Vinylogous sulfonylureas: a new class of acetohydroxyacid synthase inhibitors incorporating a large bridging moiety

Several acrylic acid derivatives incorporating elements of sulfonylurea structure around a central vinylogous core were synthesized and found to be moderate inhibitors of the enzyme, acetohydroxyacid synthase (AHAS). Some compounds showed post-emergence herbicidal activity against mustard. Biological activity was found to be markedly influenced by the nature of the 2-arylcarbam oyl group. When this group contained a phenyl ring the compounds were inactive. A 4,6-dim ethoxypyrim idin-2-ylcarbamoyl function resulted in the best activity but this activity was highly dependent on the nature of the 4,6-substituents on the pyrimidine ring, with 4,6-dim ethylpyrim idines showing very little activity. The structures of the most active compound, ethyl 3-(2-chlorophenyl)sulfonylam ino-3-m ethylthio-2-[(4,6-dim ethoxypyrim idin- 2-yl)carbam oyl]acrylate, and an inactive analogue, 4,6-dimethylpyrim idin-2-yl-3-(2-chlorophenyl) sulfonylam ino-3-m ethylthio-2-cyanoacrylate, were determined by X-ray crystallography. The resulting structures showed several conformational differences which may play an important role in inhibitor binding to AHAS and the resultant herbicidal activity