The maize benzoxazinone DIMBOA reacts with glutathione and other thiols to form spirocyclic adducts

Phytochemistry
David P DixonPatrick G Steel

Abstract

Maize, wheat and other grasses synthesise large quantities of benzoxazinones and their glucosides, which act as antifeedant and allelopathic agents. These activities are probably due to the electrophilic nature of the aglycones, however, the mechanism of their action is unclear. In biological systems, glutathione (GSH) is the major electrophile-reactive compound so the reaction of the major maize benzoxazinone DIMBOA with GSH was studied. GSH reacts with DIMBOA to form eight isomeric mono-conjugates and eight isomeric di-conjugates. Through NMR studies with the model thiol 2-mercaptoethanol, these were structurally elucidated as unusual spirocycles. Similar reactivity was observed with proteins, with cysteinyl thiols being modified by DIMBOA. The thioether bonds formed were stable and not easily reduced to the parent thiol. DIMBOA can therefore readily deplete GSH levels and irreversibly inactivate enzymes with active-site cysteine residues, with clear implications for potentially toxic effects when young grasses are ingested, whether by insect pests or humans.

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Citations

Jul 12, 2014·Molecular Plant-microbe Interactions : MPMI·Vessela Atanasova-PenichonFlorence Richard-Forget
Aug 29, 2014·Biological Reviews of the Cambridge Philosophical Society·Stefan PentzoldSøren Bak
Feb 11, 2015·The New Phytologist·Anna PiaseckaPaweł Bednarek
Dec 10, 2016·Phytochemistry Reviews : Proceedings of the Phytochemical Society of Europe·Felipe C WoutersDaniel G Vassão
Dec 5, 2018·Frontiers in Plant Science·David P Dixon, Robert Edwards
Oct 24, 2018·Frontiers in Plant Science·Daniel Giddings VassãoJonathan Gershenzon

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