Synthesis and Screening of Biologically active Schiff bases of Benzothiazoles and its Zinc and Lanthanum metal complexes

The substituted 2-Aminobenzothiazole and ethyl 2-(4-formyl-3-hydroxyphenyl)-4methylthiazole-5-carboxylate in methanol mix together and heat the reaction mixture for overnight, It gives Schiff’s bases (derivatives of substituted aminobenzothiazole) 3.This compound 3 when treated with zinc chloride it gives zinc metal complex of Schiff’s bases 4 and if compound 3 was treated with Lanthanum chloride gives Lanthanum metal complex of Schiff’s bases 5, which shows marked biological activities.


INTRODUCTION
The benzothiazole derivatives show wide range of biological activities which include analgesic 1 , anti-inflammatory 2 , antiviral 3 , antibacterial 4 and anticancer activities.
Preparation and screening of 2-Aminobenzothiazole derivatives in vitro as potential antimicrobial activity, which shows remarkable antifungal activity 5 . Hugo Schiff reported the condensation of primary amines with carbonyl compounds known as Schiff's bases which reported in 1864 6 . Nowadays, Schiff base coordination chemistry has expanded enormously in the field of research. Advantages of Schiff base complexes for biological applications, bioinorganic chemistry, material science, supramolecular chemistry, catalysis and separation and summarize processes, and formation of compounds with unusual properties and structures has been well recognized and reviewed. 7 Schiff Bases are characterized by the Imine (-N=CH-) group which carries out the mechanism of transamination and racemization reaction in biological system 8,9 Several Schiff's bases are listed to get outstanding antibacterial, antifungal and anticancer activities 10,11,12,13 .
Lanthanide complexes showed importance in cancer diagnosis and therapy. Lanthanide-based tiny molecules as well as nonmaterial's have been scrutinize as cytotoxic agents and constraint, in photodynamic treatment, radiation therapy, drug delivery. 14 The Zn (II) complex has a very interesting and varied pharmacological activity. Zn (II) complex are effective against gastric mucosal injuries 15,16,17 shows a potent anti-ulcer activity and is also effective against Helicobacter pylori, a causative agent for stomach ulcers.

Present work Experimental Procedure for Schiff's bases
The equimolar solutions of 2-aminoben-zothiazole and ethyl 2-(4-formyl-3-hydroxyphenyl)-4-methylthiazole-5-carboxylate were stirred in 10 mL of methanol. The reaction mixture was then heated overnight for 12 to 14 hours. The completion of reaction was monitored by thin layer chromatography (TLC) using hexane: Ethyl Acetate (8:2). The reaction mixture was gradually cool at room temperature. The reaction mixture was then filtered and washed with 5 mL of methanol. The wet sample was dried at 50 0 C in oven for 5 hours. The product obtained was yellow dry solid with the yield of 95%.

EXPERIMENTAL
Infrared spectra were recorded in KBr disc on Shimadzu FTIR Spectrophotometer. 1 H NMR spectra were recorded on a Bruker Avance II 400 MHz spectrophotometer DMSO-d 6 as a solvent and TMS as an internal standard (chemical shift in δ values). Mass spectra were analyzed in Finnigan mass spectrometer. Purity of the compounds was checked by TLC on silica gel plates.

Experimental procedure for zinc metal complexes Synthesis of Bis[ethyl2-(4-hydroxy-3-{(E)-[(1,3benzothiazol-2-yl)inimo]methyl} phenyl)-4methyl-1,3-thiazole-5-carboxy-late]zinc(II)
The solution of ligand 3a-3e (2.36 mmol) was stirred in 30 mL methanol. Zinc chloride 18 solution (1.18 mmol in 10 mL methanol) was added dropwise in reaction mixture. The pH of 5.6 was adjusted by using sodium carbonate. The reaction mixture was then heated at 65-70 0 C for overnight. The reaction mixture was allowed to cool at room temperature. The volume of reaction was reduced to 10 mL under vacuum. Then 5 mL of water was added by using dropping funnel in reaction mixture. It was stirred for 30 min and then filtered under vacuum. The wet solid obtained was recrystallized in water and methanol (7:3) at 60-65 0 C. The orange crystalline product obtained (4a) was then dried at 75-80 0 C for 12 hours.

