title: Formation of fluorophores from the kynurenine pathway metabolite N-formylkynurenine and cyclic amines involves transamidation and carbon-carbon bond formation at the 2-position of the amine.
abstract: BACKGROUND
  Tryptophan catabolism along the kynurenine pathway is associated with a number of pathologies including cataract formation and cancer. Whilst the chemical reactions of kynurenine are well studied, less is known about the reactivity of its precursor N-formylkynurenine (NFK). We previously reported the generation of a strong fluorophore in an aqueous reaction of NFK with piperidine, and herein we describe its structure and mechanism of formation.
  
  
  METHODS
  Compounds were identified using NMR, mass and UV spectroscopic techniques. The products from the reaction of amines with amino acids were quantified using HPLC-MS.
  
  
  RESULTS
  The novel fluorophore was identified as a tetrahydroquinolone adduct (PIP-THQ), where piperidine is N-formylated and attached at its 2-position to the quinolone. NFK is initially deaminated to generate an unsaturated enone, which forms an adduct with piperidine and is subsequently converted into the fluorophore. Testing of a variety of other secondary amines showed that only cyclic amines unsubstituted at both positions adjacent to nitrogen could form fluorophores efficiently. The amino acids tryptophan and kynurenine, which lack the formamide group do not form such fluorophores.
  
  
  CONCLUSIONS
  NFK forms fluorophores in a not previously published reaction with cyclic amines.
  
  
  CONCLUSIONS
  Our study is the first to provide evidence for concurrent transamidation and substitution at the 2-position of a cyclic amine occurring under moderately-heated aqueous conditions with no added catalysts. The high reactivity of NFK demonstrated here could result in formation of biologically relevant metabolites yet to be characterised.
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Petr
authors.initials: P
authors.lastname: Tomek
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Brian D
authors.initials: BD
authors.lastname: Palmer
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Jackie D
authors.initials: JD
authors.lastname: Kendall
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand.
authors.forename: Jack U
authors.initials: JU
authors.lastname: Flanagan
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, School of Medicine, University of Auckland, Auckland, New Zealand. Electronic address: l.ching@auckland.ac.nz.
authors.forename: Lai-Ming
authors.initials: LM
authors.lastname: Ching
mesh_terms: D000588:Amines / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000378:metabolism*; D007737:Kynurenine / Q000031:analogs & derivatives* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D014364:Tryptophan / Q000378:metabolism*
chemical_list: D000588:Amines; D005456:Fluorescent Dyes; C007772:N'-formylkynurenine; D007737:Kynurenine; D014364:Tryptophan
keywords: Fluorophore; Indoleamine 2,3-dioxygenase; N-formylkynurenine; Piperidine; Transamidation; Tryptophan catabolism