Recyclization of 5-Amino- oxazoles as a Route to new Functionalized Heterocycles (Developments of V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the NAS of Ukraine).

The recyclizations of 5-amino- and 5-hydrazine-1,3-oxazoles mainly with electron-withdrawing group in 4th position are considered. The chemical behavior of these heterocycles is due to the presence of two hidden amide fragments; therefore, the recyclization processes include a stage of nucleophile attack on 2nd or 5th position of the oxazole cycle. When the nitrile group is present in 4th position, it is often involved in the recyclization forming α-aminoazoles. 5-Amino/hydrazine-1,3-oxazoles undergo recyclization both in nucleophilic (amines, hydrazine, thionating agents) and electrophilic medium ((trifluoro)acetic acid, other acylating agents). The numerous types of functionalized heterocycles can be easily obtained with the usage of these recyclizations, such as the derivatives of 3-amino-6,7-dihydro-5H-pyrrolo[1,2-a]imidazole, imidazolidine-2,4-dione, 1H-pyrazole-3,4,5-triamine, 5,6-diamino-2,3-diphenylpyrimidin-4(3H)-one, 2-(2-R-7-oxo-5-(trifluoromethyl)oxazolo[5,4-d]pyrimidin-6(7H)-yl)acetic acid, 2-R-4-(5-R'-1,3,4-oxadiazol-2-yl)oxazol-5-amine, (amino(5-amino-1,3,4-thiadiazol-2-yl)methyl)phosphonate.

Rapid synthetic approaches to libraries of diversified 1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones and 3-(2-hydroxyphenyl)-4,5-dihydropyrrolo[3,4-c]pyrazol-6(1H)-ones.

An efficient and practical synthetic procedure for libraries of diversified 1,2-dihydrochromeno[2,3-c]pyrrole-3,9-diones using a multicomponent process is presented. A convenient synthetic procedure for obtaining functionalized 3-(2-hydroxyphenyl)-4,5-dihydropyrrolo[3,4-c]pyrazol-6(1H)-ones via ring-opening strategy has also been developed. This protocol was found to be compatible with a wide range of substituents and paves the way for the practical synthesis of title compounds with a broad range of substituents under mild condition. The products can be easily isolated by crystallization without the use of chromatography.

In silico and in vitro Estimation of Structure and Biological Affinity of 1,3- Oxazoles: Fragment-to-fragment Approach.

BACKGROUND: The fragment-to-fragment approach for the estimation of the biological affinity of the pharmacophores with biologically active molecules has been proposed. It is the next step in the elaboration of molecular docking and using the quantum-chemical methods for the complex modeling of pharmacophores with biomolecule fragments. METHODS: The parameter φ 0 was used to estimate the contribution of π-electron interactions in biological affinity. It is directly related to the position of the frontier levels and reflects the donor-acceptor properties of the pharmacophores and stabilization energy of the [Pharm꞉BioM] complex Results: By using quantum-chemical calculations, it was found that the stacking interaction of oxazoles with phenylalanine is 7-11 kcal/mol, while the energy of hydrogen bonding of oxazoles with the amino group of lysine is 5-9 kcal/mol. The fragment-to-fragment approach can be applied for the investigation of the dependence of biological affinity on the electronic structure of pharmacophores.c Conclusion: The founded quantum-chemical regularities are confirmed with the structure-activity relationships of substituted oxazoles.

Theoretical and Experimental Studies of Phosphonium Ionic Liquids as Potential Antibacterials of MDR Acinetobacter baumannii.

A previously developed model to predict antibacterial activity of ionic liquids against a resistant A. baumannii strain was used to assess activity of phosphonium ionic liquids. Their antioxidant potential was additionally evaluated with newly developed models, which were based on public data. The accuracy of the models was rigorously evaluated using cross-validation as well as test set prediction. Six alkyl triphenylphosphonium and alkyl tributylphosphonium bromides with the C8, C10, and C12 alkyl chain length were synthesized and tested in vitro. Experimental studies confirmed their activity against A. baumannii as well as showed pronounced antioxidant properties. These results suggest that phosphonium ionic liquids could be promising lead structures against A. baumannii.

