Synthesis and Biological Activity of Quaternary Quinolinium Salts: A Review

Heterocyclic chemistry is the only branch of chemistry that has applications in varied areas such as dyes, photosensitizers, coordination compounds, polymeric materials, biological, and many other fields. Quinoline and its derivatives have always engrossed both synthetic chemists and biologists because of their diverse chemical and pharmacological properties as these ring systems can be easily found in various natural products, especially in alkaloids. Among alkaloids, quinoline derivatives i.e. quinolinium salts have attracted much attention nowadays owing to their diverse biological profile such as antimicrobial, antitumor, antifungal, hypotensive, anti-HIV, analgesics and anti-inflammatory, etc. Quinoline and its analogs have recently been examined for their modes of function in the inhibition of tyrosine kinases, proteasome, tubulin polymerization, topoisomerase, and DNA repair. These observations have been guiding scientists for the expansion of new quinoline derivatives with improved and varied biological activities. Quinolinium salts have immense possibilities and scope to investigate these compounds as potential drug candidates. Therefore, we shall present a concise compilation of this work to aid in present knowledge and to help researchers explore an interesting quinoline class having medicinal potential.

External-photocatalyst-free visible-light-mediated aerobic oxidation and 1,4-bisfunctionalization of N-alkyl isoquinolinium salts

Visible-light-induced aerobic alternate transformations of N-alkyl isoquinolinium/quinolinium salts in the absence of any external photocatalyst have been developed.

Synthesis of pyrrolo[1,2-a]quinolines by formal 1,3-dipolar cycloaddition reactions of quinolinium salts

Quinolinium salts, Q+-CH2-CO2Me Br− and Q+-CH2-CONMe2 Br− (where Q = quinoline), were prepared from quinolines. Deprotonation of these salts with triethylamine promoted the reaction of the resulting quinolinium ylides (formally azomethine ylides) with electron-poor alkenes by conjugate addition followed by cyclization or by [3 + 2] dipolar cycloaddition. The pyrroloquinoline products were formed as single regio- and stereoisomers. These could be converted to other derivatives by Suzuki–Miyaura coupling, reduction or oxidation reactions.