Synthesis and Biological Evaluation of Some New 1,2,3-Triazole Derivatives As Anti-microbial Agents

A series of 1,2,3-triazole derivatives bearing different chemical entities were prepared starting from 2-(4-phenyl1H-1,2,3-triazol-1-yl)acetohydrazide, compound 2. The purity of all new compounds was checked by TLC and elucidation of their structures was confirmed by IR, 1 H and 13 C NMR along with High Resolution Mass Spectrometry (HRMS). All the target compounds were evaluated for their possible antimicrobial activity. Most of the tested compounds showed moderate to good antibacterial activity against most of the bacterial strains used in comparison with ciprofloxacin as a reference drug. The most active compounds were 4a, 9a, 9b, and 9f. Results of antifungal activity revealed that most of the tested compounds showed a good antifungal activity in comparison to fluconazole as a reference drug. Compounds 4a, 9c, 9d and 9f were the most active ones.

Morbidity and mortality due to enteric bacterial infections have caused important health problems worldwide, mainly in the developing countries [15][16]. Toxicity and resistance to the drugs also have played an important role in treatment failure [17]. Consequently, there is an urgent need to screen new compounds for the development of new antibacterial agents.
We report simple and efficient methods for preparation of 1,2,3-triazole derivatives bearing different chemical entities that promise superior antimicrobial activity.

Chemistry
The key intermediate ethyl 2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetate, compound 1 was prepared according to a reported procedure and its structure was confirmed by matching its physical and spectral data with the reported one [18].
The novel 2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetohydrazide, compound 2 was obtained through condensation of compound 1 with hydrazine hydrate by heating the reactants in ethanol at reflux for 6h, Scheme 1. IR spectrum of compound 2 showed two bands at 3290 and 3160 cm -1 due to NH and NH2 functions, in addition to a band at 1658 corresponding to carbonyl group.
Hydrazide 2 was allowed to react with phthalic anhydride in glacial acetic acid by heating the reactants at reflux for 2 h to afford the new phthalimide derivative 3 in a 78% yield, Scheme 1. IR spectrum of compound 3 showed one band at 3260 cm -1 due to (-NH) stretching and two bands at 1699 and 1648 for carbonyl groups. 1 H NMR spectrum of compound 3 displayed no signals belonging to -NH2 group. HRMS of compound 3: Found 348.1087, Calculated for (C18H14N5O3 The novel thiosemicarbazide derivatives 4a-c were obtained in 76-84% yields through the reaction of acid hydrazide 2 with the appropriate isothiocyanate by heating the reactants at reflux in ethanol for 2 h. Furthermore, the thiosemicarbazides 4a-c were cyclized in hot NaOH solution as a base catalyzed reaction to obtain the novel 5mercapto-4-substituted-4H-1,2,4-triazole derivatives 5a-c. The IR spectra of compounds 4a-c showed strong absorption bands at 3265-3234 cm -1 and 1666-1652 cm -1 for the NH and C=O groups, respectively. In addition to a strong absorption band at 1190 cm-1 due to (C=S) group. Meanwhile IR spectra of compounds 5a-c displayed no bands belonging to NH and C=O groups; instead a new bands at 2988-2962 cm -1 for SH group. J a n u a r y 1 7 , 2 0 1 5 Scheme 1 Synthesis of compounds 2, 3, 4a-c, and 5a-c Moreover, the novel oxadiazole 6 was synthesized in 87% yield through cyclization of the acid hydrazide 2 using potassium hydroxide and carbon disulfide in hot ethanolic solution. IR spectrum of compound 6 showed a band at 2961 cm -1 due to SH group. HRMS of compound 6: Found 260.0594, Calculated for (C11H10N5OS + ) 260.0601.
The intermediate potassium 2-(2-(4-phenyl-1H-1,2,3-triazol-1-yl)acetyl)hydrazine carbodithioate 7 was prepared from hydrazide 2 and carbon disulfide in ethanolic potassium hydroxide solution with the aim to be cyclized to the novel triazole 8 under the effect of hydrazine hydrate. Structure of compound 8 was elucidated by spectral methods of analyses. IR spectrum of compound 8 showed two bands at 3270 and 3135 cm -1 due to (NH) stretching, a band at 2720 cm -1 for SH group and a strong band at 1299 cm -1 (C=S) stretching (thiol-thionetautomers). IR spectrum of compound 8 was devoid of absorption bands around 1660 cm -1 due to carbonyl group of hydrazide. 1 H NMR spectrum of compound 8 displayed no signalsbelonging to -NH2 and -CONH groups; instead, a new singlet signal appeared at 5.68 ppm (exchangeable with D2O) due to -NH2 of triazole ring equivalent to two protons and a broad signal at 13.85 ppm due to exchanged -NH proton of triazole ring. HRMS of compound 8: Found 274.0867, Calculated for (C11H12N7S The target compounds; 9a-f were synthesized by condensation of compound 2 with (un)substituted benzaldehydes or acetophenone Scheme 2. The structures of compounds 9a-f were confirmed by spectral methods of analyses. The IR spectra of compounds 9a-f showed strong absorption bands at 3255-3160 cm -1 and 1680-1668 cm -1 for the NH and C=O groups, respectively. J a n u a r y 1 7 , 2 0 1 5

