Lipophilicity-antifungal activity relationships for some isoflavonoid phytoalexins

The octanol/water partition coefficients of 18 isoflavonoid phytoalexins have been determined by reversed-phase HPLC and/or calculated by the use of Hansch hydrophobic parameters: The values obtained are in the range 1.5-4.2. From a study of the relationship between these data and the antifungal activity on Aphanomyces euteiches and Fusarium solani f.sp. cucurbitae reported by Van Etten, it appears that within groups of compounds of similar structure an increase in lipophilicity correlates positively with increased antifungal activity, whereas a general correlation for the whole class of isoflavonoid phytoalexins was not found. On the other hand, correlations with some other structural factors, such as the presence of a phenolic OH or benzylic hydrogen atoms, seem possible.