Synthesis and Studies of Novel Optically Active Schiff ’ s Base Derivatives and their Antimicrobial Activities

Several new Schiff’s base derivatives were prepared by condensing various substituted benzaldehyde with 1-(4-aminophenyl)-2-{4-[(S)-(4chlorophenyl)(phenyl) methyl]-1-piperazinyl}ethanone in presence of acid catalyst under reflux condition. All the compounds were characterized by elemental analysis and spectral studies. The newly synthesized compounds were evaluated for their antibacterial and antifungal activity.


Introduction
Schiff's base is a functional group or type of chemical compound containing a carbonnitrogen double bond with the nitrogen atom connected to an aryl group or an alkyl group but not hydrogen 1 .A Schiff's base (or azomethine) names after Hugo Schiff 2 .Schiff's bases can be synthesized from an aromatic amine and a carbonyl compound in a nucleophilic addition to a hemiaminal followed elimination of water to the imine 3 .Schiff's base ligands derived from salicylaldehyde and chiral amines have been widely applied in enantioselective cyclopropanation of styrenes 4 , asymmetric aziridination of olefins 5 , enantioselective epoxidation 6 , enantioselective ring opening of epoxides 7 , asymmetric oxidation of methyl phenyl sulfide 8 , enantioselective oxidation of silyl enol 9 and trimethylsilylcyanation of benzaldehydes 10 .Schiff's base containing heterocycles have attracted much attention due to their diverse biological activity such as anticancer 11 , antiviral [12][13] , fungicidal 14 , bactericidal 15 and anti-HIV 16 .

Experimental
All melting points were taken in open capillary tubes and are uncorrected.Specific optical rotations (SOR) were taken in Jasco digital polarimeter.Thin layer chromatography was performed on precoated TLC plates with silica gel (Merck 60 F 254 ) and detection was done by UV lamp (254 nm).The IR spectra were obtained on a Simadzu FTIR-8400S spectrophotometer using KBr pellets.The 1 H NMR spectra in DMSO-d 6 or CDCl 3 were recorded on Bruker WM 400FT MHz spectrometer and chemical shift were reported as parts per million (δ ppm) down field using TMS as internal standard.

Results and Discussion
The structures of substituted Schiff's base 3a-j were confirmed by elemental analysis, IR and 1 H NMR spectra.IR spectra showed absorption band at 1596 cm -1 indicated the stretching vibration of -CH=N (Schiff's base) which confirming the condensation of reactants.C-H stretching vibration of -CH 2 appeared at 2956 cm -1 and -C=O stretching appeared at 1666 cm -1 indicated which confirming the condensation of reactants.The other peaks of IR spectra prove the structure of Schiff's base derivatives. 1H NMR spectrum displayed signals for the presence of one imine proton (-CH=N) at 8.70 ppm (1H, s), one ketone group (-CO-CH 2 ) at 3.39 ppm (2H, s), which also confirms the condensation of reactants.

Biological screening Antibacterial activities
Antibacterial activities of all the compounds were studied against gram-positive bacteria [Staphylococcus aureus (MTCC96), Streptococcus pyogenes (MTCC442)] and gramnegative bacteria [Escherichia coli (MTCC443), Pseudomonas aeruginosa (MTCC424)] by the broth dilution method.Stock solutions of the series of compounds were prepared in DMSO.Each synthesized drug was diluted obtaining 2000 microgram/mL concentration, as a stock solution.Serial dilutions were prepared in primary and secondary screening.In primary screening 500 µg/mL, 250 µg/mL and 125 µg/mL concentrations of the synthesized drugs were taken.The active synthesized drugs found in this primary screening were further tested in a second set of dilution against all microorganisms.The drugs found active in primary screening were similarly diluted to obtain 100 µg/mL, 50 µg/mL, 25 µg/mL, 12.5 µg/mL, 6.250 µg/mL, 3.125 µg/mL and 1.5625 µg/mL concentrations.Under similar condition using Gentamycin, Ampicillin, Chloramphenicol, Ciprofloxacin, and Norfloxacin as a standard for comparison control experiment was carried out.An examination of the data reveals that all compounds showed antibacterial activity.The compounds 3e, 3j, were highly active against all four organisms employed.The compounds 3a, 3c, 3d, 3e, 3f, 3g and 3i were highly active against Escherichia coli (MTCC443) and Staphylococcus aureus (MTCC96).Results were presented in Table 2.

Antifungal activities
The compounds 3a-j were also screened for their antifungal activity against Candida albicans (MTCC227), Aspergillus niger (MTCC282) and Aspergillus clavatus (MTCC1323) at 2000 µg/mL concentration using broth dilution method.As shown in Table 2, the antifungal activity data clearly showed that the compound 3a-j having a good activity against Candida albicans but less active against Aspergillus niger and Aspergillus clavatus.The antifungal activity was compared with the known standard drugs greseofulvin, nystatin and the results were presented in Table 2.

Conclusion
The antimicrobial activity of 3a-j carried out against some strain bacteria.The results show that the prepared compounds were toxic against the bacteria.The comparison of the antibacterial and antifungal activity of these compounds with standard drugs show that the presence of nitro, methoxy and halogen (-Cl) group in the phenyl ring increases the activity.