Acetohydroxyacid synthase inhibitors: N-phthalyl-L-valine anilide and related compounds

The potency of L-valine as an inhibitor of Zea mays acetohydroxyacid synthase (AHAS) is increased more than 8000-fold on conversion to its N-phthalyl anilide derivative which is active at 2 microM. The D-valine, alpha-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 L-valine.