Photochemical reactions of 5-fluorouracil and 5-fluoro-2′-deoxyuridine with N α-acetyl- L-tryptophan N-ethylamide in aqueous solution

• Published in: Journal of photochemistry and photobiology. B, Biology Vol. 43; no. 1; pp. 66 - 72
• Main Author: Celewicz, Lech
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-04-1998
• Subjects: 5-Fluoro-2′-deoxyuridine; 5-Fluorouracil; N-ethylamide; Nα-acetyl-1-tryptophan; Photocoupling reactions; N-ethylamide; 5-Fluoro-2′-deoxyuridine; N α-acetyl-1-tryptophan; 5-Fluorouracil; Photocoupling reactions
• ISSN: 1011-1344; 1873-2682
• DOI: 10.1016/S1011-1344(98)00090-6

Irradiation of 5-fluorouracil (
1) and 5-fluoro-2′-deoxyuridine (
2) with
N
α-acetyl-
L-tryptophan
N-ethylamide (
5) in aqueous buffered (pH
7) solutions led to
N
α-acetyl-2-(uracil-5-yl) tryptophan
N-ethylamide (
6) and
N
α-acetyl-2-[l-(2-deoxy-
β-l)
erythro-pentofuranosyl)uracil-5-yl] tryptophan
N-ethylamide (
7), respectively, as the main photoproducts. In addition, compounds
6 and
7 were synthesized by photochemical coupling of 5-bromouracil (
3) and 5-bromo-2′-deoxyuridine (
4), respectively, with
5. The formation of cross-links between 5-fluorouracil-substituted nucleic acids and tryptophan-containing proteins can be detected by fluorescence characteristic of the uracil-tryptophan fluorophore. The mechanism proposed for the formation of photoproducts
6 and
7 involves electrophilic attack of the 5-uracilyl cation on the indole ring of 5.