Cis-syn thymine dimers are the major photoproducts of DNA and are the principal cause of mutations induced by sunlight. To better understand the nature of base pairing with cis-syn thymine dimers, we have synthesized a decamer oligodeoxynucleotide (ODN) containing a cis-syn thymine dimer labeled at the N3 of both T's with 15N by two efficient routes from [3- 15N]-thymidine phosphoramidite. In the postsynthetic irradiation route, an ODN containing an adjacent pair of [3-15N]-labeled T's was irradiated and the cis-syn dimer-containing ODN isolated by HPLC. In the mixed building block route, a mixture of cis-syn and trans-syn dimer-containing ODNs was synthesized from a mixture of [3-15N]-labeled thymine dimer phosphoramidites after which the cis-syn dimer-containing ODN was isolated by HPLC. The N3-nitrogen and imino proton signals of an 15N-labeled thymine dimer-containing decamer duplex were assigned by 2D 1H- 15N heterocorrelated HSQC NMR spectroscopy, and the 15N-1H coupling constant was found to be 1.8 Hz greater for the 5′-T than for the 3′-T. The larger coupling constant is indicative of weaker Ç-bonding that is consistent with the more distorted nature of the 5′-base pair found in solution state NMR and crystallographic structures.
|Number of pages||7|
|Journal||Journal of Organic Chemistry|
|State||Published - Feb 17 2006|