Hemisynthesis of all the O-monomethylated analogues of quercetin including the major metabolites, through selective protection of phenolic functions

A new methodology for the hemisynthesis of all the five O-monomethylated analogues of quercetin (3′-O-methylquercetin (isorhamnetin), 4′-O-methylquercetin (tamarixetin), 3-O-methylquercetin, 5-O-methylquercetin (azaleatin) and 7-O-methylquercetin (rhamnetin)) through sequential protection of the different phenolic functions of quercetin is reported.