Chemical Methods Towards the Investigation of Multiple Herbicide Resistance in Black Grass (Alopecurus myosuroides)

Abstract

As the world population rises and the availability of land for cultivation decreases, there is an ever-growing demand on food production. However, the persistent use of herbicides in order to sustain food production has resulted in the emergence of resistance. The most serious form of resistance is multiple herbicide resistance (MHR) in which plants become resistant to all herbicides regardless of their mode of action.
Previous work involving the weed black grass identified a key glutathione S-transferase (GST), AmGSTF1, involved in the development of MHR. Small molecule inhibitors of the benzoxadiazole motif have been shown to disrupt the function of this enzyme and consequently suppress resistance. This work describes the synthesis of 4-substituted-7-nitrobenzofurazan derivatives and structurally related 6-halopurine analogues to investigate SAR. Assessment of these compounds through in vitro and in vivo studies revealed that alkoxy and thiol leaving groups were preferred for activity in the benzofurazan series, whilst 8-substituted-6-halopurine analogues were favoured in the purine series. However, no significant enhancement in activity over the parent structures was observed with these pharmacophores.
Further studies identified a new class of small molecule inhibitors through ligand fishing in which AmGSTF1 was immobilised on a streptactin column and washed with a cocktail of inhibitors. This method revealed flavonoid compounds to be potent binders of AmGSTF1. The subsequent synthesis and SAR evaluation of flavones highlighted 5,7-dihydroxyflavone as a key pharmacophore. Additional work revealed a fatty acid quercetin derivative to be a potent inhibitor of AmGSTF1, and was subsequently shown to be capable of synergising the effects of herbicides in MHR black grass.