INTRODUCTION:

Microwave dielectric heating uses the ability of some liquids and solids to transform electromagnetic radiation into heat to drive chemical reactions. The entry of microwave ovens possible to carry out many transformations with greater efficiency and ease of workup ^(1-3), the use of microwave has becomes very attractive in the field of medical sciences ⁽⁴⁾.

Bicyclic aromatic heterocycles containing nitrogen benzimidazole is ubiquitous in pharmaceuticals and natural products and many of them exhibit unique biological activities. The benzimidazole is a crucial heterocyclic skeleton often associated with biological activity. A number of derivatives of Benzimidazoles are known to possess potent pharmacological activity including anti-inflammatory, anti-tumor or HIV protease inhibition^(5,6) and inhibition of protein kinase inhibitors.⁽⁷⁾

In fact, compounds containing the benzimidazole skeleton are known to show a variety of biological activities such as high binding affinity for estrogen receptor⁽⁸⁾ antifungal, antibacterial activity⁽⁹⁾Among the important heterocycles, many of the natural and synthetic benzimidazole –based heterocycles with diverse mechanism of action have been reported as lead anticancer⁽¹⁰⁾ 5-HT2, 5-HT3 and 5-HT4 receptor antagonisms^(11-13) It has been screened of antibacterial activity against staphylococcus and E.coli.

The chemistry of Schiff base plays a vital role in the progress of chemistry science ^(14,15), synthesis of Schiff base through classical condensation of aldehydes (or ketone) and imines were pursued ^(16,17) Schiff base are characterized by the N=CH- (imine) group which is important in elucidating the mechanism of transformation in biological systems. Due to great flexibility and diverse structural aspects, wide range of Schiff bases have been synthesized and their complexion behavior was studied ⁽¹⁸⁾. Furthermore, Schiff base are reported to show a variety of interesting biological activities, including antibacterial ⁽¹⁹⁾, antifungal ⁽²⁰⁾, anticancer ^(21,22), and herbicidal activities ⁽²³⁾. 2-Azetidinone and Thaizolidinone compounds are characterized by the ring system ⁽²⁴⁾. These compounds are shown to possess make biological activities ^(25-29). 2-Azetidinone and Thaizolidinone has been synthesized by the condensation of chloroacetyl chloride and mercpto acetic acid respectively with Schiff base, this compound has been characterized on the base of analytical and spectral data.

EXPERIMENTAL WORK:

Melting point were determined in Buchi thermal point apparatus and were uncorrected, Elemental analysis (CHN) were recorded in EA300 Euro-Vector in University of Al-albyat in Jordon. FT-IR Spectra were recorded on Shimadzu FT-IR 8400 Fourier Transformer infrared as KBr disk in the range 40-4000 cm^-1. Ultraviolet spectra were recorded in spectro scan 80 in the wavelength 200-800 nm. ¹HNMR and ¹³CNMR spectra were recorded on Bruker spctrospin ultra shield magnets 400MHz instrument using tetramethylsilane (TMS) as an internal standard and DMSO-d⁶ as a solvent in university of Tabriz-Iran. The compounds were synthesized by microwave type Newal microwave instrument (Turkey) NWL101, compact 20L, power1200 Watt and frequency 2450 MHz, by using turntable system with different powers between 90-300W. Thin layer chromatography were performed on pre-coated sheets with 0.25 mm layer of Silica Gel GF254 of the Merck Company.

1- Synthesis of benzimidazole

A mixture of o-pheneylenediamine (1mmole, 0.108 gm) and p-amino benzaldehyde (1mmole, 0.121gm), was thoroughly ground with a pestle in a mortar at room temperature, then transferred to small conical, microwave power level (270 watt) for interval of time specified during 2-4min. after completion of the reaction, the reaction mixture was cooled to room temperature, washed with water and recrystallized from an ethanol solvent M.P. 288-290 ⁰C, yield 92%. CHN analysis that formula C₁₃H₁₁N₃ calculated C, 74.623 H, 5.306 N, 20.086; Found C, 76.592 H, 5.192 N, 19.887, Ultraviolet spectra λmax 212, 245 and 330 nm. FT-IR spectra νmax 3225, 3185, 3113, 2924, 1621, 1603, 1314, 1072 cm^{- 1}. ¹HNMR spectra δppm, (12.3, 1H), (7.25, 8H) and (6.5, 2H). ¹³CNMR spectra δppm, 120, 128, 121, 130, 133, 111, 170, 163, 113, and 163.

