4'-Hydroxy-3-methoxyflavones with potent antipicornavirus activity.

4'-Hydroxy-3-methoxyflavones are natural compounds with known antiviral activities against picornaviruses such as poliomyelitis and rhinoviruses. In order to establish a structure-activity relationship a series of analogues were synthesized, and their antiviral activities and cytotoxicities were compared with those of flavones from natural origin. The 4'-hydroxyl and 3-methoxyl groups, a substitution in the 5 position and a polysubstituted A ring appeared to be essential requirements for a high activity. The most interesting compound was 4',7-dihydroxy-3-methoxy-5,6-dimethylflavone possessing in vitro TI99 values of greater than 1000 and greater than 200 against poliovirus type 1 and rhinovirus type 15, respectively. This compound was also active against other rhinovirus serotypes (2, 9, 14, 29, 39, 41, 59, 63, 70, 85, and 89) tested, having MIC50 values ranging from 0.016 to 0.5 micrograms/mL. Finally in contrast to quercetin it showed to be not mutagenic in concentrations up to 2.5 mg in the Ames test.