Design and Synthesis of Some New Derivatives of Chlorobenzyl-Oxy-Phenyl-Ethyl-Thio-1H-Tetrazole and Study Their Antibacterial and Antifungal Activity

In recent years tetrazole scaffolds have been attracted interest in the field of synthetic and medicinal chemistry research. The unique structure of the tetrazole derivatives exhibits widespread applications in biology and technology. The close structural resemblance with carboxylic acid acts as a booster of the latter. Due to this diversified potential utilization, several methods are reported for the synthesis of tetrazole scaffolds. Here in this chapter, we describe the synthesis of chlorobenzyl-oxy-phenyl-ethyl-thio-1H-tetrazole derivatives ( 6a-p ). The newly synthesized derivatives are characterized by spectral characterization and screened for their antifungal activity. Among these, some of the newly synthesized compounds show potent antifungal activity.

effects, high toxicity, and narrow antimicrobial spectrum which are unresolved. Literature in recent years endorsed that, the total number of publications on the chemistry of N-containing heterocycles consequential boost to discover the new drugs and assuring their biological activity which mainly contains tetrazole moiety.
Tetrazole is an important heterocyclic scaffold containing nitrogen. It is a unique nitrogen-rich compound among the known stable heterocycles and in spite not found in nature [4]. In 1885, for the first time synthesized and characterized compound embedding a tetrazole ring, is 2-phenyl-2H-tetrazole-5-carbonitrile [5]. Tetrazole is a remarkable synthetic scaffold that noticed wide applications in various fields like in medicinal, pharmacological, biochemistry, and in industrial [6][7][8][9][10].
Besides this, tetrazole has noticed a broad spectrum of applications in materials like information recording systems [40], rocket propellants [41][42], specialty explosives [43], and agrochemical applications [44][45][46][47]. As befitting coordination property, it has also capable to form nitrogen containing ligands and designing stable complex with disparate metal ions and react as precursors to varied nitrogen containing heterocyclic compounds in organic synthesis [48]. Thus, the whispered applications of tetrazole skeleton in numerous fields make interest for the development of novel tetrazole derivatives. Some of them are displayed in Fig. 1.1. By studying the above literature data and as a part of our research to design and synthesis bioactive heterocyclic compounds [49][50][51][52][53], in the present work, our strategy is to synthesize tetrazole embedded novel derivatives and study their antibacterial and antifungal activity.

Chemistry
The synthetic pathway of the target compound chlorobenzyl-oxy-phenyl-ethyl-thio-1Htetrazole derivatives (6a-p) is summarized in Further, the C=O bond of the compound (3a-h) undergoes reduction by Sodium borohydride (NaBH 4 ) in PEG-400 at room temperature to yield the next intermediate products (4a-h). Then compounds (4a-h) were to couple with chlorobenzyl chloride (5a-b) by using catalytic amount BEC in PEG-400 to give the targeted compound chlorobenzyl-oxy-phenyl-ethyl-thio-1Htetrazole derivatives (6a-p) in admirable yields (Scheme 2).

Scheme 2. Variation of substituent on tetrazole (6a-p)
To achieve the target compounds (6a-p), here we reported an eco-friendly synthetic route which accomplishes by using BEC (pH 12.5) as a heterogeneous catalyst to attain the basic media in PEG-600 as a green reaction solvent.
Finally, the structures of the synthesized products were determined by IR, 1 H NMR, 13

Antibacterial Activity:
Regarding the antibacterial activity, the results revealed that the newly synthesized compounds displayed variable inhibitory effects on the growth of the tested Gram positive and Gram negative bacterial strains. Some of the synthesized compounds showed relatively high sensitivity against Gram positive bacterial strains namely; S. aureus and B. subtilis. In this view, compound 6l was equipotent to ciprofloxacin (MIC 3.12g/mL) against S.aureus, whereas the analogs 6e, and 6m (MIC 6.25g/mL) were 50% less active than ciprofloxacin. Moreover, compound 6k (MIC 12.5g/mL) showed 25% of the activity of ciprofloxacin against the same organism. Concerning the activity against B. subtilis, the best activity was displayed by compound 6l (MIC 6.25g/mL), which represented half the potency of ciprofloxacin. On the other side, analog 6d, 6e, 6k, and 6m (MIC 12.25g/mL) exhibited 25% of the potency then ciprofloxacin against the same species. On the other hand, investigation of antibacterial activity of the active compounds against the three tested Gram negative strains revealed that two analogs namely 6d and 6l were able to produce moderate growth inhibitory activity against E. coli (MIC 6.25g/mL) which was 25% of the activity of ciprofloxacin. Whereas, compounds 6e and 6m, (MIC 12.5g/mL), exhibited moderate activity against the same organism. Meanwhile, the activity against P. aeruginosa, compound 6d, 6e, 6l, and 6m (MIC 12.5g/mL) exhibited 50% potency as compared to ciprofloxacin. The reaming synthesized compounds were proved to be weakly sensitive against the examined strains. The screening result was exhibited in

General procedure for the synthesis of 1-(substituted phenyl)-2-thiocynatoethanone (2a-h)
A mixture of potassium thiocynate (1.00 mm) and substituted phenacyl bromide (1.00 mm) in PEG-400 was stirred continuously for 1-2 hrs at 60-70°C. Progress of the reaction was monitored by TLC and the product was separated from the crude reaction mixture in ice cold water. The separated solid was filtered simply, dried and recrystallized in aq. acetic acid to afford the pure product.

General procedure for the synthesis of 2-((1H-tetrazol-5-yl)thio)-1-(substituted phenyl)ethanone (3a-h)
Compounds 2a-h (1.00 mm) and sodium azide (1.00 mm) were taken in PEG-400 with a catalytic amount of TBAB. This reaction mixture was stirred at 70-80°C for 1-2 hrs. The reaction was monitored by TLC. After completion of the reaction, the reaction mixture was poured in ice cold water to isolate the solid product. The solid products were collected by simple filtration method, dried and recrystallized in aq. acetic acid.

General procedure for the synthesis of 2-((1H-tetrazol-5-yl)thio)-1-substitutedphenylethanol (4a-h)
Compounds 3a-h (1.00 mm) in PEG-400 was stirred at room temperature in presence of a catalytic amount of sodium borohydrate (0.25 mm) for 30 min. After completion of the reaction (monitored by TLC), the reaction mixture stands for 1hr at room temperature and is poured in ice cold water. The separated product was filtered, dried wash with water and recrystallized from aq. acetic acid.

-((2-((4-chlorobenzyl)oxy)-2-(4chlorophenyl)ethyl)thio)-1H-tetrazole (6a-p)
An equimolar mixture of compounds 4a-h (1.00 mmole) and substituted chlobenzylchloride (1.00 mmole) were stirred continuously in presence of a catalytic amount of Bleaching Earth Clay (pH-12.5, 10 wt %) as a heterogeneous catalyst to attain basic media in PEG-400 for 1 hr at 70-80ºC. After completion of reaction monitored by TLC the reaction mixture was cooled at room temperature and worked up with ice cold water. After filtration the separated product was washed with hot water, dried and recrystallized from aq. acetic acid to obtain a pure final product.

Biology
All the newly synthesized target compounds (6a-p) were evaluated for their in vitro antibacterial and antifungal activities at 100µg/mL concentration against Staphylococcus aureus (MTCC), screening. The results of biological screening against the standard strains are recorded in Fig. 1 and Fig. 2 which manifestly depicted the distinct sense of antibacterial and fungal strains toward the tested compounds.