Model Studies of the (6−4) Photoproduct DNA Photolyase:  Synthesis and Photosensitized Splitting of a Thymine−5,6-Oxetane J. Am. Chem. Soc. 1995, 117, 11375−11376

Abstract

Recent X-ray crystallographic and 1 H-NOE data indicate that the stereochemistry of 1 and 2 was incorrectly assigned. Both 1 and 2 as synthesized are in fact R-rather than -anomers. Compound 3 is correct as shown. The original assignments were made based on correlation with a published proton NMR spectrum of a related phenyl nucleoside, and also by correlation of H-1′ coupling constants to known R-and -nucleosides. It is now evident that these coupling patterns are generally reversed for aromatic C-deoxynucleosides as compared to N-nucleosides. A complete description of this unexpected finding will be published separately. Recent studies of properties of the authentic -anomers in DNA show little change in the results. The data in the manuscript are correct, and the primary conclusions of the paper, involving hydrophobic and hydrophilic interactions in DNA, still stand.

Photolytic splitting of homodimeric quinone-derived oxetanes studied by ultrafast transient absorption spectroscopy and quantum chemistry

“…A comparison of the current theoretical findings from BQ-Ox and NQ-Ox with those previously observed for head-to-head and heat-to-tail oxetane regioisomers composed of benzophenone and dimethylthymine (HH and HT, respectively) 21 shows that the state crossing (CP) occurs prior to the TS region and after the 3 BQ-Ox* diradical in BQ-Ox, NQ-Ox and HT, whereas it is located at the TS region for HH. This imposes an energetic barrier to reach the 3 EXC* structure in BQ-Ox, NQ-Ox and HT, which is not present in HH.…”

“…[13][14][15][16][17] In this regard, since the primary Thyh<iThy dimers are not isolable due to their chemical instability, 18 a variety of model oxetane conjugates composed of benzophenone (BP) and thymine (Thy) or uracil (Ura) derivatives have been employed in order to investigate the mechanism of photoinduced ring opening by means of spectroscopic techniques. [19][20][21][22][23] Although these models are far from the real Thyh<iThy dimers, the BP moiety has been found to be convenient to follow the course of the photoreaction by transient absorption spectroscopy, which allows rapid and quantitative detection of the BP triplet excited state ( 3 BP*), 24 amongst other transient species. Interestingly, irradiation of BP-Thy and/or BP-Ura oxetanes results in some cases in a rare ''adiabatic'' ring splitting process involving diradical species and triplet exciplexes, which ultimately evolve leading to the formation of 3 BP* and Thy (or Ura) in its ground state.…”

Mechanisms and energetics of benzophenone photosensitized thymine damage and repair from Paternò–Büchi cycloaddition

“…24,25 Ulteriorly, without the help of additional photosensitizers or enzymes, the direct photolysis of oxetane adducts formed by the BZP-photosensitized DNA damage and 6-4PPs damage is an effective and feasible approach. 14,26,27 The nanosecond timeresolved absorption studies observed that the photoinduced cycloreversion of oxetane adducts generated the triplet excited BZP along with ground state thymine. 28 The ultrafast timeresolved spectra indicated that the cycloreversion reaction occurred in a stepwise manner in a singlet excited state, and then ISC occurs to produce the triplet carbonyl product.…”