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We have described the conventional and microwave method for the synthesis of N-(4-((2-chloroquinolin-3-yl)methylene)-5-oxo-2-phenyl-4,5-dihydro-1H-imidazol-1-yl)(aryl)amides 3a–l. It is observed that the solvent-free microwave thermolysis is a convenient, rapid, high-yielding, and environmental friendly protocol for the synthesis of quinoline based imidazole derivatives when compared with conventional reaction in a solution phase. Antimicrobial activity of the newly synthesized compounds is screened in vitro on the following microbial cultures: Escherichia coli (MTCC 443), Pseudomonas aeruginosa (MTCC 1688), Staphylococcus aureus (MTCC 96), Streptococcus pyogenes (MTCC 442), Candida albicans (MTCC 227), Aspergillus niger (MTCC 282), Aspergillus clavatus (MTCC 1323). All the synthesized bio-active molecules are tested for their in vitro antimicrobial activity by bioassay namely serial broth dilution. Among these compounds 3c, 3d, 3f, 3h and 3j show significant potency against different microbial strains. All the compounds have been characterized by IR, 1H NMR, 13C NMR and mass spectral data. On the basis of statistical analysis, it is observed that these compounds give significant co-relation.

This report describes the novel approach for the synthesis and exploration of hybrid molecules containing pyrimidine-based imidazole scaffolds as potent antimicrobial agents. The targeted compounds N-(4-arylidene-2-mercapto-5-oxo-4,5-dihydro-1H-imidazol-1-yl)-6-methyl-2-oxo-4-phenyl-1,2,3,4-tetrahydropyrimidine-5-carboxamides (5a–l) were achieved by the Knoevenagel condensation of a key precursor (4) with different aldehydes in good yields having moderate to excellent antimicrobial activity. The structural identification of final products was carried out by known classical spectral techniques like IR, 1H NMR, 13C NMR, and mass spectra. The obtained data indicated that the majority of the tested compounds exhibited good antibacterial activity over antifungal activity, particularly compounds 5j and 5b (having MIC values 12.5 μg/mL) showed a comparable effect to a standard antibacterial and antifungal agents.

In the present article, compounds 5-((substituted-2-chloroquinolin-3-yl)methylene)-2-(2-hydroxyphenylimino)thiazolidin-4-ones (3a–k), 1-(2-(2-(2-hydroxyphenylimino)-4-oxothiazolidin-3-yl)-2-oxoethyl)pyrimidine-2,4,6(1H,3H,5H)-trione (6) and 1-(2-(5-((substituted-2-chloroquinolin-3-yl)methylene)-2-(2-hydroxyphenylimino)-4-oxothiazolidin-3-yl)-2-oxoethyl)pyrimidine-2,4,6(1H,3H,5H)-triones (8a–k) have been synthesized by substituting C-5 and N-3 position of parent compound 2-(2-hydroxyphenylimino)thiazolidin-4-one (1). Structures of the newly synthesized compounds were assigned on the basis of elemental analyses, IR, 1H NMR, 13C NMR, and mass spectra. In vitro antimicrobial activity of target compounds (3a–k, 6 and 8a–k) was investigated against two Gram-positive, two Gram-negative bacteria and three fungal strains. Among the tested compounds (3e), (3f), and (3h) showed very good antifungal activity, while compound (6) showed very good antibacterial activity. Compounds (8e), (8f), and (8h) showed excellent antifungal and antibacterial activities.

New 5-arylidene derivatives, which bear a fluorine atom in the 4th position of the benzoyl group as starting compound, have been synthesized by the condensation of 4-fluoro-N-(4-methyl-5-(2-(4-oxo-3-phenylthiazolidin-2-ylidene)hydrazinecarbonyl)thiazol-2-yl)benzamide and Knoevenagel condensation with aromatic aldehydes to form N-(5-(2-(5-(arylidene)-4-oxo-3-phenylthiazolidin-2-ylidene)hydrazinecarbonyl)-4-methylthiazol-2-yl)-4-fluorobenzamides (6a–o) through conventional and microwave methods. The structures of synthesized compounds were established by spectroscopic as well as spectrometric techniques (IR, 1H NMR, 13C NMR, 19F NMR spectroscopy and mass spectrometry). Antimicrobial screening of 5-arylidene derivatives 6a–o was done against Gram-positive bacteria (Staphylococcus aureus and Streptococcus pyogenes), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and fungi (Candida albicans, Aspergillus niger, and Aspergillus clavatus) using serial broth dilution method. Compounds 6g and 6j were found to be most active at MIC 12.5 μg/mL against selected bacterial strains and compound 6e was found to be most active at MIC 25 μg/mL against selected fungal strains. It has been further observed that the presence of fluorine atom at the 4th position of the benzoyl group in the final compounds is essential for enhancing the antimicrobial activity.