2- Synthesis of benzimidazole Schiff base.

Schiff base were synthesis by reaction amino phenyl benzimidazole (1mmole, 0.21gm) and terphthaldehyde (2mmole, 0.286gm) were mixed with each other dissolve in 20ml absolute ethanol was placed in small conical flask at room temperature, then glacial acetic acid 2-3 drop was added. The mixture was then exposed to microwave irradiation at 270Wpower for 3-5min. Complete of the reaction was tested by thin layer chromatography by using eluent (chloroform: methanol) ratio (3:7) respectively. The reaction mixture was then cold at room temperature. The yellow coloured Schiff base was obtained, which was recrystallized from ethanol and dried under pressure. The product was obtained in 89%, M.P. 278-280 ^oC. CHN analysis that formula C₃₄H₂₄N₆ calculated C, 79.053 H, 4.866 N, 16.276; Found C, 79.001 H, 4.777 N, 16.117, Ultraviolet spectra λmax 210, 245 and 330nm. FT-IR spectra νmax 3221, 3113, 2924, 1621, 1603, 1314, 1072 cm^{- 1}. ¹HNMR spectra δppm, (12.2, 2H) (8.3, 8H), (7.25, 8H) and (6.4, 6H). ¹³CNMR spectra δppm 120, 128, 121, 130, 133, 111, 170, 163, 117, 119, 113, 158, 163, and 155.

3-Synthesis Azetidin-2-one (β-Lactams)

i) - Preparation Chloro Acetyl Chloride:-

This reaction was carry out in the hood, chloro acetyl chloride was preparation from reaction chloro acetic acid (1mole, 0.94 gm) with phosphorous pentachloride (1mole, 0.21gm), the components of reaction were mixed warmly by glass rode until the solid component converted to liquid solution, the resulting liquid was purified by simple distillation in the boiling point 106⁰C (literature⁽³⁰⁾ 105 ⁰C).

ii) - Synthesis Azetidin-2-one

Azetidinone was synthesized by reaction of a mixture Schiff base (1mole, 0.517gm) in 20ml dioxane. Chloro acetyl chloride (1mole, 0.113gm) and triethylamine (2mole, 0.2gm) was placed in a small conical flask copped with funnel inside a microwave oven and irradiated at 270W power for 3-4min., after completion of the reaction (monitored by thin layer chromatography TLC by using eluent (hexane: ethyl acetate) ratio (3:7) respectively, it was then diluted with ice cold water. The solid product forms was washed in THF, filtered, dried and recrystallized from absolute ethanol, as a yellow solid, the product was obtained in 88%, M.P. 212-214^oC. CHN analysis that formula C₃₈H₂₆Cl₂N₆O₂ calculated C, 68.173 H, 3.913 N, 12.555;Found C, 68.008 H, 3.888 N, 12.42, Ultraviolet spectra λmax 215, 275 and 320 nm. FT-IR spectra νmax 3228, 3056, 1679, 1612, 1581, 1392, 1070 cm^-1. ¹HNMR spectra δppm, (7.00, 8H), (8.08, 1H), (7.35, 1H), (11.8, 2H). ¹³CNMR spectra δppm 135, 127, 110, 146, 156, 96, 156, 173, 57, 74, 116, 128, 106, 148 and 30.