Intrinsic drug potential of oxazolo[5,4-d]pyrimidines and oxazolo[4,5-d]pyrimidines.

The oxazole and pyrimidine rings are widely displayed in natural products and synthetic molecules. They are known as the prime skeletons for drug discovery. On the account of structural and chemical diversity, oxazole and pyrimidine-based molecules, as central scaffolds, not only provide different types of interactions with various receptors and enzymes, showing broad biological activities, but also occupy a core position in medicinal chemistry, showing their importance for development and discovery of newer potential therapeutic agents (Curr Top Med Chem, 16, 2016, 3133; Int J Pharm Pharm Sci, 8, 2016, 8; BMC Chem, 13, 2019, 44). For a long time, relatively little attention has been paid to their fused rings that are oxazolopyrimidines, whose chemical structure is similar to that of natural purines because probably none of these compounds were found in natural products or their biological activities turned out to be unexpressed (Bull Chem Soc Jpn, 43, 1970, 187). Recently, however, a significant number of studies have been published on the biological properties of oxazolo[5,4-d]pyrimidines, showing their significant activity as agonists and antagonists of signaling pathways involved in the regulation of the cell life cycle, whereas oxazolo[4,5-d]pyrimidines, on the contrary, represent a poorly studied class of compounds. Limited access to this scaffold has resulted in a corresponding lack of biological research (Eur J Organ Chem, 18, 2018, 2148). Actually, oxazolo[5,4-d]pyrimidine is a versatile scaffold used for the design of bioactive ligands against enzymes and receptors. This review focuses on biological targets and associated pathogenetic mechanisms, as well as pathological disorders that can be modified by well-known oxazolopyrimidines that have been proven to date. Many molecular details of these processes are omitted here, which the interested reader will find in the cited literature. This work also does not cover the methods for the synthesis of the oxazolopyrimidines, which are exhaustively described by De Coen et al. (Eur J Organ Chem, 18, 2018, 2148). The review as well does not discuss the structure-activity relationship, which is described in detail in the original works and deliberately, whenever possible, cites not primary sources, but mostly relevant review articles, so that the reader who wants to delve into a particular problem will immediately receive more complete information. It is expected that the information presented in this review will help readers better understand the purpose of the development of oxazolopyrimidines and the possibility of their development as drugs for the treatment of a wide range of diseases.

1,3-Oxazole derivatives of cytisine as potential inhibitors of glutathione reductase of Candida spp.: QSAR modeling, docking analysis and experimental study of new anti-Candida agents.

Natural products as well as their derivatives play a significant role in the discovery of new biologically active compounds in the different areas of our life especially in the field of medicine. The synthesis of compounds produced from natural products including cytisine is one approach for the wider use of natural substances in the development of new drugs. QSAR modeling was used to predict and select of biologically active cytisine-containing 1,3-oxazoles. The eleven most promising compounds were identified, synthesized and tested. The activity of the synthesized compounds was evaluated using the disc diffusion method against C. albicans M 885 (ATCC 10,231) strain and clinical fluconazole-resistant Candida krusei strain. Molecular docking of the most active compounds as potential inhibitors of the Candida spp. glutathione reductase was performed using the AutoDock Vina. The built classification models demonstrated good stability, robustness and predictive power. The eleven cytisine-containing 1,3-oxazoles were synthesized and their activity against Candida spp. was evaluated. Compounds 10, 11 as potential inhibitors of the Candida spp. glutathione reductase demonstrated the high activity against C. albicans M 885 (ATCC 10,231) strain and clinical fluconazole-resistant Candida krusei strain. The studied compounds 10, 11 present the interesting scaffold for further investigation as potential inhibitors of the Candida spp. glutathione reductase with the promising antifungal properties. The developed models are publicly available online at http://ochem.eu/article/120720 and could be used by scientists for design of new more effective drugs.

In silico and in vitro studies of a number PILs as new antibacterials against MDR clinical isolate Acinetobacter baumannii.

