HERBICIDE BRAND NAMES, ACTIVE INGREDIENTS, CHEMICAL FAMILIES, AND MODES OF ACTION (continued) Brand Names Active Ingredient(s) Chemical Family Mode of Action1 Corvus thiencarbazone + isoxaflutole Triazolone + isoxazole 2. Herein, we report the discovery and structure–activity relationships of 5-substituted-2-. The majority of these. Synthesis, Characterization, Antimicrobial Potential, and Computational Studies. M. College of Pharmacy, Maharishi Markandeshwar University, Mullana, Ambala, Haryana 1. India. 2Shivalik College of Pharmacy, Nangal, Punjab 1. India. Received 1. February 2. 01. 4; Revised 3 April 2. Accepted 6 April 2. Published 2. 4 July 2. Copyright . This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. We report the synthesis and biological assessment of 1,3,4- oxadiazole substituted 2. The structures of the newly synthesized derivatives were established by the combined practice of UV, IR, 1. H NMR, 1. 3C NMR, and mass spectrometry. Further these synthesized derivatives were subjected to antibacterial activity against all the selected microbial strains in comparison with amoxicillin and cefixime. The antibacterial activity of synthesized derivatives was correlated with their physicochemical and structural properties by QSAR analysis using computer assisted multiple regression analysis and four sound predictive models were generated with good , , and Fischer statistic. The derivatives with potent antibacterial activity were subjected to molecular docking studies to investigate the interactions between the active derivatives and amino acid residues existing in the active site of peptide deformylase to assess their antibacterial potential as peptide deformylase inhibitor. Introduction. Oxadiazoles are the heterocyclic compounds containing one oxygen and two nitrogen atoms in a five membered ring . Oxadiazole is considered to be resultant from furan by replacement of two methane (–CH=) groups by two pyridine type nitrogen atoms (–N=) . Several methods have been reported in the literature for the synthesis of 1,3,4- oxadiazoles. Available on line www.jocpr.com Journal of Chemical and Pharmaceutical Research . Res., 2011, 3(2):126-133 126 Recent advancement. The commonly used synthetic route for 1,3,4- oxadiazoles includes reactions of acid hydrazides (or hydrazine) with acid chlorides/carboxylic acids and direct cyclization of diacylhydrazines using a variety of dehydrating agents such as phosphorous oxychloride . These differences may be attributed to the fact that the cell wall in gram positive bacteria is of single layer whereas the gram negative bacteria have multilayered cell wall. Gram negative bacteria possess an outer membrane and a unique periplasmic space which is not found in gram positive bacteria . The resistance of gram negative bacteria towards antibacterial substances is due to more lipophilic nature of membrane, which acts as a barrier for various antimicrobial compounds. It was expected that hydrophilic compounds are unable to penetrate the cell membranes of these bacteria. Gram positive bacteria do not have such outer membrane and complex cell wall structure. Antibacterial substances can easily destroy the bacterial cell wall and cytoplasmic membrane of gram positive bacteria, which results in leakage of the cytoplasm . It embraces iron and is responsible for protein maturation by the exclusion of the N- formyl group from the terminal methionine residue through Fe.
There are numerous areas of computational studies and one of them is identification of relationships between chemical structures and properties and recognized as QSAR. Quantitative structural activity relationship practices molecular parameters to enumerate a pharmacological or chemical property for a set of molecules . It makes an image of the dynamic site with interaction points known as grid. Then it fits the ligand in the binding site either by grid search or energy search . Chemistry. The substituted aromatic acids were used as a versatile starting material for the synthesis of 1,3,4- oxadiazoles derivatives involving the formation of corresponding esters and hydrazides. Ethyl esters were synthesized from substituted aromatic acids by means of Fischer esterification which were further reacted with hydrazine hydrate in presence of ethanol to get corresponding hydrazide derivative. The hydrazide derivatives then reacted with . The chemistry of compounds 8a–h was already reported in our previous studies . The substituted aromatic acid hydrazides from o- benzoyl benzoic acid reacted with aromatic aldehydes under slight acidic conditions to get the substituted hydrazone derivatives which were then cyclized in presence of bromine, acetic acid, and sodium acetate to get 1,3,4- oxadiazole derivatives (1. Figure 2). Reaction monitoring was done by means of thin layer chromatography (TLC). All the new synthesized compounds were characterized by melting point and spectroscopic analysis (UV- Visible, IR,1. H NMR, 1. 