Therapeutic significance of quinolines: a patent review (2013-2015).

INTRODUCTION: Quinoline is a versatile bicyclic heterocyclic scaffold with immense therapeutic potential. Some of the compounds containing quinoline nucleus are agents of choice for the treatment of various ailments, particularly cancer and malaria. Furthermore, several quinoline derivatives exhibit a broad spectrum of antimicrobial, anti-inflammatory, and antidiabetic activities, quite a few of which are under clinical investigation to combat potentially lethal diseases/disorders. AREAS COVERED: The present review summarizes inventions developed towards finding new chemotherapeutic agents based on the quinoline skeleton. It presents an outline of patents filed between 2013 and 2015, relating to the anticancer, antimicrobial, anti-inflammatory and other biological activities exhibited by quinoline derivatives. EXPERT OPINION: Several molecules containing quinoline skeleton are clinically significant drugs, extensively used for the treatment of various human diseases/disorders. The clinical success of some of these compounds and the versatile character of the quinoline nucleus attracted medicinal chemists in the development of newer chemotherapeutic agents. The considerably high number of patents filed in a relatively short period of time indicates the increasing importance of this pharmacophore. The development of facile synthetic strategies is anticipated to facilitate the generation of chemical libraries that could serve as a source of new chemical entities.

Synthesis and Biological Evaluation of 1,2,3-triazole tethered Pyrazoline and Chalcone Derivatives.

A series of pyrazoline derivatives and corresponding chalcone intermediates with substituents same as combretastatin-A4(CA-4) conjugated with triazole nucleus has been synthesized and evaluated for their anticancer potential. Sulphorhodamine B(SRB) assay indicated compound 12c to be the most active compound from the series with GI50 value of 6.7 µm against the human liver carcinoma cell line HepG2. Interestingly, the intermediate 11c exhibited more promising cytotoxicity demonstrating GI50 value of 1.3 µm against the prostate cancer cell line DU145. Compounds 11c and 12c caused accumulation of cells in G2/M phase and inhibited tubulin polymerization. Furthermore, these compounds reduce the mitochondrial membrane potential and activate caspases 3 and 9, thereby indicating their ability to trigger apoptosis.

Recent developments towards podophyllotoxin congeners as potential apoptosis inducers.

Podophyllotoxin, a lignan extracted from rhizomes of Podophyllum species, is a well established lead in the development of new chemical agents for the treatment of cancer. Its semi-synthetic variant, etoposide is an anticancer drug which inhibits DNA topoisomerase II causing cell cycle arrest in the S the phase. Its clinical success and intriguing mode of action made it a much sought after skeleton for the development of better antitumor agents. Modifications were made at several positions of its skeleton with the aim to either improve its potency or to overcome drug resistance. In recent years, the structurally modified podophyllotoxins have been investigated for their apoptosis inducing ability. Although numerous reviews emphasized the occurrence, synthesis and applications of podophyllotoxins, the recent progress towards development of structurally modified podophyllotoxins possessing apoptosis inducing ability has not been previously reviewed. Therefore the present review focuses on the studies carried out in the design and synthesis of new podophyllotoxin derivatives and their evaluation as apoptosis inducers.

Regioselective synthesis, antimicrobial evaluation and theoretical studies of 2-styryl quinolines.

2-Styryl quinolines (9a-l) have been synthesized regioselectively from 2-methyl-quinoline by using NaOAc in water acetic acid binary solvents and evaluated for their antibacterial activity against both Gram-positive and Gram-negative strains. Among these, the compounds 12 and 8 were found to be active against both bacterial strains. Compounds 9b, 9f, 9g, 9i, 9j and 9k were the most active among the series exhibiting MIC values ranging between 1.9 and 31.2 µg ml(-1) against different bacterial strains. Compounds 9j and 9k were found to be as potent as the standard drug ciprofloxacin against Micrococcus luteus, Klebsiella planticola and Staphylococcus aureus. In addition, the compounds showed bactericidal activity; compound 9j was found to be better than ciprofloxacin, with an MBC value of 0.9 µg ml(-1) against both M. luteus and K. planticola. The compounds also inhibited biofilm formation, and compound 9j was found to be equipotent to erythromycin against M. luteus and S. aureus MLS16. Further, theoretical studies such as those on druggable properties and PMI plot have been carried out.

Anti-tubercular agents. Part 8: synthesis, antibacterial and antitubercular activity of 5-nitrofuran based 1,2,3-triazoles.

A series of 5-nitrofuran-triazole conjugates were synthesized and evaluated for their antimicrobial activity against both Gram-positive and Gram-negative bacterial strains. All the compounds exhibited promising inhibition towards Gram-positive pathogenic strains, while mild inhibitory effects were observed towards Gram-negative bacterial strains. Some of the compounds 8a, 8b, 8e, 8f, 8h are most active among the series exhibiting MIC value of 1.17 µg/ml against different bacterial strains. The bactericidal activity is found to be in accordance with the bacterial growth inhibition data. Compound 8e was found to be equipotent to the standard drug Ciprofloxacin displaying MBC value of 1.17 µg/ml against the bacterial strain Bacillus subtilis. The compounds have also demonstrated promising antibacterial activity against the resistant strain MRSA and were found to be effective inhibitors of biofilm formation. The compound 8b exhibited excellent anti-biofilm activity with IC50 value as low as 0.8 µg/ml. These conjugates were also screened for antitubercular activity against Mycobacterium tuberculosis H37Rv strain. Compound 8e showed promising antitubercular activity with MIC value of 0.25 µg/ml. Most of these compounds are less toxic to normal mammalian cells than the widely used antibacterial drug Ciprofloxacin.