Rayat S, Majumdar P, Tipton P, Glaser R. 5-Cyanoimino-4-oxomethylene-4,5-dihydroimidazole and 5-Cyanoamino-4-imidazolecarboxylic Acid Intermediates in Nitrosative Guanosine Deamination: Evidence from 18O-Labeling Experiments.
J Am Chem Soc 2004;
126:9960-9. [PMID:
15303870 DOI:
10.1021/ja049835q]
[Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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.
Collapse