The (α-4) photoconjugates of 5-methylcytosine, 1,5-dimethylcytosine, 1-methylthymine and thymidine.
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.
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA, USA. shetlar@cgl.ucsf.edu
Martin D
MD
Shetlar
Janet
J
Chung
D044503:5-Methylcytosine / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003080:Cold Temperature; D004247:DNA / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D055668:Photochemical Processes; D011740:Pyrimidine Dimers / Q000737:chemistry*; D012996:Solutions; D013936:Thymidine / Q000737:chemistry*; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry; D014466:Ultraviolet Rays; D014867:Water
D011740:Pyrimidine Dimers; D012996:Solutions; D014867:Water; C030630:1-methylthymine; D044503:5-Methylcytosine; D004247:DNA; D013941:Thymine; D013936:Thymidine