Chapter 2 EXPERIMENTAL 2.1. SYNTHESIS OF 1-(1-(4-ISOBUTYLPHENYL)ETHYLIDENE)- THIOSEMICARBAZIDE (121) A mixture of 4 -(2-methylpropyl) acetophenone (0.01 mol) and thiosemicarbazide (0.015 mol) were treated with 50 ml of methanol with few drops of concentrated hydrochloric acid. The reaction mixture was refluxed for 2 hrs on a water bath. The progress of the reaction was monitored through TLC. After the completion of reaction, the contents were cooled and the solids separated were filtered. Recrystallization of the compound in hot ethanol furnished 90% of the pure 1-(1-(4-isobutylphenyl)ethylidene) thiosemicarbazide. 2.1.1. Synthesis of 1-(1-(4-isobutylphenyl)ethylidene)-2-(4- phenylthiazol-2-yl)hydrazines (122-127) General procedure: In a dry 100 ml round bottom flask, 1-(1-(4-isobutylphenyl)ethylidene)thiosemicarbazide 121 (0.0025 mol) and 2-bromoacetophenone/4-substituted 2-bromoacetophenone (0.0025 mol) in 50 ml of isopropanol were refluxed for 2-4 hrs to obtained dark brown solids. Progress of the reaction was monitored by TLC by eluting with benzene. After the completion of reaction, the mixture was cooled in ice bath and basified with ammonium hydroxide
27 to the neutral ph. The crude product was filtered and purified by column chromatography on silica gel 60 (230 400 mesh ASTM), using chloroform eluent system. The fractions containing product were collected and concentrated under reduced pressure, yielded the corresponding thiazolylhydrazones. following compounds. The above general method is adopted for the synthesis of i) 2-(4-(4-Cyanophenyl)thiazol-2-yl)-1-(1-(4-isobutylphenyl)- ethylidene)hydrazine (122) ii) 2-(4-(4-Fluorophenyl)thiazol-2-yl)-1-(1-(4-isobutylphenyl)- ethylidene)hydrazine (123) iii) 2-(4-(4-Chlorophenyl)thiazol-2-yl)-1-(1-(4-isobutylphenyl)- ethylidene)hydrazine (124) iv) 2-(4-(4-Bromophenyl)thiazol-2-yl)-1-(1-(4-isobutylphenyl)- ethylidene)hydrazine (125) v) 1-(1-(4-Isobutylphenyl)ethylidene)-2-(4-phenylthiazol-2- yl)hydrazine (126) vi) 1-(1-(4-Isobutylphenyl)ethylidene)-2-(4-(4-methoxyphenyl)- thiazol-2-yl)hydrazine (127)
28 2.2. SYNTHESIS OF 1-(2-METHYL-3-PHENYLALLYLIDENE)- THIOSEMICARBAZIDE (128) To a mixture of 2-methyl-trans-cinnamaldehyde (0.01 mol) and thiosemicarbazide (0.0125 mol) dissolved in 50 ml of methanol, two drops of concentrated hydrochloric acid were added. The reaction mixture was refluxed for 2 hrs using water bath. The progress of the reaction was monitored by TLC. After the completion of reaction, the contents were cooled to room temperature and the obtained solid was filtered and washed with warm water to remove the excess amount of thiosemicarbazide and impurities. The crude product was purified by recrystallizaton using ethanol solvent, yielded colourless solid. 2.2.1. Synthesis of 1-(2-methyl-3-phenylallylidene)-2-(4- phenylthiazol-2-yl)hydrazines (129-135) General procedure: A mixture of 1-(2-methyl-3- phenylallylidene)thiosemicarbazide 128 (0.005 mol) and 2-bromo- acetophenone/4-substituted 2-bromoacetophenone (0.005 mol) dissolved in 25 ml of isopropanol was refluxed until completion of the reaction. Progress of the reaction was monitored by TLC by eluting with benzene. After the completion of reaction, the mixture was cooled in ice bath and basified with ammonium hydroxide to the neutral ph. The solid was filtered off, dried and recrystallized from absolute ethanol to get the compound.
29 following compounds. The above general method is adopted for the synthesis of i) 1-(-2-Methyl-3-phenylallylidene)-2-(4-phenylthiazol-2-yl)hydrazine (129) ii) 2-(4-(4-Cyanophenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (130) iii) 2-(4-(4-Fluorophenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (131) iv) 2-(4-(4-Chlorophenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (132) v) 2-(4-(4-Bromophenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (133) vi) 2-(4-(4-Methylphenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (134) vii) 2-(4-(4-Methoxyphenyl)thiazol-2-yl)-1-(-2-methyl-3-phenylallylidene)- hydrazine (135) 2.3. SYNTHESIS OF 1-(3-PHENOXYBENZYLIDENE)THIOSEMICARBAZIDE (136) To a mixture of 3-phenoxybenzaldehyde (0.01 mol) and thiosemicarbazide (0.015 mol) were treated with 50 ml of methanol with few drops of concentrated hydrochloric acid were added. The reaction mixture was refluxed for 3 hrs using water bath. The progress of the reaction was monitored through TLC by eluting with benzene.
