Coumarins: New Synthetic Approaches and New Pharmacological Applications

The articles included in this Research Topic illustrate how coumarins can function as highly sensitive and selective fluorophores, and also present new synthetic methods to access coumarin derivatives with biological activities.Coumarin has frequently been used as fluorophore because of its π-π conjugated system. Wang et al (2021) report the evaluation of the applicability of various superoxide anion sensors that were designed and synthesized using either coumarin or chromone as the fluorophores. The authors reported the preference of both types of probes for various reactive oxygen species (ROS), and studies on their detection selectivity of redox-based O2 •− , thus obtaining very selective redox-based O2 •− probes. (Wang et al, 2021) Continuous attempts to develop new synthetic methods for the coumarin core have been reported, including the use of new catalysts, green reaction conditions, and the application of more recent techniques such as microwaves and ultrasounds. Indeed, Sing et al (2022) report a short and efficient multicomponent sequence for synthesizing fused novel polyheterocyclic chromeno spiro-pyrrolidine oxindoles via 1,3dipolar cycloaddition reaction mediated by reactive azomethine ylides and catalyzed by the Graphene Oxide (GO). Their methodology proved to be both greener and labour-saving as the products were isolated by simple filtration without the use of any chromatographic techniques.Furthermore, Alshabanah et al (2022) report a three-component reaction for the synthesis of novel 3-heteroaryl-coumarin utilizing acetylcoumarin synthon under ultrasonic irradiation and chitosan-grafted poly(vinylpyridine) as an eco-friendly catalyst. This facile and efficient procedure generated compounds with a thiazole ring linked to the coumarin moiety, including three new compounds that showed promising anticancer activity against HEPG2-1 tumoral cells.Finally, Balewski et al (2021) describe the incorporation of a metal ion into coumarin derivatives. Accordingly, some of these new ligands have been found to display promising antioxidant, antitumor, or antibacterial activities compared to coumarin-based ligands.In conclusion, this research topic shows the importance and the versatility of the coumarin core in applications of organic and medicinal chemistry.