Studies of 5-aryl-4-(1H-benzo[d]imidazol-2-yl)-1-(4-(naphthalen-2-yl)thiazol-2-yl)pyrrolidin-2-one Derivatives

Novel series of heterocyclic compounds 2-aryl-1-(4-(naphthalen-2-yl)thiazol-2-yl)-5oxopyrrolidine-3-carboxylic acid derivatives (4a–h) and 5-aryl-4-(1H-benzo[d]imidazol-2-yl)-1-(4(naphthalen-2-yl)thiazol-2-yl) pyrrolidin-2-one derivatives (5a–h) have been synthesized by condensation of Schiff bases arylidine-[4-(2-naphthalenyl)thiazolyl]-2-amines (3a–h) with succinic anhydride. Synthesized heterocyclic compounds were duly characterized by physico chemical parameters, H-NMR, C-NMR and FT–IR spectral features. Schiff bases 3a–h have been synthesized from 4-(naphthalen-2-yl)thiazol-2-amine 1 and various aromatic aldehydes 2a–h. All novel synthesized compounds 4a–h and 5a–h were evaluated for their antibacterial activity against various Gram positive bacterial strains e.g. Bacillus subtilis [BS] and Staphylococcus aureus [SA] and Gram negative bacterial strains e.g. Salmonella typhimurium [ST] and Escherichia coli [EC]. Growth inhibition was compared with the standard drug ciprofloxacin. Antifungal activity was also carried out against different fungal strains e.g. Penicillium expansum [PE], Botryodiplodia theobromae [BT], Nigrospora sp. [NS], Trichothesium sp. [TS]. The antifungal drug, Ketoconazole was used as a positive control. Compounds 4a–h found less active as compare to compound 5a–h.


INTRODUCTION
Tremendous work has been carried out in the synthesis and development of heterocyclic compounds due to their important biological properties.2-Aminothiazoles and their derivatives have been used as pioneers for the synthesis of biologically active molecules [1][2][3][4].Some of these compounds possess anthelmintic activity, such as thiabedazole.Sulphathiazole possesses antibiotic activity.Nizatidine [5] compound possesses the thiazole moiety, which has clinical uses as an antiulcer drug.Farnetiaole has significant immunosuppressant activity, while fentiasac has clinical use as an anti-inflammatory agent [5].Recent research indicates that some of 2-aminothiazoline derivatives are inhibitors of enzymes such as kinurenine-3-hydroxylase [6] or possess inhibitory activity against the enzyme cyclin-dependent kinase [7].On the other hand, benzimidazole consists of benzene and imidazole and its derivatives have wide variety of biological activities, in addition to that the benzimidazole have played a very important role in the development of theory in heterocyclic chemistry and also extensively in organic synthesis [8].2substituted benzimidazole derivatives are found to be pharmacologically more potent and hence the design and synthesis of 2-substituted benzimidazoles are the potential area of research [9].Benzimidazole derivatives have played an important role in medicinal chemistry.In addition, they have been studied broadly [10][11][12][13][14][15] because of their ready accessibility and broad spectrum of biological activities.One of the authors had already synthesized the Schiff bases 3a-h [16].
When Schiff bases 3a-h was reacted with succinic anhydride, it undergoes a cycloaddition reaction.The formal cycloaddition process of imines and succinic anhydrides was first demonstrated by Castagnoli [17].Favorable substrates for this reaction have substituent, such as an aromatic ring, capable of stabilizing an enolate intermediate formed from iminolysis of the anhydride [18][19][20].The reaction of anhydride with dienophiles can be accelerated by deprotonation of the anhydride to form a dienolate anion [21] and finally converted to γ-lactams.Furthermore one-step synthesis of complex nitrogen heterocycles from imines with maleic anhydrides [22] and imines with succinic anhydrides [23] were carried out by Shaw and his research group.This prompted us to carry out our study by introducing thiazole and benzimidazole segments together.Herein we report the reaction of Schiff bases 3a-h with succinic anhydride to produce compound 4a-h and subsequently benzo[d]imidazol derivatives 5a-h with benzene-1,2-diamine.This work has not attracted any attention.Figure 1

MATERIAL AND METHODS
All common reagents and solvents were used of analytical grade and were used without further purification.Alumina-supported pre-coated silica gel 60 F254 thin layer chromatography (TLC) plates were purchased from the E. Merck (India) Limited, Mumbai and were used to check purity of compounds and, to study the progress of the reaction whereby TLC plates were illuminated under Ultraviolet light (254 nm), evaluated in I2 vapors and visualized by spraying with Draggendorff's reagent.Infrared spectra (FT-IR) were obtained from KBr pellets in the range of 4000-400 cm -1 with a Perkin Elmer spectrum GX spectrophotometer (FT-IR) instrument.

