Stacking-controlled phototransformations of the 5-fluorouracil residues in dinucleotide model compounds

Photochemistry of 5‐Fluorouracil Dideoxyribonucleoside Monophosphate

“…In other words, the similar kinetics argue that the relative quantum yields of CPD and photohydrate formation in dXpdX are similar to those of dUpdU and significantly different from those of dTpdT. It is interesting to note that the photochemistry of 5-fluorouracil appears to be independent of the length of the polynucleoside or the length of the chain connecting the 5-fluorouracil nucleobases, as all 5-fluorouracil systems studied to date form predominantly the photohydrates (9)(10)(11). This result is in contrast to that seen with thymine and, to a lesser extent, uracil, where the quantum yields for CPD formation increase with increasing sequence length.…”

“…In this article, we measure the UV photochemical rates of 5‐fluorouracil dideoxyribonucleoside monophosphate (dXpdX) with both absorption spectroscopy and mass spectrometry. UV irradiation of both the isolated 5‐fluorouracil nucleobase and the butyl‐linked dideoxyribonucleoside yields the respective photohydrate as the dominant photoproduct (9–11). This result is similar to that observed for the isolated thymine nucleobase, although the photochemistry of dTpdT is different, suggesting that the proximity of the other nucleobase can dramatically change the photochemistry.…”

Excited-State Structural Dynamics of 5-Fluorouracil

“…In both cases, the photohydrate was the dominant product. In those papers it was also noted that the cyclobutyl photodimer forms in the presence of an acetone sensitizer. , Thus, the photochemistry of 5-fluorouracil appears to be localized around the C 5 C 6 bond. Experiments are currently underway in our group to measure the photochemistry of the 5-fluorouracil dinucleotides.…”

“…Since no work has been done on the photochemistry of the 5-fluorouracil dinucleotides, the correlation between photochemistry and excited-state structural dynamics is still unclear. However, because 5-fluorouracil appears to preferentially form the photohydrate when in a butyl linked dimer, , there may be other factors beyond the excited-state structural dynamics that influence the photochemistry of these systems. For example, the substituent on C 5 may affect the stacking of the nucleobases in the dinucleotides, change the character of the electronic excited state in the nucleobase, or alter the excited-state curve-crossing geometries and states.…”