Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA, USA.
Photochem Photobiol. 2012 Mar-Apr;88(2):336-43. doi: 10.1111/j.1751-1097.2011.01070.x. Epub 2012 Jan 23.
The pyrimidine nucleobases contained in DNA undergo a variety of photoinduced reactions in which two moieties become joined to form a product (e.g. formation of cyclobutane dimers and [6-4] adducts). Herein, we describe a new type of photoconjugation reaction that has been shown to occur for 5-methylcytosine (5-MeC), 1,5-dimethylcytosine (1,5-diMeC), 1-methylthymine and thymidine; in this reaction the 5-methyl group of one nucleobase (or nucleoside) becomes attached to the 4-position of the second moiety. For example, 5-MeC forms α-4'-(5'-methylpyrimidin-2'-one)-5-methylcytosine. The various (α-4) conjugates are produced upon irradiation of the parent compound in frozen aqueous solution at -78.5°C. The UV spectra of these compounds display a characteristic "double humped" profile, similar to that expected from overlaying the spectrum of parent nucleobase with that of a 2'-pyrimidone moiety. Preliminary results suggest that thymine and 5-methyl-2'-deoxycytidine (5-MedCyd) form analogous photoproducts. A variety of other previously unreported photoproducts are described as well for the 5-MeC, 1,5-diMeC and 5-MedCyd systems.
DNA 中的嘧啶核苷碱基会经历多种光诱导反应，其中两个部分结合形成产物（例如，形成环丁烷二聚体和[6-4]加合物）。在此，我们描述了一种新的光偶联反应类型，已经证明 5-甲基胞嘧啶 (5-MeC)、1,5-二甲基胞嘧啶 (1,5-diMeC)、1-甲基胸腺嘧啶和胸苷都能发生这种反应；在该反应中，一个碱基（或核苷）的 5-甲基基团连接到第二个部分的 4-位。例如，5-MeC 形成 α-4'-(5'-甲基嘧啶-2'-酮）-5-甲基胞嘧啶。在 -78.5°C 的冷冻水溶液中辐照母体化合物时，会生成各种（α-4）缀合物。这些化合物的 UV 光谱显示出特征的“双峰”轮廓，类似于将母体碱基的光谱与 2'-嘧啶酮部分的光谱叠加的预期。初步结果表明，胸腺嘧啶和 5-甲基-2'-脱氧胞苷 (5-MedCyd) 形成类似的光产物。还描述了其他各种以前未报道过的 5-MeC、1,5-diMeC 和 5-MedCyd 体系的光产物。
