title: Synthesis and evaluation of hydroxyazolopyrimidines as herbicides; the generation of amitrole in planta.
abstract: BACKGROUND
  Exploiting novel herbicidal modes of action is an important method to overcome the challenges faced by increasing resistance and regulatory pressure on existing commercial herbicides. Recent reports of inhibitors of enzymes in the non-mevalonate pathway of isoprenoid biosynthesis led to the design of a novel class of azolopyrimidines which were assessed for their herbicidal activity. Studies were also undertaken to determine the mode of action responsible for the observed herbicidal activity.
  
  
  RESULTS
  In total, 30 novel azolopyrimidines were synthesised and their structures were unambiguously determined by1H NMR, mass spectroscopy and X-ray crystallographic analysis. The herbicidal activity of this new chemical class was assessed against six common weed species, with compounds from this series displaying bleaching symptomology in post-emergence tests. A structure-activity relationship for the novel compounds was determined, which showed that only those belonging to the hydroxytriazolopyrimidine subclass displayed significant herbicidal activity. Observed similarities between the bleaching symptomology displayed by these herbicides and amitrole suggested that hydroxytriazolopyrimidines could be acting as elaborate propesticides of amitrole, and this was subsequently demonstrated in plant metabolism studies using Amaranthus retroflexus. It was shown that selected hydroxytriazolopyrimidines that displayed promising herbicidal activity generated amitrole, with peak concentrations of amitrole generally being observed 1 day after application. Additionally, the herbicidal activity of selected compounds was profiled against tobacco plants engineered to overexpress 4-diphosphocytidyl-2C-methyl-d-erythritol synthase (IspD) or lycopene β-cyclase, and the results suggested that, where significant herbicidal activity was observed, inhibition of IspD was not responsible for the activity. Tobacco plants overexpressing lycopene β-cyclase showed tolerance to amitrole and the two most herbicidally active triazolopyrimidines.
  
  
  CONCLUSIONS
  Inhibition of IspD leading to herbicidal activity has been ruled out as the mode of action for the hydroxytriazolopyrimidine class of herbicides. Additionally, tobacco plants overexpressing lycopene β-cyclase showed tolerance to amitrole, which indicates that this is the main herbicidal mode of action for amitrole. Results from the metabolic fate study of selected hydroxytriazolopyrimidines suggested that the herbicidal activity displayed by these compounds is due to amitrole production, which was confirmed when tobacco plants overexpressing lycopene β-cyclase also showed tolerance towards two triazolopyrimidines from this study. © 2016 Society of Chemical Industry.
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: John M
authors.initials: JM
authors.lastname: Clough
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Richard P
authors.initials: RP
authors.lastname: Dale
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Barry
authors.initials: B
authors.lastname: Elsdon
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Hawkes
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Bridget V
authors.initials: BV
authors.lastname: Hogg
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Anushka
authors.initials: A
authors.lastname: Howell
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Kloer
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Karine
authors.initials: K
authors.lastname: Lecoq
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Matthew Mw
authors.initials: MM
authors.lastname: McLachlan
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Phillip J
authors.initials: PJ
authors.lastname: Milnes
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK. tim.o_riordan@syngenta.com.
authors.forename: Timothy Jc
authors.initials: TJ
authors.lastname: O'Riordan
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Saranga
authors.initials: S
authors.lastname: Ranasinghe
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Shanahan
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Karen D
authors.initials: KD
authors.lastname: Sumner
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berks, UK.
authors.forename: Shanaaz
authors.initials: S
authors.lastname: Tayab
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000037:antagonists & inhibitors / Q000235:genetics; D027721:Amaranthus / Q000187:drug effects; D000640:Amitrole / Q000493:pharmacokinetics / Q000494:pharmacology; D060326:Chemistry Techniques, Synthetic; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000494:pharmacology; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D006540:Herbicides / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D019753:Intramolecular Lyases / Q000235:genetics; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000235:genetics; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics; D057685:Plant Weeds / Q000187:drug effects; D030821:Plants, Genetically Modified; D011743:Pyrimidines / Q000737:chemistry; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000187:drug effects / Q000235:genetics
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D006540:Herbicides; D009097:Multienzyme Complexes; D011743:Pyrimidines; D010088:Oxidoreductases; C522017:IspD protein, E coli; D019747:Aldose-Ketose Isomerases; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase; D000640:Amitrole
keywords: amitrole; herbicides; metabolism; mode of action