Design, synthesis and antifungal evaluation of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety

A series of novel mandelic acid derivatives containing a 1,3,4-oxadiazothioether moiety were designed and synthesized. Bioassay results showed that some target compounds exhibited certain antifungal activity against six kinds of pathogenic fungi in vitro. Among the compounds, the EC50 values of T-41 against Gibberella saubinetii, Verticillium dahlia and Sclerotinia sclerotiorum were 31.0, 27.0 and 32.1 mu g/ml, respectively, and the EC50 value of T-14 against S. sclerotiorum was 14.7 mu g/ml. The antifungal activity against the resistant fungus S. sclerotiorum indicated that this series of target compounds may have the similar action modes or sites as the commercialized succinate dehydrogenase inhibitor carboxin. A morphological study with fluorescence microscope demonstrated that T-41 can significantly destroy the membrane integrity of G. saubinetii.