Design, synthesis and antifungal activity of pyrazole ester derivatives.

Pyrazole compounds have diverse structures and various biological activities, and thus play a significant role in the development of new pesticides. To continue our ongoing research on pyrazole compounds as antifungal active compounds, novel pyrazole ester compounds (A1-A10) containing a quinoline group were designed, synthesized, and evaluated for their antifungal activity. To our disappointment, their antifungal activity failed to meet our expectations. We changed our design concept and synthesized another series of pyrazole ester compounds containing 1-(4-chlorophenyl)-pyrazol-3-ol, then evaluated them for their antifungal activity. The results showed that the inhibitory activity of most compounds against the Pyricularia oryzae was higher than that of the other four test strains, Rhizoctonia solani, Botrytis cinerea, Fusarium graminearum and Alternaria solani. The results indicated that compounds B1, B2, B3, B4, B6, B7, B11, B12, B14, B15, and B16 showed excellent in vitro activities against Pyricularia oryzae (P. oryzae) with EC50 values from 1.79-10.89 mg L-1, superior to that of the commercial fungicides boscalid and hymexazol. In particular, the EC50 value of compound B16 against the P. oryzae was 1.79 mg L-1. Our research indicates that the typical pyrazole ester compound containing 1-(4-chlorophenyl)-pyrazol-3-ol can serve as a lead compound for antifungal activity.