Experimental procedure for lanthanum metal complexes Synthesis of Bis[ethyl2-(4-hydroxy-3-{(E)-[(1,3benzothiazol-2-yl)inimo]methyl} phenyl)-4methyl-1,3-thiazole-5-carbo -xylate]lanthanum(II) chloride
The equimolar amount of ligand 3a to 3e & Lanthanum chloride (1.18mmol in 10 mL of methanol) were mixed in 30 ml methanol. It was added drop wise in reaction mixture and pH 5.6 was maintained by using sodium carbonate. Then heat mixture was to 65-70 0 C for overnight 10 to 12 hours. The reaction mixtures gradually cool to ambient temperature. The volume of reaction was reduced to 10 mL under vacuum. Then 5 mL water was added drop wise to the reaction mixture with stirring for 30 minute. The reaction mixture filtered under vacuum. The wet solid was recrystallized using water and Methanol (7:3) at 60-65 0 C and the orange crystalline product (5a) was dried for 12 hours.

Biological activity Antibacterial assay
Antimicrobial of ligands and its metal complexes screened against three gram positive Staphylococcus aureus 1, Staphylococcus aureus 2 and Bacillus subtilis. Two Gram-negative like Klebsiella pneumonia and Escherichia coli and fungi Candida albicans to asset their potency as antimicrobial agent by minimum inhibition concentration (MIC) using microbiological method 19 . The test inoculums Staphylococcus aureus 1 ATCC 6538, Staphylococcus aureus 2 ATCC 33591, Bacillus subtilis ATCC 6051, Klebsiella pneumonia ATCC 4352, E coli ATCC 8739 and Candida albicans ATCC 24433. All ligands and its metal complexes have to be done with brain heart infusion (BHI) for Minimum inhibition concentration (MIC). Ingredients in brain heart Infusion 500 g/Liter contain Calf brain infusion form 200 g, beef heart infusion form 200 g, protease peptone 10 g dextrose 2 g sodium chloride 5 g disodium phosphate 2.5 g. Fluconazole and ciprofloxacin are used as standard. Micro broth dilution method was used for standard drugs. For facultative anaerobes, tubes were incubated at 37 0 C for 48-72 h in carbon dioxide jar.

RESULTS AND DISCUSSION
Schiff bases are amorphous powder and metal complexes having crystalline powder. All the metal complexes are insoluble in water but soluble in DMSO. Metal complexes are stable at room temperature. On heating, they decompose at higher temperature. Analytical data of ligand and metal complexes are summarized below. Mass Spectroscopy Formation of Schiff bases is confirmed by presence of intense molecular ion peak.

CONCLUSION
A l l a r e n o ve l S c h i f f b a s e s h ave been synthesized and characterized by using different 2-amino benzothiazole derivatives and salicylic aldehyde derivative [Ethyl-2-(3formyl-4-hydroxyphenyl)-4-methyl-1, 3-thiazole-5-carboxylate]. Novel transition metal complexes have been synthesized and characterized by spectroscopic techniques from above novel Schiff bases and zinc and lanthanum metal.
The spectral data shows that the stoichiometric ratio of the metal and ligand is 1:2. In zinc metal complexes, the ligand is bidentate which is coordinates through azomethine nitrogen of Schiff base and oxygen from salicylic fragment to the zinc metal. Similarly in lanthanum complexes, the ligand is tridentate which is coordinates through azomethine nitrogen of Schiff base, oxygen from salicylic aldehyde fragment and nitrogen from benzothiazole ring.
In vitro data shows the all lanthanum complexes shows the therapeutic benefit, particularly treatment for antifungal agents C. albicans, E.coli, Klebsiella, Staph 1 staph 2.