Synthetic analogs of phytoalexins. Synthesis and antifungal activity of potential free-radical scavengers

The mechanism of fungicidal action of phytoalexins has not yet been clearly established. Some authors have suggested that they can give rise to radicals upon irradiation with UV light; therefore, we have synthesized some stilbenes, chalcones, and isoflavans structurally related to phytoalexins, modified in order to obtain possible free-radical intermediates of different stability (either radical scavengers or chain propagating). They were tested in vitro and in vivo against some phytopathogenic fungi. It seems that steric hindrance due to tert-butyl groups has a negative effect, while allyl chains give rise to a compound with the widest spectrum of activity. Some commercial antioxidants were also tested; they have specific activity against some pathogens.