Synthesis and Characterization of Some Heterocyclic Compounds and Evaluation of Antibacterial Activity

In this study, heterocyclic compounds with two nitrogen atoms are prepared by reaction of 2-aminobenzimidazole with formic acid to get amide derivatives (A), reacts with phenylhydrazine to get phenyl hydrazone derivatives (B), reacts with ethyl chloroacetate to obtain ethyl acetate derivatives (C). The derivative (D) obtains on heating in a basic medium. The (B) reacts with 2-chloroacetyl chloride to give derivatives (E). A number of Schiff bases are prepared (F, I) from reacting 2-aminobenzimidazole with benzaldehyde derivatives. The(F) reacts with propargyl bromide to give propargyl bromide derivatives (G). The cyclization with 4-nitrophenyl azide leads to obtain triazole compound (H). The compound (I) reacts with ethyl chloroacetate to give ethyl acetate derivatives (J), reacts with hydrazine to give N-amide hydrazine derivatives (K). The cyclization give rises to 1,3,4-oxadiazole derivatives (L). The compound (I) reacts with sodium azide to obtain tetrazole derivatives (M). Synthesizing of Triazine, Oxadiazole, Triazole, Tetrazole via cyclization of the Schiff base derivatives with ethyl chloroacetate and chloro acetyl chloride, benzoic acid, 4-nitrophenyl azide, sodium azide and phenyl azide are possible respectively. The FT-IR, C-NMR and H-NMR spectral data give good evidence for the formation of the compounds. Someprepared compounds exhibit antibacterial properties.

Heterocyclic compounds, 2-aminobenzimidazole, Triazine, Triazole, Oxadiazole, Tetrazole, Schiff base, Therapeutic use A In this study, heterocyclic compounds with two nitrogen atoms are prepared by reaction of 2-aminobenzimidazole with formic acid to get amide derivatives (A), reacts with phenylhydrazine to get phenyl hydrazone derivatives (B), reacts with ethyl chloroacetate to obtain ethyl acetate derivatives (C). The derivative (D) obtains on heating in a basic medium. The (B) reacts with 2-chloroacetyl chloride to give derivatives (E). A number of Schiff bases are prepared (F, I) from reacting 2-aminobenzimidazole with benzaldehyde derivatives. The(F) reacts with propargyl bromide to give propargyl bromide derivatives (G). The cyclization with 4-nitrophenyl azide leads to obtain triazole compound (H). The compound (I) reacts with ethyl chloroacetate to give ethyl acetate derivatives (J), reacts with hydrazine to give N-amide hydrazine derivatives (K). The cyclization give rises to 1,3,4-oxadiazole derivatives (L). The compound (I) reacts with sodium azide to obtain tetrazole derivatives (M). Synthesizing of Triazine, Oxadiazole, Triazole, Tetrazole via cyclization of the Schiff base derivatives with ethyl chloroacetate and chloro acetyl chloride, benzoic acid, 4-nitrophenyl azide, sodium azide and phenyl azide are possible respectively. The FT-IR, 13 C-NMR and 1 H-NMR spectral data give good evidence for the formation of the compounds. Some prepared compounds exhibit antibacterial properties.

Heterocyclic compound
Heterocycles are cyclic compounds in which the ring contains atoms other than carbon and hydrogen, i.e. some other elements, such as nitrogen, sulfur or oxygen, it is called the hetero-atom (Bahl and Bahl, 2008;lvaez Builla and Barluenga, 2011). They show relative stability and aromaticity (Tewari and Vishnoi, 2017). The heteroatom types in the ring structure can categorize the heterocycles into oxygen, nitrogen or sulfur base. The compounds are subclassi ied also according to the ring structure size that in turn ascertain by whole atoms number. Its physiochemical properties correlate strongly with type and size of the ring structure as well as the substituent groups of the core scaffold (Martins et al., 2015). The heterocyclic compounds constitute a signi icant percent of the organic compounds and have an important role in biological and medical systems (Gupta, 2015). Triazine, triazole, oxadiazole and tetrazole are examples of heterocyclic compounds that implicated in this study.

Triazine
S-triazine or 1,3,5-triazine is a six-membered ring containing three carbons replaced by nitro-gen joined by alternating single and double bonds (Smolin and Rapoport, 1959). It has a variety of industrial and biological applications in herbicides, polymer photostabilization and antitumor therapy (Sarmah et al., 2012). New s-triazine derivatives have also implicated as anti-AIDS, antituberculosis, and anticancerous (Baldaniya and Patel, 2009).

Oxadiazole
Oxadiazole is a ive-membered ring compound with an oxygen atom and two atoms of nitrogen and carbon (Sanchit, 2011;Mousa and Jassim, 2018). The general formula of this compound is C 2 H 2 ON 2 .

Tetrazole
Tetrazole is a ive-membered heterocyclic compound that its ring contains a carbon atom and four nitrogen atoms (Wei et al., 2015).
The tetrazole moiety has a wide number of applications and its nitrogen-rich ring system is used in explosives, propellants and pharmaceuticals (Shanmugam et al., 2013). So, they have reported as antiallergic and anti-asthmatic, anti-neoplastic, antiin lammatory, antiviral and anticognitive disorder activities (Zamani et al., 2015).