Antibacterial activity (in vitro)
Compounds 4a-h and 5a-h were screened for in vitro antibacterial activity against Gram-positive bacterial strains (Bacillus subtilis [BS] and Staphylococcus aureus [SA]) and Gram-negative bacterial strains (Salmonella typhimurium [ST] and Escherichia coli [EC] ) utilizing the agar diffusion assay [24][25].The wells were dug in the media with the help of a sterile metallic borer.A recommended concentration (100 μL) of the test sample (1 mg/mL in DMSO) was introduced in the respective wells.Other wells were supplemented with DMSO and reference antibacterial drug, ciprofloxacin, was served as negative and positive controls, respectively.The plates were incubated immediately at 37˚C for 24 hours.The activity was determined by measuring the diameter of zones showing complete inhibition (mm).Growth inhibition was compared with the standard drug.In order to clarify any participating role of DMSO in the biological screening, separate studies were carried out with the solutions alone of DMSO and they showed no activity against any bacterial strains.
[NS], Trichothesium sp.[TS].The antifungal drug, ketoconazole was used as a positive control.Antifungal screening for compounds 4a-h and 5a-h and positive control was performed at a recommended concentration.The fungal strains were grown and maintained on potato dextrose agar plates.The cultures of the fungi were purified by single spore isolation technique.Each compound 4a-h and 5a-h in DMSO solution was prepared for testing against spore germination of each fungus.The fungal culture plates were inoculated and incubated at 25± 2˚C for 48 h.The plates were then observed and the diameters of the zone of inhibition (in mm) were measured.The percentage inhibition for fungi was calculated after five days using the formula given below: Percentage of inhibition = 100(X-Y) / X Where, X = Area of colony in control plate and Y = Area of colony in test plate.

Synthesis of compounds 4a-h and 5a-h
To the best of our knowledge, compounds 4ah and 5a-h have not been reported previously.The characterization of the reaction product provided the first unambiguous proof of the successful synthesis of 2-aryl-1-(4-(naphthalen-2-yl) thiazol-2-yl)-5oxopyrrolidine-3-carboxylic acid derivatives.Elemental analyses of all compounds were in good agreement with proposed structures.The structures of all compounds were consistent with the FT-IR, 1 H NMR and 13 C NMR.The FT-IR spectrum of 4a-h showed the most relevant peaks of naphthalene ring, thiazole ring, other than typical absorptions arising from the band at 3490 cm -1 and 1709 cm -1 for carboxylic acid and 1720 cm -1 for C=O pyrrole-2-one [26].In the 1 H NMR spectroscopy, the signals in the range of 6.4-8.2 ppm were ascribed to the protons of the aromatic naphthalene, thiazole & benzene rings.The singlet at 11.8-11.9ppm was ascribed to the protons of carboxylic -OH group, which was further confirmed by 13 C NMR value i.e. 169 attributed to carboxylic carbon.The expected structure was thus clearly verified by the spectroscopic analysis which indicated moreover the absence of any detectable impurity, particularly of the two reagents used to prepare 4a-h.
Structures of the analogs 5a-h were consistent with the elemental analyses, FT-IR, 1 H NMR and 13 C NMR. FT-IR Spectral features provide valuable information.The FT-IR spectra of compounds 5a-h showed important changes with respect to those of the compounds 4a-h, which clearly confirmed that the reaction had taken place with good yields.Considerable differences to be expected were observed.The band at about 3510 cm -1 and 1710 cm -1 corresponding to -OH and C=O groups of carboxylic acid respectively in 4a-h were virtually disappeared from the spectra of 5a-h.Compounds 5a-h exhibit bands near 3670 cm -1 , 1680 cm -1 and 1290 cm -1 indicating the formation of benzimidazole derivatives.The singlet at about 10.8 ppm was ascribed to the protons of benzimidazole.Furthermore, the 13

Antibacterial activity
Based on the data from the antibacterial studies against both Gram-positive and Gram-negative bacterial strains (Figure 2), the following observations can be made.All compounds 4a-h and 5a-h exhibited antibacterial activity against both Grampositive and Gram-negative bacterial strains with zones of inhibition (ZOI) ranging from 20 mm to 41 mm (Figure 2).Among the analogs 5a-h, compound

Antifungal activity
Based on the screening data from the antifungal studies (Figure 4), the following observations can be made.All compounds 4a-h and 5a-h exhibited antifungal activity against different fungal strains (Figure 5).

1 H-
NMR and13 C-NMR spectra were acquired at 400 MHz on a Bruker NMR spectrometer using DMSO-d6 (residual peak at δ ~2.5 or ~ 39.5 ppm, 300 • K) as a solvent as well as TMS an internal reference standard.Micro analytical (C, N, H) data was obtained by using a Perkin-Elmer 2400 CHN elemental analyzer.The melting point was checked by the standard open capillary method.