Development of an effective and safe antioxidant compound is still challenging in the last few decades. There has been an increasing interest in the role of reactive oxygen species (ROS) in food, drugs, and even living system. Free radical formation is associated with the normal natural metabolism of aerobic cells. They are inevitably exposed to reactive oxygen species formed as oxygen metabolites. Oxidative stress which is largely characterized by reactive oxygen and nitrogen species is implicated in the development of a number of chronic and degenerative diseases such as atherosclerosis, cancer, cirrhosis, diabetes, wound healing and aging. Free radicals are highly reactive and therefore can attack membrane lipids, generating carbon radicals and peroxy radicals, which cause lipid peroxidation. Therefore, scientists in various disciplines have become more interested in naturally-occurring antioxidants as well as in related synthetic derivatives that could provide active components which prevent or reduce the impact of oxidative stress. Іn order to study the effect of various substituents in the molecules on the nature of thepharmacological activity of thiazolo[4,5-b]pyridin-2-ones, a series of new compounds were synthesized based on the previously obtained 5,7-dimethyl-3Hthiazolo[4,5-b]pyridin-2-one. The high electrophilicity of the N3 position in 5,7-dimethyl-3H-thiazolo[4,5-b]pyridin- 2-one allows to use of its functionalization as a convenient method for obtaining various N3-substituted derivatives to expand the range of thiazolo[4,5-b]pyridines. In particular, an NH center with a mobile hydrogen atom at the N3 position in 5,7-dimethyl-3H-thiazolo[4,5-b]pyridin-2-one allows conducting a synthesis based on 3-substituted derivatives. This conversion was carried out through the stage of obtaining potassium salt. Several chloroacetamides were tested as alkylating agents, which allowed to obtain the corresponding 2-(5,7-dimethyl-2-oxo-thiazolo[4,5-b]pyridin-3-yl)-N-aryl-acetamides (1–6). Methods of quantitative elemental analysis, mass spectrometry, and 1H NMR spectroscopy were used to confirm the structure and individuality of the synthesized substances. Interpretation of the spectra revealed that the signals for protons of all structural units were observed in their characteristic ranges.
Mounting research has been performed in the recent decades focusing on natural and low-molecular-weight synthetic antioxidants discovering as key molecules that control oxidative damage and its pathway to disease.
Oxidative stress is a phenomenon resulting from the imbalance between oxidation-reduction processes, in particular, the formation and accumulation reactive oxygen species (ROS) and reactive nitrogen species (RNS) in cells and tissues, and the ability of the antioxidant defence system of the organism to eliminate these by-products. Oxidative stress develops under the influence of external or internal factors and leads to oxidative modification of biomolecules, in particular lipids, proteins and DNA [6]. One- and two-electron oxidation-reduction reactions, as an integral part of aerobic metabolism, often lead to free radicals’ in vivo formation. Molecular oxygen reduction processes include the stepwise single electron reduction of O2 results in such ROS generation as superoxide anion radical (O2•-), hydrogen peroxide (H2O2) and hydroxyl radical (HO•). H2O2 is produced as a result of two-electron O2 reduction. Reactive nitrogen species include mainly nitric oxide (NO•), nitrogen dioxide (NO2•) and peroxynitrite (ONOO−), as well as non-radicals such as nitrous acid HNO2 and N2O4 (dinitrogen tetroxide).
At lower concentrations ROS/RNS have beneficial effects and indulged in different physiological processes such as redox regulation, mitogenic responses, cellular signaling pathways, and an immune function while at a higher level, these reactive species generate nitrosative and oxidative stress.
In modern research the two main types of antioxidants are distinguished: (1) the primary antioxidants, or free radical scavengers, which are able to break the chain reaction; (2) the secondary, or preventive, antioxidants, for which the action mechanisms may include the deactivation of metals, inhibition of lipid hydroperoxides by interrupting the production of undesirable volatiles, the regeneration of primary antioxidants, and the elimination of singlet oxygen. The methods of the antioxidant capacity determining are commonly classified into two main groups, based on the reaction mechanisms involved in free radicals’ reduction process: (a) hydrogen atom transfer (HAT) reactions; and (b) transfer reactions of a single electron (SET).
