title: The photochemistry of thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine in aqueous solution.
abstract: The photochemistry of the dinucleoside monophosphate thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine (Tpm5dC) has been studied in aqueous solution using both 254 nm and UV-B radiation. A variety of dinucleotide photoproducts containing 5-methylcytosine (m5C) have been isolated and characterized. These include two cyclobutane dimers (CBD) (the cis-syn [c,s]and trans-syn forms), a (6-4) adduct and its related Dewar isomer, and two isomers of a product in which the m5C moiety was converted into an acrylamidine. Small amounts of thymidylyl-(3'-5')-thymidine (TpT) were also formed, presumably as a secondary photoreaction product. In addition, a photoproduct was characterized in which the m5C moiety was lost, thus generating 3'-thymidylic acid esterified with 2'-deoxyribose at the 5-hydroxyl on the sugar moiety. The c,s CBD of Tpm5dC readily undergoes deamination to form the corresponding CBD of TpT. The kinetics of this deamination process has been studied; the corresponding enthalpy and entropy of activation for the reaction have been evaluated at pH 7.4 as being, respectively, 73.4 kJ/mol and -103.5 J/K mol. Deamination was not observed for the other characterized photoproducts of Tpm5dC.
authors.affiliation: Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA 94143-0446, USA.
authors.forename: Lech
authors.initials: L
authors.lastname: Celewicz
authors.forename: Moriz
authors.initials: M
authors.lastname: Mayer
authors.forename: Martin D
authors.initials: MD
authors.lastname: Shetlar
mesh_terms: D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D007700:Kinetics; D008968:Molecular Conformation; D010777:Photochemistry; D012996:Solutions / Q000737:chemistry; D013936:Thymidine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000528:radiation effects; D013997:Time Factors; D014466:Ultraviolet Rays; D014867:Water / Q000737:chemistry
chemical_list: D012996:Solutions; C089794:thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine; D014867:Water; D003841:Deoxycytidine; D013936:Thymidine