7-membered cyclic amidine-like systems will be investigated. The conditions of the cyclodehydration reaction will be optimized, and optimal reagents for the process will be proposed. Based on the developed approaches, imidazoline and 5-, 6-, and 7-membered cyclic amidine-like precursors will be synthesized for N-arylation reactions and conjugation with natural triterpenoid acids.

To study N-arylation reactions of amidine-like systems, synthetic strategies for the preparation of new aromatic azine N-oxides via reductive cyclization of nitroaromatic precursors will be developed. The scope of applicability of these approaches will be examined, and the reaction conditions will be optimized. A series of azine N-oxides will be synthesized for further investigation of N-arylation reactions.

The products of interaction between imidazoline and 5-, 6-, and 7-membered amidine cycles with azine N-oxides will be established. Data on the influence of the structure of amidine-like systems and azine N-oxides on the reaction parameters will be obtained. The effect of reaction conditions on product yields and process selectivity will be determined. As a result of the studies, series of N-arylated amidine systems will be synthesized, the structures of which will enable their conjugation with natural triterpenoid acids. The antibacterial activity of the obtained compounds will be investigated.

2025

As a result of the second year of the project, approaches to the conjugation of triterpenoid acids with amidine systems using linker structural fragments, represented by various five-membered heterocycles (1,2,4-oxadiazoles and other azoles) and amides, will be developed. Based on the developed methodologies, series of conjugates containing cyclic amidine-like systems, as well as their arylated derivatives, will be synthesized. In addition, the scope of applicability of the N-arylation strategy using azine N-oxides for cyclic amidine fragments already incorporated into conjugates with glycyrrhetinic and glycyrrhizic acids will be investigated.

Methods for determining antiviral and antibacterial activity will be verified and, if necessary, modified, and the activity of the synthesized compounds will be studied.

2026

As a result of the third year of the project, the antibacterial and antiviral properties of all synthesized compounds will be systematized. Based on the obtained data, structure–activity relationships (SAR) will be established, and a strategy for the structural optimization of lead compounds will be proposed.

Based on the developed synthetic approaches for the preparation of cyclic amidine systems, azine N-oxides, and conjugates of synthetic precursors with natural triterpenoid scaffolds, series of compounds optimized according to the established structure–activity relationships will be obtained. Through in vitro studies, optimized lead compounds will be identified for further extended in vivo investigations.

Results

New approaches to the synthesis of 2H-imidazoline and 5-, 6-, and 7-membered cyclic amidine systems have been developed.

In particular, a method for the synthesis of 1,2,4-oxadiazin-5(6H)-ones via the reaction of amidoximes with alkyl 2-halocarboxylates has been developed. As a result of the conducted studies, the optimal reaction conditions were determined: sodium tert-butoxide (2 equivalents) as the base, dimethyl sulfoxide as the solvent, and a reaction time of 18 h.

The conditions of the cyclodehydration reaction were optimized, and optimal reagents for the process were proposed.

2H-Imidazoline and other cyclic amidine precursors were synthesized for further studies.

The reliability of the obtained results is confirmed by the use of modern physicochemical methods: mass spectrometry (ESI), IR spectroscopy, ¹H and ¹³C NMR spectroscopy, and elemental analysis.

New aromatic azine N-oxides were synthesized via reductive cyclization of nitroaromatic precursors.

The scope and limitations of the reductive cyclization reaction for the synthesis of azine N-oxides were investigated.

A series of azine N-oxides was synthesized for further study of N-arylation processes.

For the synthesis of azine N-oxides via direct oxidation of the initial azaheterocycles, two methods were employed. First, hydrolytically and thermally stable compounds were obtained by heating the starting azaheterocycles in a mixture of acetic acid and 30% aqueous hydrogen peroxide at 80 °C for 16–20 hours. For the synthesis of more labile compounds, a system based on m-chloroperbenzoic acid in methylene chloride was used, with the reaction carried out at room temperature.

In addition, for the selective oxidation of bipyridine to the mono N-oxide, a mixture of 30% aqueous hydrogen peroxide and trifluoroacetic acid was used, with the reaction conducted at room temperature.

The products of interaction between imidazoline and other amidine cycles with azine N-oxides were investigated.

Data were obtained on the influence of the structure of amidine systems and azine N-oxides on the reaction parameters.

The effect of reaction conditions on product yields and process selectivity was studied.

Series of N-arylated imidazoline and amidine systems were synthesized, the structures of which enable their conjugation with natural triterpenoid acids.

During the study, it was established that imidazolines undergo arylation with pyridine N-oxides, forming mono- and diarylation products depending on the amount of pyridine N-oxide used. Successful reaction performance requires the use of a specific electrophilic activator. The best results were achieved using bromotripyrrolidinophosphonium hexafluorophosphate (PyBrOP); however, tosyl chloride (TsCl) can also be employed, although in this case the yields of the target products are lower. The reaction was carried out at room temperature in methylene chloride, using diisopropylethylamine as the base.

In addition, it was shown that, upon activation with PyBrOP, pyridine N-oxides are capable of reacting with amidoximes to form exclusively O-substitution products, namely O-pyridylamidoximes. The synthesis was performed in acetonitrile at room temperature, using diisopropylethylamine as the base.

Based on the results of the conducted studies, one article has been published in a journal indexed in the Science Citation Index Expanded, classified as Q2 by impact factor in the Web of Science database, and having an 83rd percentile CiteScore in the Scopus database.

Sofia I. Presnukhina, Valentina D. Kotlyarova, Anton A. Shetnev, Sergey V. Baykov, Rakhymzhan Turmanov, Nurbol Appazov, Rakhmetulla Zhapparbergenov, Leilya Zhussupova, Nurila Togyzbayeva, Stephanus J. Cloete, Mikhail K. Korsakov, Vadim P. Boyarskiy, Anél Petzer, Jacobus P. Petzer / Synthesis of 1, 2, 4-Oxadiazin-5 (6 H)-One Derivatives and Their Biological Investigation as Monoamine Oxidase Inhibitors // Molecules, 2024. Vol. 29(23), 5550. https://doi.org/10.3390/molecules29235550  

https://www.mdpi.com/1420-3049/29/23/5550