Nowadays the discovery of effective antioxidant agents among low-molecular-weight organic molecules is a recent problem that requires new methodological approaches implementation, while it is also the society relevant task [1]. Both thiazole and pyridine scaffolds are of the highest priority in modern medicinal chemistry [2, 3]. Numerous reports concerning variety biological effects possessed by thiazolopyridine derivatives have been currently published including their discovery as potent antioxidant agents [4].
One of the antioxidant action mechanisms can be exerted through the inhibition enzymes’ activity which are responsible for reactive oxygen species (ROS) producing, thereby reducing oxidative stress. The objective of the precent study was to fulfil molecular docking studies of novel 3H-thiazolo[4,5-b]pyridine-2-one derivatives towards lipoxygenase (LOX) as one of ROS-producing enzymes. LOX-5 is the enzyme that catalyses the oxidation of polyunsaturated fatty acids to form lipid hydroperoxides, which can lead to membrane damage and inflammation.
The objects of the precent research were three series of condensed 3H-thiazolo[4,5-b]pyridine derivatives, synthesized at Danylo Halytsky Lviv National Medical University [5-7]: (a) the 1st series included N3 substituted derivatives containing phenyl, propanenitrile, propanoic acid and phenylpropanamide moieties as N3-substituents while they comprised hydroxyl group at C5 position; (b) the 2nd series comprised compounds incorporated substituted phenyl diazonium or alkyl substituents at C6 position of the core scaffold; (c) the 3rd series included derivatives incorporated chloroacetate, chlorobenzoate, benzyloxybenzoate, methoxyphenyl acrylate and substituted phenyltriazolecarboxylate moieties as the substituents at C5 position of the core scaffold (Fig. 1). The antioxidant activity evaluation of all tested compounds was reported as a spectrophotometric DPPH assay based on the ability of antioxidant drug candidates possess free radical scavenging potency. Compounds of all three series were found to exhibit moderate and low antioxidant effects.
Probing the action mechanism of 3H-thiazolo[4,5-b]pyridin-2-one derivatives as antioxidants was performed through molecular docking studies towards lipoxygenase. Docking studies, filtering and poses grouping according to the Estimated Affinity towards the biotarget were carried out using SeeSar13.1.0 software (BioSolveIT, Sankt Augustin, Germany) [8]. The crystal structures of lipoxygenase were downloaded from Protein Data Bank using the Protein Mode of the software. Two structures of LOX-5 were downloaded: PDB entry 3O8Y - a 2.39 Å resolution structure of LOX-5 without ligands; PDB entry 6N2W – a 2.71 Å resolution structure of LOX-5 with co-crystallized ligand NDGA (Masoprocol, 4-[(2r,3s)-3-[(3,4-dihydroxyphenyl)methyl]-2-methylbutyl]benzene-1,2-diol).
Actuality. Discovery of innovative drug candidates is one of the relevant tasks of modern medical and pharmaceutical science. The thiazole core is a versatile scaffold for the development of new drugs and biologically active agents [1]. The recent publications, dealing with synthesis and pharmacological screening of thiazole-bearing heterocycles and their activity mechanisms [2-4], indicate the relevance of further drug discovery among novel derivatives of the specified chemical class.
The objectives. The precent work is devoted to the systematic study and generalization of the main trends in the field of potential antimicrobial drug candidates development of among condensed thiazolo[4,5-b]pyridine derivatives.
Materials and methods. The complex of general scientific methods of searching and systematizing literary references, analysis and comparison of information from various sources was used, followed by generalization of new and promising directions.
Results. Thiazolo[4,5-b]pyridine derivatives have been extensively evaluated as antimicrobial agents. Abd El-Mahmoud reported antimicrobial and antifungal screening for 5-amino-2-thioxo-2,3,4,7-tetrahydro-1,3-thiazolo-[4,5-b]pyridine-6-carbonitriles [5]. All compounds showed moderate antimicrobial activity against Staphylococcus aureus (St). Some compounds from this series showed moderate antimicrobial activity against Bacillus subtilis (B.C.) and Proteus vulgaris (P. vulgaris). The lead compound was highly active against Aspergillus flavus (A. flavus).
