Synthesis and fungicidal activities of positional isomers of the -thienylcarboxamide.

To investigate the effects of bioisosteric replacement of the phenyl group with the thienyl group, -phenylcarboxamide and three regioisomers of -(substituted-thienyl)carboxamide were synthesized. The inhibitory activity on the succinate dehydrogenase prepared from the gray mold as well as the fungicidal activity against were evaluated. Two isomers, -(2-substituted-3-thienyl)carboxamide and -(4-substituted-3-thienyl)carboxamide exhibited the same level of activity as the phenyl derivative, whereas -(3-substituted-2-thienyl)carboxamide exhibited lower activity than the phenyl derivative, suggesting that the 2-substituted-3-thienyl and 4-substituted-3-thienyl groups functioned as bioisosteres of the phenyl group in -phenylcarboxamide, but the other did not.