Phenazine-1-carboxylic acid (EC50 = 27.87 μg/mL). The preliminary structure–activity relationship (SAR) results suggested that introducing methyl, halogen, or methoxy at the ortho-position of R1 and the para-position of R2 can endow the final structure with excellent antifungal activity against M. oryzae. The current results provide useful data for developing phenylthiazole derivatives as new fungicides