El-Sofany et al.reported in vitro antimicrobial and antifungal activity evaluation of novel spiro[cyclohexane-1,2'-thiazolo[4,5-b]pyridine derivatives [6]. SAR analysis revealed that open-chain sugar moieties introduction played a significant role in antimicrobial activity increasing. It was also shown that acetylated aldoses were less active than non-acylated ones and the activity increased by increasing the number of -OH groups rather than -OAc groups in the open-chain sugar nucleus.
Lozynsky et al. reported antimicrobial activity in vitro evaluation for 5,7-substituted 3H-thiazolo[4,5-b]pyridin-2-ones [7]. It was shown that the antibacterial effect did not depend on the substituents at C5 and C7 positions. The presence of amide fragment was favorable for antimicrobial potency.
Conclusions. The current trends in discovery of new active pharmaceutical ingredients among condensed thiazolo[4,5-b]pyridine derivatives exhibiting antimicrobial activity was based on structural modification strategy of the core condensed scaffold at C2, C5, C6, and C7 positions followed by pharmacological screening.
Acknowledgement: O. K. thanks Universidad San Pablo CEU for a Postdoctoral Contract for Ukrainian Researchers 2022-2024.
Actuality. The development of anti-inflammatory drugs occupies an important role in the field of modern pharmacology. Cyclooxygenases (COX-1 and COX-2) are the key enzymes involved in the arachidonic acid cascade. Classical non-steroidal anti-inflammatory drugs (NSAIDs) are diverse group of compounds used for the treatment of inflammation exerting their anti-inflammatory, analgesic, and antipyretic effects through the non-selective inhibition of both COX isoforms. In the past decade fused thiazole-based derivatives became an integral part of new anti-inflammatory agents’ discovery. A wide range of synthetic thiazole-bearing derivatives have been studied for their anti-inflammatory properties including COX-1/COX-2 inhibitory action [1].
The objectives. Introduction of molecular modeling methods within the computer-aided drug discovery process allows to minimize the time and costs for construction and development of new biologically active substances and may accelerate and facilitate the identification of novel COX-1/2 inhibitors among fused thiazole-scaffold bearing compounds.
Materials and methods. The objects of the precent research were three series of 37 N3, C5 and C6 substituted 3H-thiazolo[4,5-b]pyridine-2-one derivatives, synthesized at Danylo Halytsky Lviv National Medical University. Probing the action mechanism of thiazolopyridines as anti-exudative agents was performed through molecular docking studies towards COX1/2. Docking, filtering and poses grouping according to the Estimated Affinity were carried out using SeeSar13.1.0 software [2].
Results. The structures of COX-1 in complex with Celecoxib (PDB entry 3KK6) and human COX-2 in complex with Rofecoxib (PDB entry 3KK6) were downloaded from Protein Data Bank. Co-crystalized ligands were extracted from the binding sites. Docking of the set of 37 ligands, Mefenamic acid and Ibuprofen as references were carried out utilizing two workflows: Standard docking and Template Docking. Visual inspection of poses and their Lipophilic Ligand efficiency (LLE) evaluation led us to choose Template docking outcomes with Ibuprofen as the template for further analysis. All poses were checked and transferred to the Analyzer Mode. Molecules were grouped by the pose of each compound with the best estimated activity. The analysis of docking results against COX-1 allowed to conclude, that all docked ligands had the proper orientation in the binding site of COX-1, most common amino acid residues of the protein for hydrogen binding with ligands were ARG-120 and SER-530, the HYDE scores of the most active ligands exceed that ones for Celecoxib.
Docking results against COX-2 revealed that hydrogen bonds in most ligand-receptor complexes were formed between Oxygen atom of thiazole ring and TYR-355 amino acid residue. Favourable HYDE scores corresponded to Sulfur atom of thiazole ring and/or C3 and C5 carbons of phenyl substituent in N3 position of fused scaffold contributions. Non-favorable contributions referred to Oxygen atom of thiazole ring. At the same time, in both docking procedures for the ligands under study their Estimated Affinity towards COX-2 was significantly lower than that one for Ibuprofen despite they were able to achieve proper orientations.
Conclusions. The number of hit compounds under study showed high Estimated Affinity, proper binding orientation and significant HYDE scores towards proposed protein targets. However, no exact correlation between experimental pharmacological activities and docking scores was found.
Acknowledgement: O. K. thanks Universidad San Pablo CEU for a Postdoctoral Contract for Ukrainian Researchers 2022-2024.