Quinoline Hydrazide/Hydrazone Derivatives: Recent Insights on Antibacterial Activity and Mechanism of Action

Antibiotics are becoming gradually ineffective due to drug resistance, leading to greater difficulty in the treatment of infectious diseases. Therefore, the development of new chemical entities with different mechanisms of action is essential in the fight against resistant microorganisms. Various studies have shown that quinoline hydrazide/hydrazone derivatives possess several biological activities, such as antimalarial, antitubercular, anticancer, anti-inflammatory, and antimicrobial. Among these activities, the antibacterial activity of quinoline hydrazide/hydrazone derivatives is noteworthy. The synthetic flexibility of the quinoline ring has led to the development of a wide range of structurally diverse quinoline hydrazide/hydrazone derivatives, which can act at various bacterial targets such as DNA gyrase, glucosamine-6-phosphate synthase, enoyl ACP reductase, and 3-ketoacyl ACP reductase. This review emphasizes the antibacterial potential of various reported quinoline hydrazide/hydrazone derivatives based on substitution in the quinoline ring. The antibacterial activity of various metal-quinoline hydrazide/hydrazone complexes is also discussed. The aim of this review is to assemble and scrutinize the latest reports in this promising area of drug development.

A general strategy for the synthesis of α-trifluoromethyl- and α-perfluoroalkyl-β-lactams via palladium-catalyzed carbonylation

β-Lactam compounds play a key role in medicinal chemistry, specifically as the most important class of antibiotics. Here, we report a novel one-step approach for the synthesis of α-(trifluoromethyl)-β-lactams and related products from fluorinated olefins, anilines and CO. Utilization of an advanced palladium catalyst system with the Ruphos ligand allows for selective cycloaminocarbonylations to give diverse fluorinated β-lactams in high yields.

Crystal structures, Hirshfeld surface analysis and Pixel energy calculations of three trifluoromethylquinoline derivatives: further analyses of fluorine close contacts in trifluoromethylated derivatives

As many studies have revealed, the introduction of a CF3 group into an organic compound can result in significant enhancement of biological activity. Factors which lead to this enhancement are thus of great interest. To investigate further this area, we have looked at the ability of fluorine to form close contacts with various atoms in organic compounds, e.g. F⋯F, F⋯O/O⋯F, F⋯C/C⋯F, H⋯F/F⋯H, and F⋯N/N⋯F, as indicated from crystal structure determinations and Hirshfeld analysis studies on trifluoromethylated compounds. Herein we first report the crystal structures, Hirshfeld surface analyses (HSA), and Pixel energy calculations of three trifluoromethylated quinoline derivatives, namely 2-(trifluoromethyl)quinolin-4-ol, 1, 4-ethoxy-2-(trifluoromethyl)quinoline, 2, and N 1-(2,8-bis(trifluoromethyl)quinolin-4-yl)ethane-1,2-diamine, 3. Of particular interest is the determination of the various fluorine⋯atom close contacts. The total percentages of fluorine⋯atom close contacts in compounds 1–3 were determined to be high at 47, 41.2 and 60.7%, respectively. As relatively few HSA studies on trifluoromethylated compounds have reported the percentages of individual atom⋯atom close contacts, we have also determined the percentages of atom⋯atom close contacts for 20 more trifluoromethylated compounds: the range of total fluorine⋯atom close contacts for these compounds was 20–60%. While these data are based on connections between similar molecules in a crystalline state, they also clearly suggest that a compound containing CF3 group(s) has the potential to make extensive intermolecular connections/close contacts with organic material. Thus a possible factor for the enhanced biological activity of a compound bearing CF3 group(s) could be the propensity of the CF3 group to form many close contacts, thereby aiding binding or interaction with a biological target.

Synthesis, identification and in vitro biological evaluation of some novel quinoline incorporated 1,3-thiazinan-4-one derivatives

The present study describes the synthesis of two new series of 3-hydroxy-N-(4-oxo-2-phenyl-1,3-thiazinan-3-yl)-8-(trifluoromethyl)quinoline-2-carboxamide derivatives (4a-j) and 3-((7-chloroquinolin-4-ylamino)methyl)-2-phenyl-1,3-thiazinan-4-one derivatives (5a-7j). All the compounds were synthesized in moderate to good yield by one-pot three component cyclo-condensation reaction. The newly synthesized compounds were characterized by FT-IR, ¹H, ¹³C NMR and elemental analysis. The compounds were screened for their in vitro antibacterial activity against a panel of pathogenic bacterial strains, antitubercular activity against Mycobacterium tuberculosis H₃₇Rv and also for their in vitro antimalarial activity against Plasmodium falciparum. Among the synthesized compounds two of them (4f and 5f) showed excellent antibacterial activity against C. tetani at 15.6μg/mL. Some of them exhibited excellent antitubercular (4f &5f) and good antimalarial (4f, 5f &6f) activity compared with the first line drugs.

Synthesis and antitubercular activity of new 1,3,4-oxadiazoles bearing pyridyl and thiazolyl scaffolds

In search of more potent and safe new antitubercular agents, here new 2-pyridinyl substituted thiazolyl-5-aryl-1,3,4-oxadiazoles (6a-o), have been designed and synthesized using thionicotinamide as a starting, following novel multistep synthetic route. An intermediate, pyridinyl substituted thiazolyl acid hydrazide (4) when condensed with benzoic acids/nicotinic acids (5a-o) in the presence of silica supported POCl3 yielded better to excellent yields of the title compounds. All the synthesized compounds (6a-o) and intermediate acid hydrazide (4) have been screened for their in vitro antitubercular activity against Mycobacterium tuberculosis H37Ra (MTB) and Mycobacterium bovis BCG. Amongst them, 6f, 6j, 6l and 6o have revealed promising activity against M. bovis BCG at concentrations less than 3μg/mL. These compounds have shown low cytotoxicity (CC50: >100μg/mL) towards four human cancer cell lines. Molecular docking study has also been performed against mycobacterial enoyl reductase (InhA) enzyme to gain an insight into the binding modes of these molecules and recorded good binding affinity. The ADME properties the title products have also been analyzed.

Ionic liquid-promoted one-pot synthesis of thiazole–imidazo[2,1-b][1,3,4]thiadiazole hybrids and their antitubercular activity

The anti-TB activity of new thiazole–imidazo[2,1-b][1,3,4]thiadiazoles, which are synthesized via one-pot synthesis, is comparable with that of standard drugs.

1,3,4-Trisubstituted pyrazole bearing a 4-(chromen-2-one) thiazole: synthesis, characterization and its biological studies

3-{2-[N′-(1,3-Disubstituted-1H-pyrazol-4-yl-methylene)-hydrazino]-thiazol-4-yl}-chromen-2-one compounds (10a–l) were synthesized, characterized and screened for their in vitro antimicrobial studies against various microorganisms. Most compounds were biologically active.