Syntheses of 2-(6’-Fluorobenzothiazol-2’-ylamino) -4, 6-(disubstituted thiouriedo)-1,3-pyrimidine Derivatives as Antimicrobial Agents

A new series of 1,3-pyrimidine derivatives (3a-f) have been synthesized by reacting 2,4,6-Trichloropyrimidine with nucleophilic reagents 2amino-6-fluorobenzothiazole (1) in the presence of acetone. The (4,6dichloropyrimidin-2-yl)-amine (2) so produced was then reacted to two moles of phenylthiourea derivatives to yield title compounds (3a-f). The structural assessment of the compounds (3a-f) was made on the basis of spectral data. The synthesized compounds were screened for their in vitro growth inhibiting activity against different strains of bacteria viz., B. subtilis, E. coli, P. aeruginosa and S. aureus using agar diffusion technique. Compounds 3c and 3f exhibited highest antibacterial activity.


Introduction
Pyrimidine is the most important member of all the diazines as this ring system occurs widely in living organisms.Purines, uric acid, alloxan, barbituric acid and a number of antimalarial and antibacterial drugs also contain the pyrimidine ring 1,2 .Thiazole ring system is quite common in natural products, since it can be produced by cyclization of cysteine residues in peptides 3,4 .The most important of these is Vitamin B 1 (thiamine), which contains both a pyrimidine and a thiazole ring system.The bleomycin antibiotics, which have antitumour properties, are complex aminoglycosidic structures containing thiazole units.Several semi-synthetic beta lactams contain 2-aminothiazole units in the side chain 5,6 .
Since benzothiazoles, pyrimidines and thioureas all possess diverse biological activities [7][8][9][10][11] ; the aim of this study was to synthesize some new derivatives incorporating these nuclei and evaluate the prepared compounds for antibacterial activity.

Spectral data of compound 3a
IR: (KBr cm -1 ): 3230 (secondary amine N-H str), 1569 (secondary amine N-H ben), 3085 (Aromatic C-H str), 1622 (Aromatic C=C str) 1282 (Aromatic amine C-N str), 1120 (Aromatic C-F str); MS (FAB) m/z: 391(M-3).Yield 73.63%, Melting range: 265-270 °C.Compounds 3b-f were prepared by the aforesaid procedure 12 .The quantity of phenylthiourea derivatives was changed as per Table 1.Purity of all the compounds was checked on silica gel G plates using iodine vapour and UV lamp (at short and long wavelength) as the detecting agent.Thin layer chromatography was used for monitoring the progress of reaction and product formation.Melting points of the synthesized compounds were taken by open capillary method and are uncorrected.The infra-red spectra of the synthesized compounds were recorded on a SHIMADZU FTIR 8400 spectrophotometer using potassium bromide pellets.The FAB mass spectra were recorded on a JEOL SX 102/DA-6000 mass spectrometer/ data system using Argon/Xenon (6 kV, 10 m A) as the FAB gas.The accelerating voltage was 10 kV and the spectra were recorded at room temperature.The physical and analytical data of synthesized compounds is summarized in Table 2.

Antibacterial activity
Compounds 3a-f were screened for antibacterial activity against strains of Bacillus subtilis (MTCC 441), Pseudomonas aeruginosa (MTCC 424), Escherichia coli (MTCC 1573) and Staphylococcus aureus (MTCC 1430) using cylinder-plate method 13 .Culture media were prepared using aseptic and sterilization techniques 14 .Incubation period was 24 h at 37 °C in order to activate the bacterial strain.All the solutions of test compounds were prepared by dissolving 1 mg of testing sample in 1 mL of DMF (N, N-Dimethylformamide).This gives the conc. of sample 1000 µg/mL or 1000 ppm.Different dilutions such as 200 µg/mL and 100 µg/mL were prepared from the sample solution.A solution of DMF (10%) was used as control.Pure cultures of Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus were procured from Institute of Microbial Technology (IMTECH), Chandigarh, India and raised in conical flask (100 mL) containing potato dextrose agar (PDA).The evaluation of the antibacterial activity was done by measuring the zone of inhibition in different petri plates and taking average for each strain.
The yields of compounds fall in the range of 16% to 74%.The spectral data (IR and MS) are in good agreement with their structures.Scanning results of antimicrobial activity (Table 3) reveal that the known standard antibiotic produced a zone of inhibition of the order of 20-23 mm.Compounds 3c and 3f displayed good activity against E. coli, P. aeruginosa, B. subtilis and S. aureus.This could be due to the presence of fluoro and nitro groups.Other compounds (3a, 3b, 3d and 3f) exhibited less pronounced activity against the tested strains.

Conclusion
A series of 1,3 pyrimidine derivatives have been synthesized and characterized on the basis of IR and MS spectral data.The compounds exhibited antibacterial activity with two compounds showing good activity against selected strains.

Table 2 .
Physical and analytical data of the synthesized compounds (3a -f)

Table 3 .
Antibacterial screening data of compounds 3a-f