30 After the completion of reaction, the contents were cooled and the separated solids were filtered. The crude product was filtered, purified by recrystallization using absolute ethanol solvent. 2.3.1. Synthesis of 2-(3-phenoxybenzylidene)-1-(4-phenylthiazol-2- yl)hydrazines (137-143) General procedure: An equi-molar mixture of 1-(3-phenoxy- benzylidene)thiosemicarbazide 136 (0.01 mol) and 2-bromoacetophenone/4-substituted-2-bromo acetophenone (0.01 mol) in 50 ml of ethanol was refluxed for 4 hrs to obtained beige solid. Progress of the reaction was monitored by TLC by using with chloroform eluent systems. After the completion of reaction, the mixture was cooled in ice bath and basified with ammonium hydroxide to the neutral ph. The solid product was separated and washed with plenty of water and recrystallized using absolute ethanol. following compounds: The above general method is adopted for the synthesis of i) 2-(3-Phenoxybenzylidene)-1-(4-(4-bromophenyl)thiazol-2-yl)- hydrazine (137) ii) 2-(3-Phenoxybenzylidene)-1-(4-(4-fluorophenyl)thiazol-2-yl)- hydrazine (138) iii) 2-(3-Phenoxybenzylidene)-1-(4-(4-chlorophenyl)thiazol-2-yl)- hydrazine (139)
31 iv) 2-(3-Phenoxybenzylidene)-1-(4-(4-cyanophenyl)thiazol-2-yl)- hydrazine (140) v) 2-(3-Phenoxybenzylidene)-1-(4-phenylthiazol-2-yl)hydrazine (141) vi) 2-(3-Phenoxybenzylidene)-1-(4-p-tolylthiazol-2-yl)hydrazine (142) vii) 2-(3-Phenoxybenzylidene)-1-(4-(4-methoxyphenyl)thiazol- 2-yl)hydrazine (143) 2.4. SYNTHESIS OF 1-(3-FLUORO-2-HYDROXYBENZYLIDENE)- THIOSEMICARBAZIDE (144) In a dry 250 ml round bottom flask a mixture of 3-fluoro- salicylaldehyde (0.03 mol) and thiosemicarbazide (0.035 mol) was treated with 100 ml of methanol with few drops of concentrated hydrochloric acid were added. The reaction mixture was refluxed for 3 hrs to obtain pale yellow solid. The progress of the reaction was monitored through TLC by eluting benzene-ethylacetate (3:1 ratio). After the completion of reaction, the contents were cooled and solvent was removed under reduced pressure. The crude product was dried and purified by recrystallization with absolute ethanol. 2.4.1. Synthesis of 2-(3-fluoro-2-hydroxybenzylidene)-1-(4- phenylthiazol-2-yl)hydrazines (145-150) In a dry 100 ml round bottom flask a mixture of 1-(3- fluoro-2-hydroxybenzylidene)thiosemicarbazone 144 (0.01 mol) and 2-bromoacetophenone/4-substituted 2-bromoacetophenone (0.01 mol)
32 in 50 ml isoprapanol were refluxed for 4 hrs to obtain brown solid. Progress of the reaction was monitored by TLC by eluting with benzene. After the completion of reaction, the mixture was cooled in ice bath and basified with ammonium hydroxide to the neutral ph. The crude product was filtered, dried and purified by recrystallization from absolute ethanol. following compounds: The above general method is adopted for the synthesis of yl)hydrazine (145) ii) yl)hydrazine (146) iii) 2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-4-bromophenylthiazol-2- yl)hydrazine (147) iv) yl)hydrazine (148) v) 2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-4-methylphenylthiazol-2- yl)hydrazine (149) vi) i) 2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-4-cyanophenylthiazol-2-2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-4-fluorophenylthiazol-2-2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-phenylthiazol-2-2-(3-Fluoro-2-hydroxybenzylidene)-1-(4-4-methoxyphenylthiazol-2- yl)hydrazine (150)
33 2.5. GENERAL PROCEDURE FOR THE SYNTHESIS OF N-AROYL- HYDRAZIDES (151-154) A mixture of benzohydrazide (0.01 mol) and appropriate aldehyde (0.01 mol) in 25 ml of ethanol was stirred under reflux until solid precipitate formation (1-3 hrs). Progress of the reaction was monitored by TLC by eluting with chloroform-ethanol (9.5:0.5). After the completion of reaction, the mixture was cooled to room temperature, and the formed solid product was filtered off and the crude product was purified by recrystallization from a minimum amount of ethanol to give the desired product. following compounds. The above general method is adopted for the synthesis of i) N -[-Biphenyl-4-ylmethylidene]benzohydrazide (151) ii) N -(4-(Methylthio)benzylidene)benzohydrazide (152) iii) N -(3-Fluoro-2-hydroxybenzylidene)benzohydrazide (153) iv) N -(4-Bromo-3-hydroxy-2-methoxybenzylidene)benzohydrazide (154)