3C NMR, and MS). Figure 1: Synthetic scheme of 1- (4- methoxy- phenyl)- 3- . Experimental Section. Material and Method. Reagent and solvents used were obtained from commercial sources. Analytical thin layer chromatography was carried out on TLC plates of coated with silica gel G for reaction monitoring and for determination of retardation factor. Spots of TLC were located by iodine chamber. Melting points of newly synthesized derivatives were determined on digital melting point apparatus (Flora; Perfit, India) and were found uncorrected (Table 2). The was calculated by using double beam UV- Visible 1. Shimadzu spectrophotometer and the values are given in Table 2. The IR spectra were recorded on FTIR- Shimadzu spectrometer using Nujol method. H NMR and 1. 3C NMR spectra were recorded on BRUKER AVANCE II 4. NMR spectrometer operating at 4. MHz and 1. 25 MHz, respectively, using CDCl. For mass spectra, solutions were made in HPLC grade methanol and spectra were obtained with Vg- 1. J7. 0S spectrophotometer at 7. V using electron ionization (EI source). Chem 3. D Ultra (version 1. QSAR studies were performed by multiple linear regression analysis using Analyze- it version 3. Molegro Virtual Docker 5. General Procedure for the Synthesis of 1- (4- Methoxy- phenyl)- 3- (5- phenyl- 1,3,4- oxadiazol- 2- yl)propan- 1- one (6a–h)Aryl hydrazide 2a (1 M) was dissolved in phosphorous oxychloride (5 m. L) and to it compound 5 (equimolar; 1 M) was added. The reaction mixture, after refluxing for 6- 7 hours, was cooled to room temperature and poured onto crushed ice. On neutralization of the contents with sodium bicarbonate solution (2. This was filtered and washed with water. It was crystallized by using methanol to give 6a. Similarly compounds (6b–h) were prepared (Figure 1) . The corresponding R for 6a–h is given in Table 1. Table 1: Substituted groups (R) of different synthesized compounds. Table 2: Physical properties and UV- Visible analysis of synthesized 1,3,4- oxadiazole derivatives. Methoxy- phenyl)- 3- (5- phenyl- 1,3,4- oxadiazol- 2- yl)propan- 1- one (6a)Yield 8. Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . Methoxy- phenyl)- 3- . General Procedures for the Synthesis of . Bromine (0. 8 m. L in 5 m. L of glacial acetic acid) was added slowly to it while stirring magnetically. After 2 hours of stirring the solution was poured on crushed ice. The resulting solid was separated, dried, and recrystallized from ethyl alcohol. Similarly compounds (1. Figure 2) . The corresponding R for 1. Table 1. 3. 3. 1. Antibacterial Evaluation. Antibacterial Activity. The antibacterial evaluation was carried out by using agar cup- plate method. The microorganisms Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, and Staphylococcus aureus were used for the antibacterial evaluation. Nutrient agar media were prepared and then inoculated with fresh prepared culture media. The inoculated media were poured into Petri dish and allowed to set. Cups were made by punching the agar surface with a sterile cork bore (8 mm). Solutions containing 1. Amoxicillin and cefixime were taken as positive control and DMF was taken as blank. The plates were incubated at 3. The zones of inhibition of the microbial growth produced by different concentration of test compounds were measured in millimeters . The zone of inhibition data for antibacterial compounds is summarized in Table 3. Table 3: Zone of inhibition of synthesized 1,3,4- oxadiazole derivatives against selected microbial strains. Minimum Inhibitory Concentration (MIC)Nutrient agar was prepared, sterilized, and cooled to 4. It was inoculated with 0. L of culture and mixed well by gentle shaking before pouring into the sterilized petri dishes. The poured materials were allowed to set and thereafter the cups were made by punching into the agar surface with sterile cork borer and scooping out the punched part of the agar. L of each test compounds was added into the cups with the help of sterile syringe. Twofold diluted solutions of the compounds and reference drugs were used (6. The drug solutions were allowed to diffuse for some time into the medium. The plates were incubated at 3. The incubation chamber was kept sufficiently humid. MIC values were determined at the end of the incubation period. The MIC values for synthesized compounds are summarized in Table 4 and graphical representation of MIC of synthesized 1,3,4- oxadiazole derivatives and standard drugs against gram negative and gram positive bacterial strains are given in Figures 3 and 4 (Table 4), respectively . QSAR Analysis. The compounds were analyzed by multiple regression analysis, a QSAR approach using different physicochemical parameters as independent and biological activity as dependent variables . Multiple linear regression efforts to maximize the fit of the data to a QSAR model for the biological activity by correcting each of the existing parameters. Successive regression models will be generated in which parameters will be either added or removed until the maximum and minimum S are obtained. The extent of coefficients obtained in this routine specifies the virtual contribution of the associated parameters to biological activity. Biological activity data was converted to the logarithmic value.
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