Biology
The results of the preliminary testing of the antibacterial activity of the final compounds are given in Table II. The synthesized compounds 2, 3, 4a-c, 5a-c, 6, 8, and 9a-f were tested for their in vitro antibacterial activity against Staphylococcus aureusas a representative of Gram positive strains and Escherichia coli as a Gram negative strain using ciprofloxacin as a reference drug. The result revealed that most of the newly synthesized compounds exhibited promising antibacterial activity comparable to ciprofloxacin against the test organisms (Table II).
The hydrazide derivative compound 2, was found to exhibit antibacterial activity nearly 48% that of ciprofloxacin against Staphylococcus aureus, however it showed only 40% activity of ciprofloxacin against E.Coli.
According to the results in Table II, it can be noticed that conversion of hydrazide derivative, compound 2 into compound 3 decreased the activity against Staphylococcus aureus as it showed only 38% activity of ciprofloxacin.
Compounds 4a-c were found to exhibit pronounced antibacterial activity which ranged from 60-73% that of standard drug against Staphylococcus aureus and 45-60% that of ciprofloxacin against E.Coli. It is worthy-mentioning that compound 4a showed the highest activity (73%) against Staphylococcus aureus and 60% activity of ciprofloxacin against E.Coli. J a n u a r y 1 7 , 2 0 1 5 Furthermore, compounds 5a-c exhibited moderate activity against Staphylococcus aureusand their activity was 53-60% that of ciprofloxacin, but they showed weak activity (45-47% that of ciprofloxacin) against E.Coli and that compound 5a was the most active compound against Staphylococcus aureusas it showed 60% that of ciprofloxacin while it showed only 47% activity against E.Coli. It was noticed that cyclization of thiosemicarbazides 4a-c to their corresponding triazole derivatives 5a-c led to decrease of the antibacterial activity.
The oxadiazole derivative, compound 6 showed moderate activity against Staphylococcus aureusand its activity was 68% that of ciprofloxacin while it showed only 55% activity of ciprofloxacin against E.Coli. Meanwhile, the conversion of hydrazide 2 into the amino triazole derivative, compound 8 did not show a significant improvement in the antibacterial characters of compound 2.
Compounds 9a-f were found to exhibit pronounced antibacterial activity which ranged from 65-85% that of standard drug against Staphylococcus aureus and 50-80% that of ciprofloxacin against E.Coli. It is worthy-mentioning that compound 9f showed the highestactivity (85%) against Staphylococcus aureus while compound 9d was the most active derivative against E.Coli(80% avtivity).
The results revealed that the tested compounds showed a varying degree of antifungal activity against the test organism. Compound 2 showed activity 40% that of fluconazole. Moreover, further derivatization of compound 2 with different (un)substituted benzaldehydes and acetophenone, compounds 9a-f affords compounds with improved antifungal activity against Candida albicans, showing activity 50-80% that of fluconazole. Compound 9e displayed the higher antifungal activity among the other derivatives as it showed 80% activity of fluconazole. J a n u a r y 1 7 , 2 0 1 5