34 2.5.1. General procedure for the synthesis of 3-acetyl-2,5-diaryl-2,3- dihydro-1,3,4-oxadiazoles (155-158) In a dry 50 ml round bottom flask N-aroylhydrazones 151-154 (0.005 mol) were dissolved in 15 ml of acetic anhydride. The whole mixture was refluxed for 3-5 hrs and the progress of the reaction was monitored through TLC by eluting chloroform-ethanol (9:1 ratio). After the completion reaction, the mixture was left to cool down to room temperature. The excess acetic anhydride was distilled out at reduced pressure and the residue obtained was poured into ice cold water. The solid separated out was filtered, washed with water and dried. The crude product was recrystallized from hot ethanol to get pure compound. following compounds: The above general method is adopted for the synthesis of i) 1-[2-(Biphenyl-4-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl]ethanone (155) ii) ethanone (156) iii) 1-(2-(4-(Methylthio)phenyl)-5-phenyl-1,3,4-oxadiazol-3(2H)yl)- 1-(2-(3-Fluoro-2-hydroxyphenyl)-5-phenyl-1,3,4-oxadiazol- 3(2H)-yl)ethanone (157) (iv). 1-(2-(3-Bromo-4-hydroxy-5-methoxyphenyl)-5-phenyl-1,3,4- oxadiazol-3(2h)-yl)ethanone (158)
35 2.6. SPECTRAL MEASUREMENTS The structure of all the synthesized compounds are established by recording IR spectra, on AVATAR 360 FT-IR spectrometer [Thermo Nicolet)/Thermo Nicolet is5 FT-IR spectrometer using potassium bromide (KBr) pellets in range of 4000-400 cm 1 ] and the wave numbers are given in cm 1. The 1 H and 13 C NMR and 2D NMR (HOMOCOSY, HSQC and HMBC) spectra were recorded on a Bruker AMX 500 and 125 MHz Bruker AVENCE 400 and 100 MHz NMR spectrometer, respectively. All the NMR measurements were made on 5 mm NMR tubes. For recording 1 H NMR spectrum, solutions were prepared by dissolving about 10 mg of the compound in 0.5 ml of DMSO-d 6/CDCl 3 while for 13C NMR spectra, about 50 mg of the compound was dissolved in the same volume of the solvent. Tetramethylsilane (TMS) was used as an internal standard and the chemical shift value ( ) are given in parts per million (ppm). High resolution mass spectra using JEOL GCMATE II/ VARIAN SATURN 2200 GC-MS spectrometer were also recorded for the further confirmation of the synthesized compounds. 2.7. SINGLE CRYSTAL XRD ANALYSIS Suitable crystals of the reported compound were obtained by the slow evaporation technique in ethanol solvent medium. The selected crystal data and data collection parameter of the compound
36 were collected on a BRUKER AXS KAPPA APEX-II diffractometer using graphite-monochromated Mo (K ) radiation and ( = 0.71073 Å) at 293 K with crystal size 0.20 0.20 0.30 mm. The structure was solved by direct methods and successive Fourier difference syntheses (SHELXS-97) 171 and refined by full matrix least square procedure on F 2 with anisotropic thermal parameters. All non-hydrogen atoms were refined (SHELXL-97) 172 and placed at chemically acceptable positions. Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre. 2.8. COMPUTATIONAL ANALYSIS Computational calculations of the selected compounds were performed using Gauss View molecular visualized program 173 and Gaussian 03W package 174 on the personal computer [Processor (Intel(R) Core(TM)2 Duo CPU E7200 @ 2.53 DHz)]. The molecular structures of the thiazolyl hydrazones in the ground state were optimized by density functional theory (DFT) using B3LYP/6-311G(d,p) level. 83,84 The geometrical parameters (bond length, bond angle, dihedral angle), Frontier molecular energies (E HOMO, E LUMO and their energy gap, E), molecular electrostatic potential (MEP) distribution and natural bonding orbital (NBO) analysis of all molecules were obtained from the optimized structures. The obtained favoured optimize geometry, molecular orbital and electrostatic potential diagram of the all molecules were visualized from Gauss View molecular visualized program.
