Synthesis and Bio-Evaluation of Novel N-(4-(8-Methoxy-2-Oxo-2 H - Chromen-3-Yl) Thiazol-2-Yl) Amide Derivatives

. In present work novel derivatives of substituted N-(4-(8-methoxy-2-oxo-2H-chromen-3-yl) thiazol-2-yl) amide have been synthesized. The solvent free reaction of 2-Hydroxy-3-methoxybenzaldehyde with Ethyl acetoacetate in presence of Piperidine catalyst produces 3-acetyl-8-methoxy-2H-chromen-2-one (C). Compound C was α- brominated using CuBr 2 and subsequently cyclized using Thiourea to produce 3-(2-aminothiazol-4-yl)-8-methoxy-2H-chromen-2-one as main scaffold ( E). This scaffold E was finally reacted with different Acid chloride to isolate title compound derivatives. The chemical structures of synthesized compounds were confirmed by 1 H-NMR, FT-IR and Mass spectral/LCMS analysis. The synthesized compounds were screened for potential Antimicrobial, Antifungal and Antimalerial activity.


Introduction
Thiazoles are one of the important of Heterocyclic compounds. They are present in some of the natural resources and found to possess moderate to good pharmacological value [1]. Many researchers have made considerable progress on the synthesis of novel Thiazole derivatives and reported their important medicinal properties. Thiazole derivatives are known to exhibit a wide spectrum of biological activities including anesthetic [2], inhibitory activity on apoptosis [3], antibacterial [4,5], anti inflammatory [6], anti tubercular [7], hypolipidemic and hypoglycemic [8], anti cancer [9] and many other important medicinal activity. The widespread use of Thaizole compounds is also confirmed by their use in the medicinal sector, some of the 2-amino thaizole derivatives are well established drugs and widely prescribed by the medicinal practitioners. For example Talipexol and Pramipexole having 2-aminothiazole moiety are used as antiparkinsonian drugs and dopamine agonists.
Coumarin and its derivatives are also represent one of the most biologically active classes of medicinal compounds. Coumarin derivatives are well known to possess wide spectrum of biological activity [10,11]. Many of such compounds have been proved to be active antibacterial [12] antifungal [13] agents. Coumarin is a flavonoids class compound and widely distributed in nature also. The synthetic and natural Coumarin is known to possess anti diabetic activity [14], anabolic and antioxidant properties [15], anti-Cancer [16], lipid lowering property [17], anti-coagulants [18] and anti-oxidant property [19].
Looking to the importance of both the nucleus we have incorporated both of them in a single moity to enhance the activity. In this article we have reported 20 new synthetic molecules, which are well characterized to prove the structures. Also, we have shown the biological screening of the synthesized molecules against gram +ve and gram -ve bacteria. Some synthesized compounds have shown good biological activity.

Material
All key raw materials, reagents and solvents were of commercial grade and used after further purification. All melting points were measured using open capillaries in a liquid paraffin bath and were uncorrected. The completion of reaction was monitored by thin layer chromatography using silica gel-G as absorbent and Methylene dichloride: Methanol was employed as mobile phase. The visualization of TLC was accomplished by UV light and Iodine. IR spectra (KBr pallet) were recorded on FT-IR, Perkin Elmer RX1 spectrophotometer and 1 H-NMR was determined in CDCl 3 /DMSO-d 6 solution on a Bruker Ac 400 MHz spectrometer data using TMS as internal standard (chemical shifts in δ ppm). Mass spectra were recorded on Shimadzu GCMS-QP-2010 model using Direct Injection Probe technique.

Methods
In the present work, novel caumarine derivatives were prepared by following general reaction scheme as shown in Scheme 1. The physical constants of synthesized compounds are mentioned in Table 1. Synthesized compounds were screened for antibacterial, antifungal and Antimalerial activity. The results of antibacterial, antifungal and Antimalerial activity are depicted in Table 2, Table 3 and Table 4 respectively.

Biological evaluation Antimicrobial Activity
All the synthesized compounds NS1-20 were evaluated in-vitro for antibacterial activity against gram positive Bacillus subtilis (MCMB-310) and gram negative Escherichia coli (MCMB-301) bacterial strains at the concentrations of 100µg/ml by bore plate method using DMF solvent and nutrient agar was employed as culture media. After 48 hrs of incubation at 37 ºC, the results were obtained in the form of cleared zone and were noted after the period of incubation was over. Correspondingly these compounds were evaluated for antifungal potencies against fungal strains Candida albicans (NCIM-3471) and Aspergillus niger (NCIM-545) at the concentration 100µg/ml per disc by paper disc diffusion method using DMSO solvent. The yeast Candida albicans cultured using a malt extract, glucose yeast extract peptone agar medium (MGYP medium) and for fungi Aspergillus niger potato dextrose agar medium was used. After 3-7 days of incubation at 30ºC,

Antifungal Activity
All the synthesized compounds NS1-20 were evaluated making it difficult to extract a clear structure-activity relationship analysis, some broad conclusions can still be drawn. These compounds were noticeably more active against Botrytis cinerea and Colletotrichum capsici, but lacked potency against Alternaria solani, Alternaria mali and Rhizoctonia solani, as illustrated by the absence of activity against these three kinds of fungi. Compounds NS-3, NS-4, NS-6 and NS-11 showed equivalent activity with the positive control Azoxystrobin against Alternaria mali. Secondly, the spectrum of antifungal activity is generally improved.

Anti malarial Activity
In this research work, firstly, all the derivatives were subjected to the susceptibility assay for Plasmodium falciparum to find out whether the synthesized derivatives possess anti-malarial activity. In this point of view, schizonticidal testing method was selected based on the ease of the test, less time consumption, robust, and economical. Compound NS-2, NS-6, NS-11 and NS-12 found good activity. Further to support the selection of schizonticidal as the test assay for the synthesized derivatives, schizonticidal possess the anti-malarial susceptibility of the derivatives. NS-10, 15 and 16 were found to be more efficient than Ampicillin (MIC=250 μg/mL) against gram +ve bacteria. All the newly synthesized compounds are not showed good antibacterial activity against S.Pyogenus (gram +ve). Overall, compound NS-13 possessed moderate to good antibacterial activity against gram negative bacterial strain. On the antifungal activity side, compound NS-1, 2, 9, 10, 16 are found equipotent to Greseofulvin (MIC=500 μg/mL) and compound NS 7, 13, 17, 18 and 19 are found to be more potent against C.Albicans; rest other synthesized compounds are not showed good antifungal activity and less potent than standard drugs. It was also found that all synthesized compounds possessed less antimalerial activity potential than standard drugs available in the market.

Conclusions
The novel series of amide derivatives of N-(4-(8-methoxy-2-oxo-2H-chromen-3-yl) thiazol-2-yl) have been synthesized in reasonably good yield by following simpler synthesis route using commercially available raw materials. The structure of all synthesized compounds are confirmed by FT-IR, Mass/LCMS and 1 H-NMR spectral study. The synthesized compounds were evaluated for potential biological property. Among all synthesized compounds, some of the compounds are found to possess reasonably good antimicrobial activity.