Acetolactate Synthase Inhibitors

Abstract

Acetolactate synthase (ALS; EC 4.6.3.8, also referred to acetohydroxy acid synthase; AHAS) is the first common enzyme in the biosynthetic pathway to the branched-chain amino acids; valine, leucine and isoleucine (Fig. 1). The pathway exists in plants and microorganisms such as bacteria, fungi and algae. ALS is the primary target site of action for at least four structurally distinct classes of herbicides including the sulfonylureas (SUs; LaRossa and Schloss 1984; Ray 1984), the imidazolinones (IMs; Shaner et al. 1984), the triazolopyrimidine sulfonamides (TPs; Subramanian and Gerwick 1989) and the pyrimidinylsalicylates (pyrimidinyl carboxy herbicides, PCs; Shimizu et al. 1994b), all of which have been successful in their development as commercial herbicides. The extremely good weed control activity achieved with these herbicides indicates that ALS is a very effective target site for herbicidal action. Deficiency of the pathway of branched-chain amino acids biosynthesis in mammals (Singh and Shaner 1995) shows us that it is the selective target between plants and mammals. ALS is therefore attractive for addressing a large number of goals of modern herbicide research.