Synthesis and antimicrobial activity of succinimido ( 2-aryl-4-oxo-3-{ [ ( quinolin-8-yloxy ) acetyl ] amino }-1 , 3-thiazolidin-5-yl ) acetates

8-Hydroxyquinoline 1 reacts with ethyl chloroacetate in the presence of anhydrous K2CO3 to produce ethyl (quinolin-8-yloxy)acetate 2. Treatment of 2 with hydrazine hydrate forms 2(quinolin-8-yloxy)acetohydrazide 3, which on condensation with various aldehydes 4a-e gives N'-{[(1Z)-arylmethylene]-2-(quinolin-8-yloxy)}acetohydrazides 5a-e. These, on cyclization with mercaptosuccinic acid, yield (2-aryl-4-oxo-3-{[(quinolin-8-yloxy)acetyl]amino}-1,3-thiazolidin5-yl) acetic acids 6a-e. Compounds 6a-e are further converted into acid chloride derivatives 7ae by reaction with thionyl chloride. Subsequent treatment of 7a-e with N-hydroxysuccinimide in the presence of TEA furnishes the title compounds 8a-e. Antibacterial and antifungal activities of the final compounds have been evaluated and all the compounds have shown significant inhibition of bacterial and fungal growth.


Introduction
The importance of the quinoline nucleus has been well demonstarted as illustrated by the large number of patents employing such species as chemotherapeutic agents.A number of biological activities have been associated with quinoline-containing compounds such as anti-inflammatory, antiallergic 1 , antimalarial 2 , antibacterial 3 , antiproliferative 4 , anticancer 5,6 and antiparasitic 6 activities.Similarly, various thiazolidinones [7][8][9] have attracted considerable attention as they are also endowed with a wide range of pharmaceutical activities including CNS-depressant 10 , anaesthetic 11 , anticonvulsant 12 , antibacterial 13,14 , antiviral 15 and antitumor 16 .Furthermore, drug research and development has led to the discovery of new pharmacologically active agents, including imidoxy 17,18 compounds such as phthalimidoxy 19 and succinimidoxy 20 .Succinimidoxy ARKAT derivatives were tested against different cancer cells 21 and also have been used in peptide synthesis 22 .They also possess a strong anti-convulsant activity 23 .In the present study, we have synthesized a new class of combinational molecules in which all of these moieties are present.The structures of the compounds synthesized were assigned on the basis of elemental analysis, IR, NMR and Mass spectral data.These compounds were evaluated for their antimicrobial screening.

Results and Discussion
Ethyl (quinolin-8-yloxy)acetate 2 has been synthesized by condensation of 8-hydroxyquinoline 1 with ethyl chloroacetate in dry acetone for 18 h.In the IR spectrum of compound 2, bands in the range of 1747 cm -1 were obtained due to C=O stretching, as expected for the formation of 2. In the 1 H NMR spectrum, signals were found at δ 4.97 (singlet), 3.22 (quartet) and 2.28 (triplet), which showed the presence of a OCH 2 COOC 2 H 5 group.Compound 2, on treatment with hydrazine hydrate, yielded 2-(quinolin-8-yloxy)acetohydrazide 3.In the IR spectrum of 3, N-H stretching was observed at 3336-3257 cm -1 , which was absent in precursor 2. In the 1 H NMR spectrum, the characteristic proton of the CONH group was observed at δ 8.09 as a singlet.Compound 3, on reaction with various aldehydes 4a-e, gave N'-{[(1Z)-arylmethylene]-2-(quinolin-8-yloxy)}acetohydrazides 5a-e, which in turn afforded (2-aryl-4-oxo-3-{[quinolin-8yloxy)acetyl]amino}1,3-thiazolidin-5-yl) acetic acids 6a-e on cyclization with mercaptosuccinic acid.The structures of the products were elucidated further on the basis of the C-S-C linkage in the five membered ring, which caused a weak but sharp absorption band at 760-710 cm -1 in all the compounds.A broad band in the range 3223-2891 cm -1 was obtained due to the OH stretching vibration and the C=O group was observed as a strong, sharp band at 1733-1674 cm -1 in all these compounds.The thiazolidinone CH was observed at δ 3.58-3.29ppm as a triplet and the CH 2 protons at δ 3.27-3.04ppm as a doublet, which indicated the formation of 6a-e.Compounds 6a-e were further converted into acid chloride derivatives 7a-e by reaction with SOCl 2 .Formation of the products was confirmed by disappearance of the IR band at 3223-2891 cm -1 due to the OH group and the appearance of a new band at 775-710 cm -1 due to the C-Cl bond.Subsequently, the chlorine atom in CH 2 CO-Cl was replaced by the succinimidoxy group to give the title compounds 8a-e.In the MS spectra of the latter, the molecular ion peak indicated the formation of compounds 8a-e.Attempts to use anhydrous K 2 CO 3 and Na 2 CO 3 in acetone to condense 7a-e with N-hydroxysuccinimide gave poor yields and the stronger base, NaH in THF, gave a sticky product that could not be crystallised.Better yields were obtained when TEA in DMF was used.

