5-Cyanoimino-4-oxomethylene-4,5-dihydroimidazole and 5-cyanoamino-4-imidazolecarboxylic acid intermediates in nitrosative guanosine deamination: evidence from 18O-labeling experiments.
The nitrosative deaminations (37 degrees C, NaNO2, NaAc buffer, pH 3.7) of guanosine 1r in (18O)water (97.6%) and of [6-18O]-1r in normal water were studied. [6-(18)O]-1r was prepared from 2-amino-6-chloropurine riboside using adenosine deaminase. The reaction products xanthosine 3r and oxanosine 4r were separated by HPLC and characterized by LC/MS analysis and 13C NMR spectroscopy. The 18O-isotopic shifts on the 13C NMR signals were measured and allowed the identification of all isotopomers formed. The results show that oxanosine is formed via 5-cyanoimino-4-oxomethylene-4,5-dihydroimidazole, 5, and its 1,4-addition product 5-cyanoamino-4-imidazolecarboxylic acid, 6. This hydration of 5 to 6 leads to aromatization and greatly dominates over water addition to the cyanoimino group of 5 to form 5-guanidinyliden-4-oxomethylene-4,5-dihydroimidazole, 7. 5-Guanidinyl-4-imidazolecarboxylic acid, 8, the product of water addition to 6, is not involved.
Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211, USA.
Sundeep
S
Rayat
Papiya
P
Majumdar
Peter
P
Tipton
Rainer
R
Glaser
D004247:DNA / Q000737:chemistry / Q000378:metabolism; D003641:Deamination; D006151:Guanosine / Q000737:chemistry* / Q000378:metabolism*; D007093:Imidazoles / Q000737:chemistry* / Q000378:metabolism*; D007553:Isotope Labeling; D009573:Nitrites / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010103:Oxygen Isotopes; D011743:Pyrimidines / Q000737:chemistry / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization
D007093:Imidazoles; D009573:Nitrites; D010103:Oxygen Isotopes; D011743:Pyrimidines; D006151:Guanosine; D004247:DNA