Photochemical Ring Expansion of 4-Azidouracil: a Route to 5H-1,3,5-Triazepin-2,4-dione in the Nucleoside Series

Anti Regiospecificity in the Photosensitized Cycloaddition of 4-Tetrazolouracil Nucleoside†

The [2 + 2] photocycloaddition of natural pyrimidine nucleobases is devoid of regioselectivity. Although modified pyrimidines have been developed to selectively obtain syn-cyclobutane isomers, the targeted formation of anti-cyclobutane isomers has not been addressed yet. Herein, using NMR analyses and DFT calculations, we demonstrate that the acetone photosensitized excitation of the 4-tetrazolouracil motif in the nucleoside series specifically provides anti-cyclobutane photoproducts in 51% yield. In addition, the cis stereomer formation is preferred over the trans-cyclobutane formation (71:29).

Three-component and one-pot synthesis of 3-aryl-2,4-diselenoxo-1,3,5-triazepane-6,7-diones

A simple, one-pot synthesis of six 3-aryl-2,4-diselenoxo-1,3,5-triazepane-6,7-diones has been achieved in moderate to good yields via a three-component condensation of variously substituted anilines, oxalyl chloride, and two molecules of potassium selenocyanate in acetone at room temperature.

Sensitized photochemistry of di(4-tetrazolouracil) dinucleoside monophosphate as a route to dicytosine cyclobutane photoproduct precursors

The DNA cis-syn cyclobutane photoproduct formed between two adjacent cytosine residues is highly mutagenic and responsible for the tandem CC to TT transition. However, its instability has prevented its in vitro study, so far. With a view to prepare oligodeoxynucleotides containing the CC cyclobutane lesion, we have synthesized in good yield a ditetrazolouracil cyclobutane dinucleotide photoproduct as a stable precursor of this photoproduct. Our approach also overcomes the low photochemical reactivity of the cytosine-cytosine deoxydinucleoside monophosphate.

Unraveling the photochemistry of the 5-azido-2'-deoxyuridine photoaffinity label

UV irradiation of 5-azido-2'-deoxyuridine in water provides up to seven products. All likely result from a pivotal azirene, formed by the intramolecular rearrangement of the initially formed nitrene, that undergoes nucleophilic addition at its C5 position. This study strongly suggests that only nucleophilic amino acid residues in close proximity are cross-linkable in photolabeling experiments by using the 5-azidouracil photophore.