Aim of the study
This study aims to synthesize new heterocyclic compounds derived from benzimidazole containing triazine, triazole, tetrazole and oxadiazole moiety and study the antibacterial activity for some selected prepared compounds. (Petrova et al., 2015) A 2-aminobenzimidazole (0.5 g, 0.003 mol) and formic acid was re luxed in water bath for 13 hours. TLC was used to monitor the reaction course. Then, formic acid excess was evaporated and recrystallized the product from appropriate solvent to get a beige product, (0.47 g, 79%). IR: 1610IR: , 1327IR: , 1566IR: , 1681IR: , 3045, 2824 (Sayed et al., 2018) A (0.3 g, 0.001 mol) of the compound (B) was dissolved in 15ml of ethanol with some drops of triethylamime. Then, (0.14 g, 0.001 mol) ethyl chloroacetate was added, stirring in a water bath at 67 o C for 2 hours and TLC monitored the progression. The compound was puri ied by recrystallization from ethanol, light brown crystals were obtained, (0.34 g, 85%). IR: 1592IR: , 1035IR: , 1487IR: , 1742IR: , 2971IR: , 1306IR: , 1182 cm −1 , as shown in Scheme 3. (Dolzhenko, 2011) A mixture of (0.3 g, 0.0008 mol) of the compound (C) and few KOH drops solution in ethanol 10% in solvent ethanol was stirred for 10 minutes at room temperature. Then, it was subjected to re lux for 45 hours. The TLC told there was no starting materials left, the solvent was allowed to evaporate slowly to get a brown product, (0.22 g, 84%). IR: 1493, 1378, 1551, 1731, 2977,1196 cm −1 , as shown in Scheme 4. (Soleiman et al., 2016) A (0.3 g, 0.001 mol) of the compound (B) was dissolved in ethanol with some drops triethylamine and stirred more than 5 minutes. Then, (0.13 g, 0.001 mol) of chloro acetyl chloride was added slowly to the reaction solution and stirred in an ice bath during addition. The stirring in a water bath was at 67 o C for 3 hours. TLC followed the progress, and the compound was puri ied by recrystallization from ethanol to get a golden beige crystals, (0.27 g, 80%), as shown in Scheme 5.
(L) Synthesis of 1-(4-chlorophenyl)-N-(1-((5phenyl-1, 3, 4-oxadiazol-2-yl) methyl)-1Hbenzo[d]imidazol-2-yl) methanimine (Hameed and Akhtar, 2011) A (0.18 g, 0.0005 mol) of the compound (K) was dissolved with (0.06 g, 0.0005 mol) benzoic acid using 10 ml of POCl 3 as a solvent. This mixture gently re luxed for 36 hours. Then, crushed ice was added slowly. The mixture was mixed slowly with continuous stirring. The acid mixture was mixed with potassium carbonate. TLC was used to follow the reaction progress. Then, it was left for the next day to settle down, collected the precipitate by iltration and washed with distilled water (50 ml). The product was dried to get a beige powder (

(M) Synthesis of 2-(5-(4-chlorophenyl)-4,5dihydro-1H-tetrazol-1-yl)-1H-benzo[d]imidazole
A (0.17 g, 0.0006 mol) of the compound (I) was dissolved in THF. Then, (0.039 g, 0.0006 mol) of sodium azide was added to this solution, stirring in a water bath at 67 o C for more than 10 hours. The progression was followed by usage of TLC. The product was dried to obtain an orange powder, (0.13 g, 70%), as shown in Scheme 13. Table 1 delineates the physical properties for these compounds.

Antibacterial activity assay
Biologically, the antibacterial activity for three selected synthesized derivatives, viz. compounds L, M and D, were evaluated using two aerobic bacteria that isolated from infected burn wounds: Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) as an example for Gram-positive andnegative bacteria respectively. Agar well diffusion method (Aljanaby, 2018) was applied to assess that activity. The synthesized derivative compounds dissolved in Dimethyl Sulphoxide (DMSO) to prepare three samples (25, 50 and 75 mg/ml) from each. Then, four wells have made in Muller-Hinton Agar by sterile(5mm) borer. Suspension of the tested bac-teria (1x10 6 CFU/ml) was spread on media plates by sterile cotton swabs. 100 µl from each concentration was transferred to each well and left at the room temperature for 15 minutes to allow the compound to spread into the agar and incubated at 37 • C for 24 hours. The tests were conducted in triplicate. The diameters of inhibition zones that arose out were measured in millimeters (mm).

Statistical analysis
IBM SPSS statistics, version 8 for windows, was the statistical software that have been used for the analysis to make comparisons between inhibition zones diameters (mm). T-test had implicated and P-value < 0.05 was considered to be statistically signi icance.

Antibacterial activity
The estimated antibacterial activity for derivative compounds (L, M and D), based on diameters of its own inhibition zones, gives "good" effect against pathogenic bacteria with signi icant inhibition zone appeared at every concentration (25, 50 and 75 mg/ml), (Table 2 and Figure 1). The (M) compound gives "excellent" effect against E. coli at concentrations of 50 and 75 mg/ml, inhibition zone diameters 21.667 ± 0.88192 and 25.333 ± 0.33333 mm respectively; however, the inhibition zone diameters are 20.667 ± 0.66667 and 25.000 ± 0.57735 respectively against S. aureus (Aljanaby, 2018).

CONCLUSIONS
Heterocyclic amine derivatives can be used as reagents for elements. The 2-aminobenzimidazole can be used as a launching material to synthesize number of compounds (Triazine, Oxadiazole, Triazole and Tetrazole). Synthesizing of Triazine, Oxadiazole, Triazole, Tetrazole via cyclization of the Schiff base derivatives with ethyl chloroacetate and chloro acetyl chloride, benzoic acid, 4-nitrophenyl azide, sodium azide and phenyl azide are possible respectively. The FT-IR, 13 C-NMR and 1 H-NMR spectra data give good evidence for the formation of the compounds that have been prepared. Some of prepared compounds exhibit antibacterial agents.