Characterization of thymidine ultraviolet photoproducts. Cyclobutane dimers and 5,6-dihydrothymidines

We describe the preparation of the six configurationally distinct cyclobutane-type photodimers generated by the acetone-sensitized uv irradiation of thymidine in aqueous solution. Also prepared as minor photoproducts are the 5R and 5S di-astereoisomers of 5,6-dihydrothymidine, and two novel molecules, the 5R and 5S diastereoisomers of 5-acetonyl-5,6-dihydrothymidine. The purification of the ten molecules by chromatographic techniques (hplc, tlc) is described, along with their extensive characterization by uv, ir, cd, FAB-ms and 1H nmr. The proton chemical shifts and coupling constants are discussed in terms of the geometry of the pyrimidine, cyclobutane, and sugar rings.