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Synthesis and fungitoxicity of aldimines and 4-thiazolidinones derived from 4-bromoaniline
Abstract
Condensation of 4-bromoaniline with benzaldehyde and substituted benzaldehydes (1-8) in equimolar ratio resulted in the formation of benzal-4-bromoaniline and its C-phenyl derivatives (1a-8a). Addition of thioglycolic acid to 1a-8a yielded the respective 4-thiazolidinone (1b-8b). The synthesized compounds were characterized on the basis of elemental analysis and spectral studies and were screened against five phytopathogenic fungi.
A simple and expedient multicomponent protocol was developed to synthesize 4-thiazolidinones by employing VOSO4 as a catalyst under ultrasonic irradiation. The significant features of this protocol includes shorter reaction time, high yields, low catalyst loading, and also the catalyst can be recovered and reused up to next four cycles without significant loss in catalytic activity. All the synthesized novel indazole compounds were evaluated for their antibacterial and anti-biofilm activities. Compounds 9n, 9o and 9q showed promising activity (MIC value of 3.9 μg/mL) against K. planticola (MTCC 530). They also exhibited significant bactericidal activity against K. planticola (MTCC 530) (MBC value of 15.6 μg/mL). Additionally, 9n, 9o and 9q inhibited biofilm formation (IC50 values ranging between 20.28-20.79 μg/mL) in this organism.
A series of N-benzylidenepyridin-2-amines (1a-j) were synthesized by heating 2-aminopyridine with different substituted aromatic aldehydes in the presence of toluene. The structures of the synthesized compounds were confirmed on the basis of IR, 1H NMR, 13C NMR and mass spectral data. The compounds 1a-j were screened for anthelmintic activity. Test results revealed that the compounds showed paralysis time of 0.27 to 1.52 min and death time of 0.42 to 4.42 min, whereas the standard drugs albendazole and piperazine citrate showed paralysis time of 0.54 and 0.58 min and death time of 2.16 and 2.47 min, respectively at the same concentration of 1% (m/V). Five compounds, N- (2-hydroxybenzylidene) pyridin-2-amine (1e), N- (4-bromobenzylidene) pyridin-2-amine (1g), N- (4-nitrobenzylidene) pyridin-2-amine (1h), N- (4-hydroxybenzylidene) pyridin-2-amine (1i) and N- (4-methoxybenzylidene) pyridin-2-amine (1j) showed the highest anthelmintic activity.
A series of N-benzylidenepyridin-4-amines (1a–1j) were synthesized by refluxing 4-aminopyridine with various substituted aromatic aldehydes in toluene. The structures of the synthesized compounds were confirmed on the basis of IR, 1H NMR, 13C NMR, and mass spectroscopy data. The synthesized compounds were screened for anthelmintic activity on earth worms. Tested compounds showed paralysis time from 0.44 to 2.46 min and death time from 1.03 to 3.50 min, whereas the standard drugs albendazole and piperazine citrate showed paralysis time of 0.54 and 0.58 min and death time of 2.16 and 2.47 min, respectively, at the same concentration of 1 % m/V. Three compounds, including N-(2-hydroxybenzylidene)pyridin-4-amine (1e), N-(4-nitrobenzylidene)pyridin-4-amine (1h), and N-(4-methoxybenzylidene)pyridin-4-amine (1j), showed significant anthelmintic activity compared to the standard drugs.
Condensation of malononitrile with 1-[4-(benzylideneamino)-phenyl]ethanones 1-10, the compounds containing both carbon-nitrogen and carbon-oxygen double bonds, in equimolar ratio results in the formation of solid products, identified as 2-benzylidenemalononitrile and its derivatives 1a-10a on the basis of elemental analysis and spectral studies. The reaction of 1-10 with two moles of malononitrile also yields the same products 1a-10a by a chemoselective attack of malononitrile on carbon-nitrogen double bond only rather than on both the reactive centres. The synthesized compounds 1a-10a have been evaluated for antifungal potential against Alternaria alternata, Colletotrichum capsici, Fusarium oxysporum, Myrothecium roridum and Ustilago tritici. Some of the compounds have been found to possess promising antifungal potential against the test fungi. Chemistry of multiple bonds has achieved a dramatic development in the past decades because these compounds have been used as substrates in the synthesis of industrial and biologically active compounds 1-3 . Moreover, the compounds containing carbon-nitrogen, carbon-oxygen and/or carbon-carbon double bond are known to possess biological activities 4 such as antimicrobial, antifungal, antitumor and nematicidal. Malononitrile reacts with carbonyl compounds to give condensation products 5 whereas such a reaction with imines have been reported to yield either addition-elimination products 6 or compounds containing heterocyclic rings 7 . The carbon-nitrogen double bond is intermediate in reactivity 8 between carbon-oxygen and carbon-carbon double bonds. In continuation of earlier work 9 on imine-ones, i.e. 1-(4-(benzylideneamino)phenyl)etha-none and its C-phenyl derivatives 10 , this communica-tion describes the chemoselective reaction of malononitrile with 1-(4-(benzylideneamino)phenyl)-ethanones and evaluation of products for antifungal activity.
Cyanoacetic acid reacted chemoselectively with carbon-nitrogen double bond of benzal-4-acetylaniliines, leaving the carbon-oxygen
double bond, considered to be more reactive, intact, leading to the formation of mono addition-elimination products rather
than bis attack at both the reactive centres, even when the reaction was carried out with two moles of cyanoacetic acid. The product
viz. benzalcyanoacetic acid and its derivatives were screened for their fungitoxicity against five pathogenic fungi.
Addition of thioglycollic acid to Schiffs bases of 3-chloroaniline (I-V) and 4-chloroaniline (VI-X) resulted in the formation of 4-thiazolidinones Ia-Va and VI-Xa respectively. The synthesized 4-thiazolidinones were characterized on the basis of elemental analysis and spectral studies and tested in vitro against Alternaria alternata, Fusarium oxysporum, Helminthosporium tetramera, Collectrichum capsici and Curvularia lunata by spore germination inhibition method. In general the 4-thiazolidinones (VIa-Xa) derived from Schiffs bases of 4-chloroaniline have been found to be more effective as compared to the 4-thiazolidinones (Ia-Va) derived from Schiffs bases of 3-chloroaniline.
A new methodology for the construction of 2-phenylimino-1,3-thiazolidin-4-one skeleton is described. Reaction of maleic anhydride (5a) or maleimides (5b, 5c) with thiourea (6) gave the corresponding 2-imino-1,3-thiazolidin-4-ones (7) and (9) respectively. The reaction proceeded with high yield in polar solvents. In non-polar solvents at high temperature, however, isothiocyanate (8) was formed as a by-product presumably by the pyrolysis of thiourea (6). The proposed mechanism of the reaction was discussed.