QSAR analysis of a set of previously synthesized phosphonium ionic liquids (PILs) tested against Gram-negative multidrug-resistant clinical isolate Acinetobacter baumannii was done using the Online Chemical Modeling Environment (OCHEM). To overcome the problem of overfitting due to descriptor selection, fivefold cross-validation with variable selection in each step of the model development was applied. The predictive ability of the classification models was tested by cross-validation, giving balanced accuracies (BA) of 76%-82%. The validation of the models using an external test set proved that the models can be used to predict the activity of newly designed compounds with a reasonable accuracy within the applicability domain (BA = 83%-89%). The models were applied to screen a virtual chemical library with expected activity of compounds against MDR Acinetobacter baumannii. The eighteen most promising compounds were identified, synthesized, and tested. Biological testing of compounds was performed using the disk diffusion method in Mueller-Hinton agar. All tested molecules demonstrated high anti-A. baumannii activity and different toxicity levels. The developed classification SAR models are freely available online at http://ochem.eu/article/113921 and could be used by scientists for design of new more effective antibiotics.

QSAR Study of Some 1,3-Oxazolylphosphonium Derivatives as New Potent Anti-Candida Agents and Their Toxicity Evaluation.

BACKGROUND: The incidence of invasive fungal infections caused by Candida spp. has increased continuously in recent decades, especially in populations of immunocompromised patients or individuals hospitalized with serious underlying diseases. Therefore, the goal of our study was the search for new potent Candida albicans inhibitors via the development of QSAR models that could speed up this search process. A number of the most promising 1,3-oxazol-4-yltriphenylphosphonium derivatives with predicted activities were synthesized and experimentally tested. Furthermore, the toxicity of the studied compounds was determined in vitro using acetylcholinesterase enzyme as a biological marker. METHODS: The classification QSAR models were created using Random Forests (WEKA-RF), k-Nearest Neighbors and Associative Neural Networks methods and different combinations of descriptors on the Online Chemical Modeling Environment (OCHEM) platform. Аntifungal properties of the investigated compounds were performed using standard disk diffusion method. The enzyme inhibitory action of the compounds was determined by modified Ellman's method using acetylcholinesterase from the electric organ of Electrophorus electricus. RESULTS: Three classification QSAR models were developed by the WEKA-RF, k-NN and ASNN methods using the ALogPS, E-State indices and Dragon v.7 descriptors. The predictive ability of the models was tested through cross-validation, giving a balanced accuracy BA = 80-91%. All compounds demonstrated good antifungal properties against Candida spp. and slight inhibition of the acetylcholinesterase activity. CONCLUSION: The high percentage of coincidence between the QSAR predictions and the experimental results confirmed the high predictive power of the developed QSAR models that can be applied as tools for finding new potential inhibitors against Candida spp. Furthermore, 1,3-oxazol-4- yl(triphenyl)phosphonium salts could be considered as promising candidates for the treatment of candidiasis and the disinfection of medical equipment.

In silico study of 4-phosphorylated derivatives of 1,3-oxazole as inhibitors of Candida albicans fructose-1,6-bisphosphate aldolase II.

In this study, the synthesis, in vitro anti-Candida activity and molecular modeling of 4-phosphorylated derivatives of 1,3-oxazole as inhibitors of Candida albicans fructose-1,6-bisphosphate aldolase (FBA-II) are demonstrated and discussed. Significant similarity of the primary and secondary structure, binding sites and active sites of FBA-II C. albicans and Mycobacterium tuberculosis are established. FBA-II C. albicans inhibitors contained 1,3-oxazole-4-phosphonates moiety are created by analogy to inhibitors FBA-II M. tuberculosis. The experimental studies of the anti-Candida activity of the designed and synthesized compounds have shown their high activity against standard strain and its C. albicans fluconazole resistant clinical isolate. It was hypothesized that the growth suppression of fluconazole-resistant С. albicans strain may be due to the inhibition of aldolase fructose-1,6-bisphosphate. A qualitative homology 3D model of the C. albicans FBA-II was created using SWISS-MODEL server. The probable mechanism of FBA-II inhibition by studied 4-phosphorylated derivatives was shown using molecular docking. The main role of amino acid residues His110, His226, Gly227, Leu248, Val238, Asp144, Lys230, Glu147, Gly227, Ala112, Leu145 and catalytic zinc atom in the formation of stable ligand-protein complexes with ΔG = -6.89, -7.2, -7.16, -7.5, -8.0, -7.9 kcal/mol was shown. Thus, the positive results obtained in the work were demonstrated the promise of using the proposed homology 3D model of the C. albicans FBA-II as the target for the search and development of new anti-Candida agents against azole-resistant fungal pathogens. Designed and studied 4-phosphorylated derivatives of 1,3-oxazole having a direct inhibiting FBA-II molecular mechanism of action can be used as perspective drug-candidates against resistant C. albicans strains.

