Crude peroxidase from onion solid waste as a tool for organic synthesis. Part III: synthesis of tetracyclic heterocycles (coumestans and benzofuroquinolinones)

In the present study the biocatalytic activity of a crude onion peroxidase extract on the reaction between catechol and heterocyclic 1,3-dicarbonyl compounds is investigated. The crude enzyme preparation promotes effectively the reaction between catechol and 4-hydroxycoumarin, 4-hydroxy-1-methyl-2-quinolinone and 2,4-quinolinediol to afford the corresponding coumestans and benzofuroquinolinones in satisfactory yields. The products of the reaction are fully characterized spectroscopically and are found to possess potent antioxidant activity as evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power (FRAP), and luminol-induced chemiluminescence assays.