Structure-activity relationship of carboxin-related carboxamides as fungicide

Various carboxamides were synthesized and their structure-activity relationships were examined as fungicides. The fungicidal activity and spectrum depended on the aromatic ring and N-substituent at the amide moiety. Among them, N-(biphenyl-2-yl)-2-chloropyridine-3-carboxamide exhibited high activity against gray mold, and the corresponding 3-CF3-pyrazole-4-carboxamide exhibited higher activity. Moreover, it was found that compounds with hydrophobic branched alkyl groups at the ortho position of the N-phenyl group exhibited high and broad-spectrum fungicidal activity. The benzene ring of the N-phenyl group can be replaced with a thiophene ring, and optimization of the alkyl groups on the thiophene ring led to penthiopyrad (1); N-[2-(1,3-dimethylbutyl)-3-thienyl]-1-methyl-3-(trifluoromethyl)pyrazole-4-carboxamide, which proved to be very effective against various diseases.