A series of 2-(5-(2-chloro-6-methylquinolin-3-yl)-3-(aryl)-4,5-dihydro-1H-pyrazol-1-yl)thiazol-4(5H)ones (4a–l) were synthesized and characterized by IR, 1H NMR, 13C NMR, and mass spectra. All the synthesized compounds were tested for their in vitro antimicrobial activity against Escherichia coli (MTCC 443), Pseudomonas aeruginosa (MTCC 1688), Staphylococcus aureus (MTCC 96), Streptococcus pyogenes (MTCC 442), Candida albicans (MTCC 227), Aspergillus niger (MTCC 282), and Aspergillus clavatus (MTCC 1323) by serial broth dilution. Compounds 4e, 4f, 4g, 4i, 4j, and 4l were the most distinctive derivatives identified in present study because of their remarkable in vitro antimicrobial potency.

The synthesis of a novel series of 2-(5-(2-chloro-6-fluoroquinolin-3-yl)-3-(aryl)-4,5-dihydro-1 H -pyrazol-1-yl)thiazol-4(5 H )-ones ( 4a–l ) and N -(4-(2-chloro-6-fluoroquinolin-3-yl)-6-(aryl)pyrimidin-2-yl)-2-morpholinoacetamides ( 7a–l ) are described in the present paper. The chemical structures of compounds have been elucidated by IR, 1 H NMR, 13 C NMR and mass spectral data. Antimicrobial activity was measured against Escherichia coli (MTCC 443), Pseudomonas aeruginosa (MTCC 1688), Staphylococcus aureus (MTCC 96), Streptococcus pyogenes (MTCC 442), Candida albicans (MTCC 227), Aspergillus niger (MTCC 282) and Aspergillus clavatus (MTCC 1323) by serial broth dilution. Evaluation of antimicrobial activity showed that several compounds exhibited greater activity than reference drugs and thus could be promising new lead molecules.

A series of compounds 2-(5-(3-(4-fluorophenyl)-1-phenyl-1 H -pyrazol-4-yl)-3-(aryl)-4,5-dihydro-1 H -pyrazol-1-yl)thiazol-4(5 H )-ones ( 4a – q ) were synthesized and structures of these compounds were elucidated by spectral (IR, 1 H NMR, 13 C NMR, mass spectra) analysis. Synthesized compounds were screened for in vitro antibacterial activity against the representative panel of Gram-positive ( Staphylococcus aureus , Streptococcus pyogenes ) and Gram-negative ( Escherichia coli , Pseudomonas aeruginosa ) bacteria. These compounds were also tested for their inhibitory action against strains of fungi ( Candida albicans , Aspergillus niger , Aspergillus clavatus ). The synthesized compounds showed potent inhibitory action against the test organisms.

A new series of compounds 2-((1-(4-(4-arylidene-2-methyl-5-oxo-4,5-dihydro-1H-imidazol-1-yl)phenyl)ethylidene)hydrazono)thiazolidin-4-ones (4a–o) have been synthesized under conventional and microwave irradiation method. All compounds were characterized by IR, 1H NMR, 13C NMR and mass spectra. Newly synthesized compounds were screened for their antibacterial and antifungal activities on Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Staphylococcus pyogenes, Candida albicans, Aspergillus niger and Aspergillus clavatus by bioassays, namely serial broth dilution. The synthesized compounds showed potent antimicrobial activity against tested microorganisms. Compounds 4h, 4j, 4m and 4n were the most potent amongst tested compounds.

A series of novel compounds N-(4-(2,6-dichloroquinolin-3-yl)-6-(aryl)pyrimidin-2-yl)-2-morpholinoacetamides (5a–l) were synthesized by a series of multistep reactions. Newly synthesized compounds have been characterized by IR, 1H NMR, 13C NMR, and mass spectral data. Antimicrobial screening of title compounds 5a–l was examined against Gram-positive bacteria (Staphylococcus aureus and Streptococcus pyogenes), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and three fungi (Candida albicans, Aspergillus niger, and Aspergillus clavatus) by serial broth dilution method. Synthesized compounds showed potent inhibitory action against test organisms. Screened compounds 5e–g and 5i–l were associated with considerably higher antibacterial and antifungal activities than commercially used antibiotics.

