Oxidation of 5-Hydroxypyrimidine Nucleosides to 5-Hydroxyhydantoin and Its α-Hydroxy-ketone Isomer
Bibliographic record
Abstract
The reaction of hydroxyl radicals with 2'-deoxycytidine (dCyd), as well as the decomposition of dCyd radical cations, leads to a complex mixture of oxidation products in aqueous aerated solutions. The oxidation of dCyd gives products with a relatively low oxidation potential that are highly susceptible to further oxidation, including 5-hydroxy-2'-deoxycytidine (5-oh-dCyd) and 5-hydroxy-2'-deoxyuridine (5-oh-dUrd). Previously, we showed that the oxidation of 2'-deoxyuridine (dUrd) involves the formation of dialuric acid and isodialuric acid intermediates, followed by ring contraction to N1-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-hydroxyhydantoin (5-oh-dHyd). In this work, we have examined the oxidation of 5-oh-dCyd and 5-oh-dUrd in greater detail. The oxidation of these substrates by Br2 led to a similar profile of intermediate and stable products indicating that the dialuric and isodialuric acid derivatives of dCyd largely undergo deamination before they transform into 5-oh-dHyd. Analysis of the final mixture of oxidation products by HPLC revealed the formation of two novel products. On the basis of NMR and MS, these products were identified as the diastereomers of N1-(2-deoxy-beta-D-erythro-pentofuranosyl)-5-hydroxyimidazolidine-2,5-dione (iso-4-oh-dHyd). These products arise from alpha-hydroxy-ketone isomerization of 5-oh-dHyd. The isomerization of 5-oh-dHyd to iso-4-oh-dHyd was reversible, and each diastereomer produced a specific diastereomer of the other structural isomer. The rate of isomerization was accelerated in going from pH 5 to pH 9, whereas all isomers decomposed at higher pH. In contrast, interconversion between each pair of diastereomers was minor. Thus, we conclude that the oxidation of 5-oh-dCyd or 5-oh-dUrd gives a mixture of four isomers of 5-oh-dHyd and iso-4-oh-dHyd as final products. The biological consequences of dCyd oxidation may ultimately depend on the effects of these products.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".