silica-bonded n-propyldiethylenetriamine sulfamic acid (sbpdsa) was found as an efficient solid acid for the synthesis of coumarins. coumarin derivatives were obtained via the pechmann condensation reaction of phenols and β-keto-esters at 80 oc under solvent-free conditions. also, biscoumarins were obtained via the condensation of aldehydes and 4-hydroxycoumarin in water at reflux conditions. t...

The enzyme tyrosinase is known to be a multifunctional copper-containing enzyme from the oxidase superfamily, which is the key protein involved in the biosynthesis of the large biological pigment, melanin. The enzyme catalyzes two distinct reactions of melanin biosynthesis, the hydroxylation of a monophenol and the conversion of an o-diphenol to the corresponding o-quinone. Inhibitors of this p...