Design and Synthesis of Novel Bis Thiazolo[4,5-c ]Isoxazolines Bearing 1,2,4-triazole Ring Derived From the Related 4-thiazolidinons as Antimicrobial Agents

Design and synthesis of novel poly heterocycles together using same heterocyclic compound is the main task of the present paper. The target compounds entitled 4,4’-[benzene-1,4-diylbis[ethylidenehydrazine-2-ylidene]bis[4-[3,5-di(5-substitutedpyridin-2-yl)-3,3a-dihydro[1,3]thiazolo[4,5-c][1,2]oxazol-6(5H)-yl]-4H- 3-yl-1,2,4-triazole-3-thiol] have been synthesized starting from the reaction of 1,4-diacetylphenyl and carbohydrazide to give Schiff base derivatives then 1,2,4-triazole derivatives from the reaction with CS 2 and an excess of hydrazine hydrate. The same applies for the condensing of these newly heterocyclic amines with different pyridine-2-carbaldehydes, which resulted in the synthesis of some new Schiff bases, which were then cyclized to develop new thiazolidinones by thioglycolic acid. Additionally, by fusing thiazolidinones with various pyridine-2-carbaldehydes, a novel chalcone was formed. To produce the desired fused isoxazolines, the later compounds underwent cyclization with hydroxylamine hydrochloride and potassium hydroxide. From the examination of the (CHN), FTIR, 1 H NMR, and 13 C NMR spectra, the structural identities of all recently synthesized compounds were determined. The newly synthesized chemicals were also successfully tested as an antibacterial agent.


Introduction
Due to microbial resistance to the majority of existing antimicrobial drugs, the treatment of microbial illnesses is the most exciting subject.A challenging scenario has arisen as a result of antibiotic resistance in microorganisms, necessitating the rapid design and development of novel antibiotics [1].Nevertheless, the five-membered heterocyclic compounds such as thiazoles and oxazoles are well-known and have a range of biological functions [2,3].Additionally, the thiazole nucleus is a fundamental component of all penicillin-based medications, which have revolutionized the way bacterial illnesses are treated [4].Additionally, isoxazolines are a significant class and have been shown to have potent antibacterial [2,3], antidiabetic [5], anthelmintic [6], diuretic [7,8] properties.Thus, the 1,3-thiazolidien-4-one ring system's chemistry is of importance since it serves as a fundamental component in several synthetic pharmaceuticals and has outstanding value for both their synthetic and biological features [9].Numerous thiazolidinone compounds have been synthesized and have shown to exhibit exceptional bioactivities, including antibacterial [10], antidiarrhoeal [11], anticancer [12].Due to their major function in organic and medicinal chemistry, there has been a surge in interest in the synthesis of novel heterocycles including isoxazole/isoxazoline derivatives in recent years.Following a review of the literature, many novel isoxazoline derivatives were synthesized using various techniques.However, novel isoxazoline compounds were produced by 1,3-dipolar cycloaddition of nitrile oxides with dialkyl maleate [13,14].In contrast, chalcones have been used to produce a number of novel mono-and twin-fused pyrazolone (indazol-3-one) and thioxopyrimidine derivatives [15].Similarly, hydroxylamine hydrochloride was used to react with chalcone derivatives to produce methylene-bistetrahydro [1,3]thiazolo [4,5-c]isoxazoles [10].In addition, novel isoxazoline compounds have been synthesized by reacting chalcones with hydroxyl amine hydrochloride in the presence of sodium hydroxide as a base [16].The condensation reaction of N-phenylhydroxylamine with various aldehydes was recently used to produce several novel isoxazolines under various circumstances [17].Only a few reports of the synthesis of an isoxazoline core fused with a thiazolo moiety were made as a result of these discoveries.Our overall approach in this study is to develop and synthesize novel triazolo [4,5-c]isoxazolines heterocycles and evaluate them for antibacterial properties in order to address this problem.

