The Photoreactions of Thymine with Hypoxanthine and Imidazole

Abstract

<jats:p>Photochemical reactions of thymine linked to hypoxanthine or imidazole by a trimethylene chain were studied in aqueous solution. Irradiation (λ = 254 nm) of thymine-hypoxanthine pair yielded two internal cycloadducts with azetidine and cyclobutane part structures. Sensitization and quenching experiments suggested that the excited singlet was the reactive state in the photo-cycloaddition reactions. Only cyclobutanes were isolated from irradiated (λ = 290 nm) solutions of thymine-imidazole pairs. Photocycloadditions were reversible upon irradiation at λ = 254 nm</jats:p>

The Photoreactivity of Pyrimidine‐purine Sequences in Some Deoxydinucleoside Monophosphates and Alternating Dna Copolymers

“…Accordingly, the structure assigned to the d(Tp1) photoproduct must also be regarded as tentative at this stage. In this connection, there is evidence from the work of Wenska (1985) to exclude photoaddition between thymine and either the C(4)-C(5) or N(7)-C(8) double bonds in hypoxanthine. These modes of photoaddition were observed between the 3-methylthymine and 1-methylhypoxanthine bases in a trimethylene bridged dinucleotide analogue.…”

Structure of 1-[3-(imidazol-1-yl)propyl]thymine

“…The photochemistry of purine-pyrimidine dinucleotides and their analogues in aqueous solution has grown in interest in the last few years (Bose, Davies, Sethi & McCloskey, 1983;Bose, Kumar, Davies, Sethi & McCloskey, 1984;Wenska, Paszyc & Skalski, 1983;Wenska, 1985). However, the available information concerning the possibility of photocycloaddition of purine to pyrimidine and the stability of the resulting photodimers is still limited and ambiguous.…”

“…Irradiation with UV light of an aqueous solution of the title compound leads to a cyclobutane product resulting from cycloaddition of imidazole and thymine C=C double bonds (Wenska, 1985). The product of this photoreaction has a cis-syn configuration (Gdaniec, Wenska & Koziol, 1985).…”