Oxanosine Is a Substrate of Adenosine Deaminase. Implications for the Quest for a Toxicological Marker for Nitrosation Activity
Oxanosine 3r, 5-amino-3-β-(D-ribofuranosyl)-3H-imidazo[4,5-d][1,3] oxazine-7-one, was isolated as a novel nucleoside antibiotic in 1981 from Streptomyces capreolus MG265-CF3. Oxanosine became relevant in toxicology in 1996 with the discovery that it is formed in nitrosative guanosine deamination. As part of studies of the mechanism of oxanosine formation, the synthesis was attempted of [7-18O] oxanosine by enzymatic 16O/18O-exchange with adenosine deaminase (ADA) in analogy to the synthesis of [6-18O]guanosine from 2-amino-6-chloropurine. Unexpectedly, it was discovered that the incubation of oxanosine 3r with ADA in sodium phosphate buffer (pH = 7.4) results in 1-β-(D-ribofuranosyl)-5- ureido-1H-imidazole-4-carboxylic acid 4r. The reaction of the 2'-deoxyribose derivative 3d forms 4d in analogy. The reaction products were separated by preparative RP-HPLC and characterized by LC/MS and MS/MS analyses and UV/vis and NMR spectroscopy, and NMR assignments were corroborated by GIAO and GIAO-PCM calculations. Reaction in H218O leads to 18O-incorporation at C7. The hydrolysis of 3 to 4 can be rationalized on the basis of the known mode of action of ADA, and an explanation is provided for ADA's accomplishment of the "usual" substitution at C6 of adenosine (addition to the exocyclic bond) and the "lactone hydrolysis" of oxanosine (addition to the endocyclic double bond). The Michaelis-Men ten constant of Km = 1.0 (±0.2) mM was measured for oxanosine. Implications are discussed for studies of nitrosative deamination of nucleosides, nucleotides, and oligonucleotides.
P. S. Majumdar et al., "Oxanosine Is a Substrate of Adenosine Deaminase. Implications for the Quest for a Toxicological Marker for Nitrosation Activity," Chemical Research in Toxicology, vol. 18, no. 12, pp. 1830-1841, American Chemical Society (ACS), Nov 2005.
The definitive version is available at https://doi.org/10.1021/tx050232h
Keywords and Phrases
1 beta (dextro ribofuranosyl) 5 ureido 1h imidazole 4 carboxylic acid; 2 amino 6 chloropurine; 2' deoxyribose derivative; 5 amino 3 beta (dextro ribofuranosyl) 3h imidazo[4,5 d]oxazin 7 one; adenosine; adenosine deaminase; antibiotic agent; buffer; carboxylic acid derivative; chemical compound; deoxyribose; guanosine; lactone; marker; nucleoside derivative; oxanosine; oxygen; oxygen 18; purine derivative; reaction product; sodium dihydrogen phosphate; unclassified drug; addition reaction; analytic method; calculation; deamination; gauge independent atomic orbital method; hydrolysis; liquid chromatography; mass spectrometry; Michaelis constant; model; nitrosation; nitrosative deamination; nucleotide metabolism; oxygen exchange; oxygen transport; polarized continuum model; reversed phase high performance liquid chromatography; Streptomyces; Streptomyces capreolus MG265 CF3; toxicology; Adenosine; Adenosine Deaminase; Biological Markers; Computer Simulation; Deoxyribonucleosides; Inosine; Magnetic Resonance Spectroscopy; Mass Spectrometry; Models; Molecular; Molecular Structure; Nitrosation; Ribonucleosides; Saccharothrix mutabilis subsp. capreolus; Streptomyces
International Standard Serial Number (ISSN)
Article - Journal
© 2005 American Chemical Society (ACS), All rights reserved.
01 Nov 2005