37 2.9. ANTIMICROBIAL STUDIES 2.9.1. Antibacterial studies The synthesized derivatives were screened for their antibacterial activity against three Gram-positive bacteria viz., Streptococcus pyogenes, Bacillus subtilis and Staphylococcus aureus and two Gram-negative bacteria viz., Escherichia coli and Pseudomonas aeruginosa using the disc diffusion method. 175-177 Ciprofloxacin/Ampicillin were used as reference standard for comparing the results. 2.9.1.1. Culture medium Nutrient broth was used for the preparation of inoculum of the bacteria and nutrient agar was used for the screening method. Composition of Nutrient agar medium Peptone : 5.0 g Sodium chloride : 5.0 g Beef extract : 1.5 g Yeast extract : 1.5 g Agar : 15.0 g Distilled water : 1000 ml ph : 7.4 ± 0.2
38 2.9.1.2. Determination of antibacterial activity by disc-diffusion method The test organisms were subcultured using nutrient agar medium. The tubes containing sterilized medium were inoculated with the respective bacterial strain. After incubation at 37ºC ±1ºC for 18 hrs, they were stored in a refrigerator. The nutrient agar medium was sterilized by autoclaving at 121ºC for 15 min. The petriplates, tubes and flasks plugged with cotton were sterilized in hot-air oven at 160ºC, for an hour. Into each sterilized petriplate (20 cm diameter), was poured about 125 ml of molten nutrient agar medium which was already inoculated with the respective strain of bacteria (5 ml of inoculums to 250 ml of nutrient agar medium) aseptically. The plates were left at room temperature aseptically to allow the solidification. After solidification, the paper discs containing the derivatives were placed at different areas on the surface of each plate and labelled accordingly. 2.9.1.3. Preparation of solution of test compounds Each test compound (5 mg) was dissolved in dimethyl sulfoxide (DMSO, 5 ml AR grade) to give a concentration of 1000 µg ml -1. Ciprofloxacin/Ampicillin solution was also prepared to give a concentration of 1000 µg ml -1 in sterilized distilled water. The ph of all the test solutions and control was maintained in between 2 to 3 by using conc. HCl. All the compounds were tested at dose levels of 1000 µg and DMSO used as a control. The solutions of each test compound, control
39 and reference standard were added separately in the cups and the plates were kept undisturbed for at least 2 h in a refrigerator to allow diffusion of the solution properly into nutrient agar medium. Petridishes were subsequently incubated at 37 ± 1 C for 24 hrs. After incubation, the diameter of zone of inhibition surrounding each of the cups was measured with the help of an antibiotic zone reader. 2.9.2. Antifungal studies All those compounds screened earlier for antibacterial activity were also tested for their antifungal activity. The fungi employed for the screening were Aspergillus flavus, Aspergillus niger, Penicillium chrysogenum, Trichoderma viride and Fusarium oxysporum. Amphotericin-B was employed as standard to compare the results. The test organisms were subcultured using Potato Dextrose Agar (PDA) medium 150,151. The tubes containing sterilized medium were inoculated with test fungi and kept at room temperature for obtaining growth. After that, they were stored at 4ºC in a refrigerator. Composition of Potato-Dextrose-Agar medium Peeled potato : 50.0 gm Dextrose Agar Distilled water : 5.0 gm : 4.0 gm : Up to 200 ml
40 The test organisms were subcultured using PDA medium. The tubes containing sterilized medium were inoculated with respective fungal strain and kept aside at room temperature for growing the organism. After confirming the growth, they were stored in a refrigerator. The inoculum was prepared by aseptically transferring 10 ml of sterile water into freshly sub-cultured slants of the test fungi and making a suspension by scraping the growth with an inoculation medium. The PDA medium was sterilized by autoclaving at 121ºC for 15 min. The petri-plates, tubes and flasks plugged with cotton, were sterilized in hot-air oven at 160ºC, for an hour. Into each sterilized petri-plate (20 cm diameter), poured about 125 ml of molten PDA medium which was already inoculated with the respective strain of fungi (5 ml of inoculums to 250 ml of nutrient agar medium) aseptically. The plates were left at room temperature aseptically to allow the solidification. After solidification, the paper discs containing synthesized derivatives were placed at different areas on the surface of each plate and labelled accordingly. 2.9.2.1. Preparation of test compounds Each test compound (5 mg) was dissolved in DMSO (5 ml, AR grade) to give a concentration of 1000 µg ml -1. Amphotericin-B solution was also prepared at a concentration of 1000 µg ml -1 in sterilized distilled water. The ph of all the test solutions and control
41 was maintained at 2 to 3 using conc. HCl. All the compounds were tested at dose levels of 200 µg (0.2 ml) and DMSO used as a control. The solutions of each test compound, control and reference standards were added separately in the cups and the plates were kept undisturbed for at least 2 hrs in a refrigerator to allow diffusion of the solution properly into the PDA medium. Petri-dishes were subsequently kept at room temperature for 48 hrs. After that, the diameter of zone of inhibition in mm surrounding each of the cups was measured with the help of an antibiotic zone reader.