Structure-Activity Relationship of Dialkoxychalcones to Combat Fish Pathogen Saprolegnia australis

To investigate the anti-Saprolegnia activities of chalconic compounds, nine dialkoxychalcones 2⁻10, along with their key building block 2',4'-dihydroxychalcone 1, were evaluated for their potential oomycide activities against Saprolegnia australis strains. The synthesis afforded a series of O-alkylated derivatives with typical chalcone skeletons. Compounds 4⁻10 were reported for the first time. Interestingly, analogue 8 with the new scaffold demonstrated remarkable in vitro growth-inhibitory activities against Saprolegnia strains, displaying greater anti-oomycete potency than the standard drugs used in the assay, namely fluconazole and bronopol. In contrast, a dramatic loss of activity was observed for O-alkylated derivatives 2, 3, 6, and 7. These findings have highlighted the therapeutic potential of the natural compound 1 scaffold to be exploitable as a drug lead with specific activity against various Saprolegnia strains.