THE SYNTHESIS OF 4-THIAZOLIDINONE DERIVATIVES USING 2-(4-R-2-FORMYLPHENOXY)-N-(R’-PHENYL)ACETAMIDES AND THEIR ANTI-INFLAMMATORY ACTIVITY

The research is devoted to the rational design of new non-steroidal anti-inflammatory drugs (NSAIDs) using the 4-thia- zolidinone “core”. A series of 2-(4-R-2-formylphenoxy)-N-(R’-phenyl)acetamides has been synthesized from salicylic aldehydes for structural modifications of basic heterocycles. The aldehydes obtained are active carbonyl agents and suitable “building blocks” for the focused synthesis of biologically active compounds. Ylidene derivatives of 2-thioxo-4-thiazolidinone and 2-(4-hydroxyphenyl)imino-4-thiazolidone have been synthesized in the Knoevenagel reaction conditions. The one-pot reaction between 3(5)-merkapto-1,2,4-triazoles, chloroacetic acid and the salicylic aldehyde derivatives synthesized have been used for the synthesis of 5-ylidene-thiazolo[3,2-b][1,2,4]triazol-6-one. Parameters of acute toxicity and the anti-exudative activity (carrageenin paw edema test) have been studied for the ylidene derivatives synthesized. It has been found that all compounds synthesized demonstrate the anti-exudative activity, and some “structure – acute toxicity – anti-exudative activity” relationships have been analyzed. Based on the results of in vivo studies the lead compound – 4-{2-[4-chloro-2-(6-oxothiazolo[3,2-b][1,2,4]triazole-5-ylidenemethyl)-phenoxy]- acetylamino}-benzoic acid ethyl ester that demonstrates the anti-exudative activity equivalent to the classic NSAID Diclofenac has been identified, it has a low level of toxicity and can be recommended for the profound study.


ISSN 2308-8303
Non-steroidal anti-inflammatory drugs (NSAIDs) are one of the oldest and most widely used groups of drugs today [1]. There are more than 20 original monocomponent NSAIDs, about 200 generics and a significant number of combined drugs and their generic versions at the Ukrainian pharmaceutical market [2]. However, the problem of searching and creating new NSAIDs remains open, primarily to eliminate gastrointestinal, cardiovascular and renovascular risks in their long-term use [3][4][5]. Drugs affect the cellular metabolism of arachidonic acid, which is a substrate for the synthesis of active intracellular intermediates, eicosanoids, leukotrienes and others, and is the key mechanism for therapeutic and adverse effects of different classes of NSAIDs [6]. Organic compounds from different classes [7][8][9], including 4-thiazolidinone derivatives [10][11][12][13], can change the phospholipase A2 activity blocking the process of arachidonic acid releasing from cell membranes phospholipids; selective and non-selective inhibit cyclooxygenases types 1 and 2 (COX-1 and COX-2) and thus prevent the arachidonic acid transformation to eicosanoids; inhibit 5-lipoxygenase (5-LOX) preventing the arachidonic acid conversion to leukotrienes; demonstrate multiactivity against the enzyme systems (COX-2/5-LOX dual inhibitors), etc. According to the modern concepts PPAR-receptors play an important role in the cellular mechanisms of inflammatory processes [14]. It is known that 4-thiazolidinones are "classic" high affinity ligands for PPARγ-receptors [15].
The systematic research in the field of potential NSAIDs synthesis and screening among 4-thiazolidinone derivatives is the priority direction for the research group of the Department of Pharmaceutical, Organic and Bioorganic Chemistry at Danylo Halytsky Lviv National Medical University [16][17][18][19][20][21]. The qualitative and quantitative "structure -antiinflammatory activity" databases obtained for 4-thiazolidinones allow to carry out the rational structural design of the 4-thiazolidinone "core" for searching new potential NSAIDs. The aim of this research was the synthe-sis of 5-ylidene-4-thiazolidinones from 2-(4-R-2-formylphenoxy)-N-(R'-phenyl)acetamides, as well as the study of their anti-exudative activity and acute toxicity.
The structure of the compounds synthesized was confirmed by 1 H-NMR spectra. Protons of CH 2 -CH fragments in the pyrazoline ring of compounds 6 and 13 form a characteristic AMX system due to their diastereoisomerism. This system appears in 1 H-NMR spectra as three duplicate doublets at 3.30-3.40, 4.00-4.15 and 5.70-5.90 ppm with constant J AM = 17.8-18.0, J Ax = 10.7-10.9 and J Mx = 3.0-3.8 Hz.
The acute toxicity was studied in order to assess the prospects of the compounds synthesized as biologically active substances. Pastushenko's expressmethod was used for determination of acute toxicity parameters [22]. White mice of both sexes weighing 20-27 g were used for the experiment. The animals were kept on a standard diet with a free access to food and water during the experiment. The test compounds were dissolved in Tween-80 and purified water and introduced intraperitoneally. The observation of the animals was performed for 14 days. The LD 50 values determined for the test substances (Fig. 3) were higher or equivalent to the LD 50 of the reference drug Diclofenac and allowed to refer them to moderately  (7) and low-toxic (8-13) compounds according to K. K. Sidorov classification (the III and IV class of toxicity) [23]. In the analysis of the "structure -acute toxicity" relationship it has been found that higher levels of LD 50 have the following compounds: the annelated derivative of 4-thiazolidinone (10) containing the unsubstituted amide function (11) or the diphenylpyrazoline moiety (13) in the ylidene fragment, while derivatives 7-9, 12 with N-(R'-phenyl)chloroacetamides substituents in the molecule are more toxic.
The carrageenin paw edema test was used for the anti-exudative activity screening of the compounds synthesized [24]. The inflammatory edema of the paw was generated by injection of 0.05 ml 1% carrageenin solution (Sigma) into the right hind limb of the mice [25]. The compounds and reference drug were administered intraperitoneally one hour before the carrageenin injection in the doses of 0.05 LD 50 . The control group of animals was administered an equivalent amount of the solvent. Animals were taken out from the experiment by the cervical vertebrae dislocation at 3 hr after injecting carrageenan (at the peak of action) and limbs masses were measured and compared after disarticulation at the hip joints. The results of AEA screening (Fig. 3) demonstrate that all compounds synthesized are active. The range   The general procedure for the synthesis of ylidene derivatives 7-9 and 11-13. Reflux the mixture of the appropriate oxocompounds 1-3 or 5-6 (10 mmol), 2-thioxo-4-thiazolidinone (7-9, 11, 13) or 2-(4-hydroxyphenyl)imino-4-thiazolidinone (12) (10 mmol) and anhydrous sodium acetate (15mmol) for 2 h in a glacial acetic acid (5 ml). Filter the powders obtained, wash with ethanol and recrystallize with the corresponding solvent.