The photoinduced cycloreversion of oxetanes has been thoroughly investigated in connection with the photorepair of the well-known DNA (6-4) photoproducts. In the present work, the direct photolysis of the two...

Benzophenone (BP) is present in a variety of bioactive molecules. This chromophore is able to photosensitize DNA damage, where one of the most relevant BP/DNA interactions occurs with thymine (Thy). In view of the complex photoreactivity previously observed for dyads containing BP covalently linked to thymidine, the aim of this work is to investigate whether appropriate changes in the nature of the spacer could modulate the intramolecular BP/Thy photoreactivity, resulting in an enhanced selectivity. Accordingly, the photobehavior of a series of dyads derived from BP and Thy, separated by linear linkers of different length, has been investigated by steady-state photolysis, as well as femtosecond and nanosecond transient absorption spectroscopy. Irradiation of the dyads led to photoproducts arising from formal hydrogen abstraction or Paternò-Büchi (PB) photoreaction, with a chemoselectivity that was clearly dependent on the nature of the linking bridge; moreover, the PB process occurred with complete regio-and stereoselectivity. The overall photoreactivity increased with the length of the spacer and correlated well with the rate constants estimated from the BP triplet lifetimes. A reaction mechanism explaining these results is proposed, where key features are the strain associated with the reactive conformations and the participation of triplet exciplexes. ASSOCIATED CONTENTSupporting Information. 1 H and 13 C NMR spectra of the synthesized dyads and intermediates. UV, femtosecond transient absorption and laser flash photolysis spectra and kinetics. X-Ray crystallography data for Ox-D10.

Direct absorption of UVB light by DNA may induce formation of cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6-4) photoproducts. The latter arise from the rearrangement of unstable oxetane intermediates, which have...