One-Pot Parallel Synthesis of 5-(Dialkylamino)tetrazoles.

Two protocols for the combinatorial synthesis of 5-(dialkylamino)tetrazoles were developed. The best success rate (67%) was shown by the method that used primary and secondary amines, 2,2,2-trifluoroethylthiocarbamate, and sodium azide as the starting reagents. The key steps included the formation of unsymmetrical thiourea, subsequent alkylation with 1,3-propane sultone and cyclization with azide anion. A 559-member aminotetrazole library was synthesized by this approach; the overall readily accessible (REAL) chemical space covered by the method exceeded 7 million feasible compounds.

Design, synthesis and evaluation of novel sulfonamides as potential anticancer agents.

Based on modern literature data about biological activity of E7010 derivatives, a series of new sulfonamides as potential anticancer drugs were rationally designed by QSAR modeling methods Сlassification learning QSAR models to predict the tubulin polymerization inhibition activity of novel sulfonamides as potential anticancer agents were created using the Online Chemical Modeling Environment (OCHEM) and are freely available online on OCHEM server at https://ochem.eu/article/107790. A series of sulfonamides with predicted activity were synthesized and tested against 60 human cancer cell lines with growth inhibition percent values. The highest antiproliferative activity against leukemia (cell lines K-562 and MOLT-4), non-small cell lung cancer (cell line NCI-H522), colon cancer (cell lines NT29 and SW-620), melanoma (cell lines MALME-3M and UACC-257), ovarian cancer (cell lines IGROV1 and OVCAR-3), renal cancer (cell lines ACHN and UO-31), breast cancer (cell line T-47D) was found for compounds 4-9. According to the docking results the compounds 4-9 induce cytotoxicity by the disruption of the microtubule dynamics by inhibiting tubulin polymerization via effective binding into colchicine domain, similar the E7010.

(Chlorosulfonyl)benzenesulfonyl Fluorides-Versatile Building Blocks for Combinatorial Chemistry: Design, Synthesis and Evaluation of a Covalent Inhibitor Library.

Multigram synthesis of (chlorosulfonyl)benzenesulfonyl fluorides is described. Selective modification of these building blocks at the sulfonyl chloride function under parallel synthesis conditions is achieved. It is shown that the reaction scope includes the use of (hetero)aromatic and electron-poor aliphatic amines (e.g., amino nitriles). Utility of the method is demonstrated by preparation of the sulfonyl fluoride library for potential use as covalent fragments, which is demonstrated by a combination of in silico and in vitro screening against trypsin as a model enzyme. As a result, several inhibitors were identified with activity on par with that of the known inhibitor.

Facile One-Pot Parallel Synthesis of 3-Amino-1,2,4-triazoles.

A 1,2,4-triazole motif is present in numerous commercialized and investigational bioactive molecules. Despite its importance for medicinal chemistry, there is a lack of convenient combinatorial approaches toward this molecular core. Herein, we present a synthetic strategy suitable for the quick preparation of a library of structurally diverse 1,2,4-triazoles in a one-pot setting. The key steps include the formation of thioureas followed by S-alkylation using 1,3-propane sultone and consecutive ring closure leading to the desired 1,2,4-triazoles. Parallel synthesis yields thousands of 1,2,4-triazoles in a cost- and time-efficient manner from commercially available chemicals.