title: The (5-4) and (6-4) adducts of 1-methylthymine and their Dewar valence isomers.
abstract: Previous studies of the photochemical reaction of 1-methylthymine (MeT) in frozen aqueous solution have indicated that four cyclobutane type dimers are formed. We have restudied this system and have found that, in addition to cyclobutane dimers, both a (5-4) adduct and a (6-4) adduct of MeT are formed in significant amounts. Upon standing in aqueous solution, the (5-4) adduct is susceptible to reaction to form an isomeric form of the parent adduct, possibly via ring-opening and closure reactions at C-6 of the saturated pyrimidine ring component of the adduct. Irradiation of each of these three adducts with UVB light produces a pair of Dewar-type adducts. The nine products were individually characterized by mass spectrometry, proton NMR spectroscopy and UV spectroscopy. A less comprehensive study showed that irradiation of thymidine in frozen aqueous solution produces a diastereomeric pair of (5-4) adducts, along with the previously known diastereomeric pair of (6-4) adducts.
authors.affiliation: Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA, USA. shetlar@cgl.ucsf.edu
authors.forename: Martin D
authors.initials: MD
authors.lastname: Shetlar
authors.forename: Janet
authors.initials: J
authors.lastname: Chung
mesh_terms: D002851:Chromatography, High Pressure Liquid; D003080:Cold Temperature; D003500:Cyclization / Q000528:radiation effects; D019281:Dimerization; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D010777:Photochemistry / Q000379:methods*; D011743:Pyrimidines / Q000737:chemistry*; D012996:Solutions; D013941:Thymine / Q000031:analogs & derivatives* / Q000737:chemistry; D014466:Ultraviolet Rays; D014867:Water
chemical_list: D011743:Pyrimidines; D012996:Solutions; D014867:Water; C030630:1-methylthymine; D013941:Thymine