4- Synthesis of Thaizolidinone

A mixture of (1mole, 0.517gm) Schiff base and mercaptoacetic acid (1mole, 0.1gm) in 20ml dry benzene, 0.2g of zinc chloride was added and placed in small conical flask at room temperature then the mixture exposed to microwave irradiation at 180W for 3min, This reaction was monitored by TLC. The resultant solution was cooled and poured in cold water. The separated solid was filtered, crystallized from ethanol to give crystalline yellow. yield 77%, Melting point 200-201^oC, CHN analysis that formula C₃₈H₂₈N₆O₂ calculated C, 68.652 H,5.553 N, 12.647; Found C, 68.265 H, 4.252 N, 12.454. Ultraviolet spectra λmax 222, 250, 295 and 328 nm. FT-IR spectra νmax 3224, 3113, 2988, 17350, 1620, 1533, 1150, 768 cm^-1. ¹HNMR spectra δppm (2.3, 4H), (6.8, 8H) , (7.3, 8H) ,(7.5, 4H) ,(8.4, 4H) and (12.4,1H).¹³CNMR spectra δppm, 170, 166,163, 158, 155, 153, 148, 144, 130, 128, 123, 120, 115, , 111, 105, 53.

RESULTS AND DISCUSSION:^(31-35)

Various benzimidazole derivatives were synthesized and confirmed by their elemental analysis, UV, IR, and NMR. CHN were situated within the range, which confirmed the validity of the suggested structure of the prepared compounds using reaction scheme 1:-

The purification benzimidazole compound was tested by thin layer chromatography (TLC) using different eluents. The best separation was obtained in mixture of (chloroform: methanol) (3:7) respectively as eluent. Then, the compounds were purified by using ethanol. The UV spectra of compound (A) was characterized by appearance of three bands in absolute ethanol, the first band appeared within the range (212-225) nm [ϵ= (580-2382) l. mole^-1. cm^-1] which was attributed to the (π-π*) for the aromatic system. The second band appeared in the range (245-250) nm [ϵ= (500-2485) l. mole^-1. cm^-1] which was attributed to the (π-π*) for the aromatic system. The third band appeared in the range (330-380) nm [ϵ= (305-2344) l. mole^-1. cm^-1] which was attributed to the (π-π*) transition of azomethane (C=N). The IR spectra of compound (A) was characterized by the appearance of the absorption band that was attributed to the (NH) stretching which appeared at (3224-3340) cm^-1 and (NH₂) stretching bands (3190-3340)cm^-1 which were present in spectrum of amino Benzimidazole, these fact confirmed the correct expected chemical structure of this compound. The ¹HNMR spectra of (A) compound showed multiplet signal within the region (6.5-7.25) ppm due to aromatic ring system. The other signal come back to the proton of imidazole ring in the region (12.3) ppm. ¹³CNMR spectra showed (10) peak; come ten carbon atoms, which exist in the structure.

The Benzimidazole Schiff base compound (B) was synthesized by the reaction of two mole of amino Benzimidazole group with terphthaldehyde in absolute ethanol. Glacial acetic acid was used as a catalyst for the protonation of carbonyl group in aldehyde compounds, using microwave irradiation in power 270W in different time; the reaction was monitored by TLC.

The purification Schiff base compound was tested by thin layer chromatography (TLC) using different eluents. The best separation was obtained in mixture of (chloroform: methanol) (3:7) respectively as eluent. Then, the compounds were purified by using ethanol and benzene. The mechanism of reaction can be explained in scheme 3, which showed the nucleophilic reaction attack amino Benzimidazole at the carbon atom of carbonyl group in the aldehyde with the elimination of water molecule at the end of reaction.