Scheme I Scheme 1
The synthesized compounds 8a-e were screened "in vitro" for antimicrobial activity.From the data presented in Table 1, it is clear that compound 8b is highly active against ARKAT Staphylococcus aureus, Staphylococcus albus, Streptococcus faecalis, Klebsiella pneumoniae and Pseudomonas aeuroginosa as compared to the standard (amicacin), but shows only moderate activity against Escherichia coli and Proteus mirabilis.Other compounds exhibit moderate to good antibacterial activity against all organisms.Similarly, 8b and 8e exhibit good antifungal activity against Candida albicans and Aspergillus fumigatus as compared to the standard drug used (fluconazole).The remaining compounds are moderately active against these two micro-organisms (C.albicans and A. fumigatus).It can be concluded that the antimicrobial activity of such compounds may change by introduction or elimination of a specific group.
* Activity index = Inhibition area of the sample/inhibition area of the standard.C 1 = Amicacin; C 2 = Fluconazole.Diameter of disc is 5 mm

Antimicrobial screening
The disc-diffusion method 24 was used for the screening of anti-microbial activity.The antibacterial activity of the synthesized compounds 8a-e was tested against gram-positive bacteria i.e.Staphylococcus aureus, Staphylococcus albus, Streptococcus faecalis and gramnegative bacteria i.e., Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeuroginosa, Proteus mirabilis, Salmonella typhi using a nutrient agar medium.The antifungal activity of the compounds was screened against Candia albicans and Aspergillus fumigatus using Sabouraded dextrose agar medium.The sterilized medium (autoclaved at 121°C for 15 min.)was innoculated with the suspension of the micro-organisms and poured into a Petri dish to give a depth of 3-4 mm.The paper impregnated with the synthesized compounds 8a-e (300 µg/ml in DMF) was placed on the solidified medium.The plates were pre-incubated for 1 h at room temperature and incubated at 37° for 24 h and 48 h for antibacterial and antifungal activity, respectively.Amicacin (300 µg/ml) was used in anti-bacterial activity studies, whereas fluconazole (300 µg/ml) was used in antifungal activity studies, as reference compounds.After incubation, the relative susceptibility of the micro-organisms to the potential antimicrobial agent is demonstrated by a clear zone of growth inhibition around the disc.The inhibition zone caused by the various compounds on the micro-organisms was measured and the activity rated on the basis of the size of the inhibition zone.The observed zone of inhibition is presented in Table 1.

Table 1 .
Antimicrobial activity of compounds 8a-e.Zone of inhibition (mm) (activity index)* All melting points were determined in open capillary tubes and are uncorrected.The IR spectra were recorded on a Perkin-Elmer 1800 spectrophotometer.The 1 H NMR spectra were scanned on a DRX-300 MHz.Spectrometer (300 MHz) in CDCl 3 /DMSO d 6 using TMS as the internal standard and chemical shifts are expressed in δ ppm.The mass spectra were recorded on a Jeol SX-102 (FAB).m-Nitrobenzyl alcohol (NBA) was used as matrix.