Materials and Methods
Without additional purification, all chemicals and reagents were used as they were acquired from their suppliers.By employing pre-coated metal plates with silica gel, thin layer chromatography was used to track the reaction's progress.On the Electrothermal SMP30 melting point equipment, melting points were recorded (and are uncorrected).The Fison 1108 (CHN) Elemental Analyzer was used to calculate percentages of (CHN) elements.For FTIR spectra, an 8400s FTFTIR-Shimadzu spectrophotometer was used with a (KBr) disc.Bruker spectrometer (300 MHz and 150 MHz, respectively) was used to outline 1 H NMR and 13 C NMR spectra in DMSO-d6 using TMS as internal standard reference.The chemical structures were drawn with CS Chem Draw Ultra (6.0) software.

Chemistry
Following the instructions in Scheme 1, a number of new fused heterocyclic compounds of bis thiazolo[4,5-c]isoxazoline derivatives carrying 1,2,4-triazole moieties have been synthesized.First, in an acidic solution, carbohydrazide and 1,4-diacetylphenyl 1 were condensed to produce dicarbohydrazide, 2. FTIR spectrum of 2, Figure 1 showed a new band at 1614 (C=N) stretching.Whereas, 1 H NMR reveals a singlet signals at 7.93-7.74which corresponding to the four protons of (CONH) group, Figure 2. The appropriate salt was then produced by treating 2 with CS2 in alcoholic KOH (and was not isolated), and by hydrazinolyzing 3 with too much hydrazine hydrate, new derivatives of bis (4-amino-4H-3mercapto-1,2,4-triazole) were formed.The disappearance of carbonyl group vibration in the FTIR spectrum of 3, as well as, a singlet signal due to aromatic-SH at 2.51has been appeared in proton NMR spectrum, Figures 3 and 4. Additionally, new Schiff base derivatives 4a-4d were produced by the direct condensation reaction of 3 with pyridine-2-carbaldehydes in the presence of glacial acetic acid as a catalyst.A coincidence structural confirmation for compounds 4a-4d were deduced from their spectroscopic data, especially by disappearance of primary amines vibrations as shown in Figures 5-8.These derivatives were then cyclized to produce new 4-thiazolidinone derivatives 5a-5d by reacting with thioglyolic acid under reflux conditions. 1 H and 13 C NMR Figures 10 and 11 showed a singlet signals at 6.88 ppm and 5.62 corresponding to C=CH Chalcone and CH thiazolidinone, respectively.Moreover, chalcones 6a-6d were produced by fusion reaction of 5a-5d with different pyridine-2-carbaldehyde in presence of piperidine as a base.Finally, the cyclization of 6a-6d with hydroxylamine hydrochloride and KOH in refluxing ethanol gave the target thiazolo [4,5-c]isoxazoline derivatives 7a-7d.Although the suggested mechanism of the preparation of isoxazolines remains to be clarified [21], nevertheless the proposed mechanism of the target compound could be explained as outlined in Scheme 2. Meanwhile, the intermediates B and C are produced as the initial stage of the Michael addition reaction between the 5-arylidine-4-thiazolidinone derivatives A and hydroxylamine hydrochloride, which is then further rearranged to create the intermediates D and E.Then, intramolecular cyclization and dehydration processes might be used to produce the final thiazolo [4,5-c]isoxazoline derivatives F. From the FTIR spectroscopy data (See experimental section), as well as from the physiochemical and microanalysis of C.H.N elements (Table 1), it has been determined that all compounds have coincidental structural confirmation, Figures 12-15.

Antimicrobial Investigation
Antimicrobial activity of 7a-7d and their related 4-thiazolidinones 5a-5d, 6a-6d were investigated for their biological properties against B. subtilis, S. Sciuri and E. coli, P. aeruginosa strains.Furthermore, these compounds were examined versus A. flavus and C. albicans as fungal strains.Diffusion method was applied for this investigation [22].In order to compare the studied compounds to the standard references of ciprofloxacin and ketoconazole, the examined compounds were dissolved in DMSO solvent to get (100 µg/mL).The plates were incubated for 24 hours at 37 °C for the bacterial culture.While the fungal culture was incubated at 25 °C and checked after 72 hours.Table 2 lists the satisfactory findings that were obtained.

Table 1 :
Physicochemical and microanalysis properties of the designed compounds