The UV spectra of all 2-azetidinone compounds were characterized by appearance of three bands in absolute ethanol, the first band appeared within the range (215-225) nm [ϵ= (600-1580) l.mole^-1. cm^-1] which was attributed to the (π-π*) for the aromatic system. The second band appeared within the range (275-280) nm [ϵ= (650-1814) l.mole^-1. cm^-1] which was attributed to the (π-π*) for the aromatic system. The third band appeared in the range (320-340) nm [ϵ= (292-1775) l.mole^-1. cm^-1] which was attributed to the (π-π*) transition of amide (N-C=O). The spectra of 2-azetidinone compound was characterized by the appearance of the absorption band that was attributed to the (C=O) stretching of amide which appeared at (1630-1690) cm^-1. The IR spectra of compound (C) showed a strong infrared absorption band in the region between (3224-3430) cm^-1 due to NH stretching. The ¹HNMR spectra of 2-azetidinone compound showed multiplet signal within the region (7-8) ppm due to aromatic ring system. While the proton of imidazole ring was showed signal in the region (11.8) ppm. The ¹HNMR spectrum appears two signals in the region (3.6-5.0) ppm which was due to aliphatic protons of azetidine ring, the first was due to proton that near nitrogen atom and the other from proton that near carbonyl group ¹³CNMR spectra showed (15) peak, come back to carbon of aromatic structure (twelve carbon) and three carbon of azetidine ring.

While the compound thaizolidinones (D) which showing four band at (222-295) nm were due to interferences transition (π-π*) aromatic heterocyclic ring with aromatic benzene ring addition to (n-π*) for carbonyl group come back to thaizolidinone compound (D).The structures of synthesized compounds were determined on the basis of their FTIR, Cyclisation with mercaptoacetic acid gave compound (D), this was characterized as the carbonyl group and C-S-C linkage vibrations, hence confirming the process of cyclisation. This compound showed the appearance of new vibration mode at (1720-1750) cm^-1, which was characterized as the peak for carbonyl group, and (1118-1190) cm^-1 for C-S. The formation of compound (D) was confirmed by appearance of new vibration modes at (1400-1440) cm^-1 and (1105-1150) cm^-1 which were characterized as the peaks for C=C and C-S. The IR spectra of compound (D) showed a strong infrared absorption band in the region between (3224-3430) cm^-1 due to NH stretching. ¹HNMR appears several signals for compound (D) showed at the region (6.8-8.4) ppm for the aromatic benzene rings. The CH₂ group of the thaizolidinone nucleus in (D) appears signal at δ (2.0-2.3) ppm. ¹³CNMR signals of thaizolidinone compounds were appears 16 line according to 16-carbon atom exist in the structure. Mechanism of the pericyclic reaction between an imine group and mercaptoacetic acid for preparing thaizolidinone ring systematically investigated. The breaking and formation of bonds occur simultaneously and thus the reaction proceeds via a single cyclic as show in scheme (2).

Biological Activities

The antibacterial ^{(39, 40)} activities of the series (A-D) have been carried out against some strain of bacteria. The result (Table 1) showed that prepared compounds are toxic against the bacteria. The Schiff base and azetidinone compounds were found more active against the above microbes. The comparison of the antibacterial activity of these compounds with Streptomycin shows that these compounds have almost similar activity.

The bacterial cultures for S. aureus, and E. coli were obtained from Department of biology University of Basrah. Iraq. The bacterial cultures were incubated at 30^oC for 24 hours by inoculation into nutrient agar. Schiff bases and azetidinone were stored dry at room temperature and dissolved 20mg/ml in dimethyl sulfoxide (DMSO). Antibacterial activities of each compound were evaluated by the agar disc-diffusion method. Mueller Hinton Agar Media (15 cm³) kept at 45^oC was poured in the petridishes and allowed to solidify. Poured Petri plates (9 cm) were incubated with 50μL of normal saline solution of above culture media (105-106 bacteria per ml). Discs injected with prepared Schiff base and azetidinone (50μL) were applied on the solid agar medium by pressing tightly. The Petri plates were placed at 37^oC for 24 hours. At the end of period, the inhibition zones formed on media were measured with a zone reader in millimeters.

Table 1:

Compound	*IZ Aureus* mm**	*IZ E. coli* mm**
A	5	8
B	4	7
C	8	9
D	6	6
Streptomycin	9	12

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