CONCLUSION
In conclusion, several 1,2,3-triazole derivatives bearing different chemical entities were synthesized. A microbiological study was undertaken to evaluate the effect of the synthesized compounds on different bacterial and fungal strains. The results of the preliminary testing of the antibacterial activity of the final compounds revealed that the majority of the synthesized compounds show varying degrees of inhibition against the tested microorganisms. In general, the inhibitory activity against the Gram-positive bacteria was higher than against the Gram-negative bacteria. The triazole derivatives 4a, 9a, 9b, and 9f, displayed the highest activity. Results of antifungal activity revealed that all compounds showed a weak to a good antifungal activity and that compounds 9c, 9d, 9e and 9f were the most active ones.
Melting points were determined on an electro thermal melting point apparatus [Stuart Scientific, model SMP3, England, UK], and were uncorrected. Pre-coated silica gel plates (kieselgel 0.25 mm, 60G F254, Merck, Germany) were used for TLC monitoring of reactions. The developing solvent systems of CHCl3/CH3OH (9.5:0.5 V/V) were used and the spots were detected at 254 nm wavelength using ultraviolet lamp (Spectroline, model CM-10, USA). The target compounds were crystallized from ethanol unless otherwise specified. IR spectra (KBr discs) were recorded on a shimadzu IR-470 spectrometer (Shimadzu, Kyoto, Japan) at Faculty of Pharmacy, Assiut University, Assiut. NMR Spectra were taken using a Varian Unity INOVA 400 MHz and Bruker AC250 MHz spectrometers for proton and carbon. All numbers referring to NMR data obtainedare in parts per million (ppm) relative to TMS as an internal standard, using DMSO-d6, unless otherwise specified, as a solvent, and deuterium oxide was used for the detection of exchangeable protons.. High resolution mass spectrometric data were obtained using the EPSRC mass spectrometry centre in Swansea and Thermo Instruments MS system (LTQ XL/LTQ Orbitrap Discovery) coupled to a Thermo Instruments HPLC system (Accela PDA detector, Accela PDA autosampler and Pump) at university of Aberdeen.

Antibacterial screening Organisms and culture conditions
The used bacterial cultures were obtained from Assiut University Mycological Center (AUMC), Assiut University. The synthesized compounds (2, 3, 4a-c, 5a-c, 6, 8, and 9a-f) were tested for their in-vitro antibacterial activity in comparison to ciprofloxacin as a reference drug using the standard agar cup diffusion method [19] against Staphylococcus aureus(AUMC B54) as a representative of Gram positive strains, while the Gram negative strains were represented by Escherichia coli (AUMC B69).

Materials and method
Bacterial strains were individually cultured for 48 h in 100 mL conical flasks containing 30 mL Nutrient Agar (NA). Assay was done in 10 cm sterile Petri dishes in which one mL bacterial suspension and 15 mL of NA were poured. Plates were shaken gently to homogenize the inocula. After solidification of the media, 5 mm cavities were cut in the solidified agar (4 cavities/plate) using sterile cork borer. The test compounds (2, 3, 4a-c, 5a-c, 6, 8, and 9a-f) and ciprofloxacin were dissolved in dimethyl sulfoxide (100 μmol/mL) and were pipeted in the cavities. In addition, other cavities were pipeted with the solvent (DMSO) and served as a negative control. The seeded plates were incubated at 28 ± 2°C for 48 h.
The radii of inhibition zones (in mm) of triplicate sets were measured and the results are cited in table II.