The rising prevalence of multi-drug resistant Gram-positive, Gram-negative bacteria and fungi continues to provide momentum for search and development of novel active antimicrobial agents against these pathogens. In continuation to this, the present article deals with the synthesis and antimicrobial activity of a novel series of (3-(1H-benzo[d]imidazol-2-yl)-5-(aryl)-4,5-dihydro-1H-pyrazol-1-yl)(pyridin-4-yl)methanones 4a–n, synthesized by the reaction of benzimidazolyl chalcones with isoniazide 3. The structures of synthesized compounds were elucidated on the basis of IR, NMR, and mass spectra. The newly synthesized compounds 4a–n were screened for their antimicrobial activity against different strains of bacteria and fungi using serial broth dilution method. Compounds 4d, 4f, 4h, and 4g were found to be most active with MIC of 25 μg/mL against selected bacterial strains. Compounds 4c, 4g, and 4n were found to be most active with MIC of 100 μg/mL against selected fungal strains.

A series of compounds 4-(4-(4-aminophenyl)-6-(aryl)-1,6-dihydropyrimidin-2-ylthio)butanenitriles 5a–l were synthesised by the reaction of allyl cyanide 4 with 3a–l. Compounds 3a–l were prepared from reaction between various chalcones 1a–l and thiourea in presence of catalytic amount of potassium hydroxide. Compounds 3a–l, and 5a–l were prepared by classical as well as MWI methods. Structures of the compounds were characterized by IR, 1H NMR, 13C NMR and mass spectral data. The newly synthesized compounds 5a–l were screened for their antimicrobial activity against different strains of bacteria and fungi using serial broth dilution method. Compounds 5e, 5g and 5k were found to be most active with MIC of 25 μg/mL against selected bacterial strains, while compound 5d, 5f, 5j and 5k were found to be most active with MIC 50 μg/mL against selected fungal strains.

In order to search for new bioactive molecules with significant antimicrobial action, a series of 1,2,4-triazole and naphthalene analogs bearing structurally diverse substituents, N-(3-mercapto-5-(naphthalen-1-yl)-4H-1,2,4-triazol-4-yl)(aryl)amides 3a–l were synthesized in good yield by a multi-step synthetic procedure. Their antimicrobial activity was screened against various Gram-positive and Gram-negative bacteria and fungi. Compounds 3a, 3f, 3g, 3j, and 3k exerted strong inhibition of the investigated bacterial and fungal strains compared to control antibiotic ampicillin and antifungal griseofulvin. On the basis of statistical analysis, it is observed that the compounds give significant co-relation. All the synthesized compounds have been characterized by IR, 1H NMR, 13C NMR, and mass spectral data.

A new series of quinolinylpyrazolinylthiazole derivatives (V) (12 examples) is synthesized from chalcones (I).

A variety of new chromenylpyridinyl sulfonamides (VI) (13 examples) are synthesized and screened for their antibacterial and antifungal activities.

A variety of new fluorobenzamide derivatives (X) (15 examples) are synthesized using conventional or microwave chemistry and evaluated for their antimicrobial activities.

Two novel series of quinoline derivatives substituted with thiazolylpyrazole (V) or pyrimidine moieties (XI) are synthesized (yields not given) and screened for their antimicrobial activities.

The synthesized compounds (V) show potent inhibitory action against Gram-positive and Gram-negative bacteria and against different strains of fungi.

It is our ongoing effort to search new bio-active molecules and as a part of this, several chemical processes like condensation, cycloaddition were carried out to furnish 2-((1-(4-(4-(arylidene)-5-oxo-2-phenyl-4,5-dihydro-1 H -imidazol-1-yl)phenyl)ethylidene)hydrazono)thiazolidin-4-ones ( 4a – o ). All compounds were characterized by IR, 1 H NMR, 13 C NMR and mass spectra. Newly synthesized compounds were screened for their antibacterial and antifungal activities on Escherichia coli , Staphylococcus aureus , Pseudomonas aeruginosa , Staphylococcus pyogenes , Candida albicans , Aspergillus niger and Aspergillus clavatus by bioassay namely serial broth dilution. On the basis of statistical analysis, it was observed that these compounds showed significant co-relation. The synthesized compounds showed potent antimicrobial activity against test microorganisms.