Discovery of novel obovatol-based phenazine analogs as potential antifungal agents: synthesis and biological evaluation in vitro

To explore candidate fungicides from plant secondary metabolites, 16 novel obovatol-type phenazine derivatives were semi-synthesized from obovatol isolated from the leaves of Magnolia obovata Thunb. The antifungal activity of synthesized compounds was investigated in vitro against four phytopathogenic fungi using the spore germination method. The bioassay results showed that eight derivatives ( 8b , 8g , 8h – k , 8i′ , and 8k′ ) exhibited better antifungal activity against Fusarium solani than two positive controls, especially compounds 8b (IC 50  = 64.61 μg mL −1 ) and 8i′ (IC 50  = 79.97 μg mL −1 ) showed pronounced inhibition of spore germination activity against F. solani . They could be used as lead compounds for further structural optimization. Additionally, the preliminary structure-activity relationships (SARs) illustrated that the introduction of a benzene ring monosubstituted with electron-withdrawing groups into the obovatol scaffold could lead to potentially antifungal compounds.