Acetohydroxyacid Synthase Inhibitors: N-Phthalyl-ʟ-valine Anilide and Related Compounds
Abstract The potency of ʟ-valine as an inhibitor of Zea mays acetohydroxyacid synthase (AHAS) is increased more than 80110-fold on conversion to its N-phthalyl anilide derivative which is active at 2 µᴍ. The ᴅ-valine, α-aminobutyric acid, isoleucine and phenylalanine analogs are 11- to 43-fold less potent, and similar N-phthalyl anilide derivatives of other branched-chain amino acids are essentially inactive. Full potency is retained on replacing the phthalimide moiety of the valine anilide with cyclohexane-1,2-dicarboximide or 1-cyclohexene-1.2-dicarboximide groups and partial activity with 4-cyclohexene-1,2-dicarboximide and methyl- or dimethylmaleimide groups. Inhibition of the enzyme and of root growth by the valine derivatives may result from binding at or near the site involved in feedback control of AHAS by ʟ-valine.