phosphoramidite and thymidine-glycol

Thymidine glycol (Tg), which is also known as 5,6-dihydroxy-5,6-dihydrothymidine, and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) are two major types of DNA damage products induced by reactive oxygen species (ROS). Here, we report the synthesis of oligodeoxyribonucleotides (ODNs) containing both Tg and 8-oxodG. The dual incorporation of the two single-base lesions was achieved by using a phosphoramidite building block of 8-oxodG with ultramild base protecting group and a building block of Tg whose nucleobase hydroxyl groups were protected with acetyl functionality. The availability of ODNs carrying neighboring 8-oxodG and Tg provided authentic substrates for assessing the formation and examining the replication and repair of this kind of tandem lesions. In addition, thermodynamic parameters derived from melting temperature data revealed that tandem lesions destabilized the double helix to a greater extent than either of the two single-base lesions alone. The thermodynamic results could offer a basis for understanding the repair of the tandem base lesions.

Topics: 8-Hydroxy-2'-Deoxyguanosine; Deoxyguanosine; Gas Chromatography-Mass Spectrometry; Molecular Structure; Oligodeoxyribonucleotides; Organophosphorus Compounds; Spectrometry, Mass, Electrospray Ionization; Thermodynamics; Thymidine

Hydroxyl radical can be induced from Fenton reaction or gamma radiolysis of water. It can add preferentially to the C5 position of thymidine to give the 5-hydroxy-5,6-dihydrothymidin-6-yl radical. In this report, we examined the independent generation and reactivity of this radical in oligodeoxyribonucleotides (ODNs). Our results showed that the major products originated from this radical in single- and double-stranded ODNs were thymidine glycol, 5-hydroxy-5,6-dihydrothymidine, thymidine, and abasic site lesion. A cross-linking lesion, where the C6 of 5-hydroxy-5,6-dihydrothymidine and the C8 of its neighboring guanine are covalently bonded, could be induced from the independently generated radical in dinucleoside monophosphate and trinucleoside diphosphates. The formation of this type of cross-link product in duplex ODNs from either the independently generated radical or gamma irradiation was near or below the detection limit of the LC-MS/MS method that we used.

Topics: Free Radicals; Gamma Rays; Hydroxyl Radical; Molecular Structure; Oligodeoxyribonucleotides; Organophosphorus Compounds; Single-Strand Specific DNA and RNA Endonucleases; Stereoisomerism; Thymidine; Ultraviolet Rays