The structure-antifungal activity relationship of 5,7-dihydroxyflavonoids against Penicillium italicum

To evaluate the structure-activity relationship of 5,7-dihydroxyflavonoids against P. italicum, we tested the antifungal activity of 23 selected 5,7-dihydroxyflavonoids against spore germination of P. italicum, and the effects of hydroxyl group, hydrogenation, methylation and glycosylation on the antifungal activity are explored. C-4'-OH and C-3-OH are active groups for the 5,7-dihydroxyflavonoids against P. italicum. We find that hydrogenation of the C2/C3 bond decreases the antifungal activity of 5,7-dihydroxyflavonoids. Antifungal activity of 5,7-dihydroxyflavonoids against P. italicum was affected by the conjugation site of glycosylation and the class of sugar moiety. The correlation between antifungal activity and the inhibition of respiration of 5,7-dihydroxyflavonoids was further evaluated. We find no significant relationship among the IC50 of 5,7-dihydroxyflavonoids on spore germination and on respiration. Some 5,7-dihydroxyflavonoids even enhance the respiration of P. italicum. This indicate respiration is not the only target for 5,7-dihydroxyflavonoids against P. italicum.