Published online 11 October 2005
Article |
Chemical synthesis and thermodynamic characterization of oxanine-containing oligodeoxynucleotides
1International Innovation Center, Kyoto University Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan 2CREST, JST (Japanese Science and Technology), Kyoto University Gokasho, Uji 611-0011, Japan 3Institute of Advanced Energy, Kyoto University Gokasho, Uji 611-0011, Japan
*To whom correspondence should be addressed. Tel: +81 774 38 3517; Fax: +81 774 38 3524; Email: kmak{at}iae.kyoto-u.ac.jp
Received August 11, 2005. Revised September 8, 2005. Accepted September 8, 2005.
Oxanine (Oxa, O), one of the major damaged bases from guanine generated by NO- or HNO2-induced nitrosative deamination, has been considered as a mutagen-potent lesion. For exploring more detailed properties of Oxa, large-scale preparation of Oxa-containing oligodeoxynucleotide (Oxa-ODN) with the desired base sequence is a prerequisite. In the present study, we have developed a chemical synthesis procedure of Oxa-ODNs and characterized thermodynamic properties of Oxa in DNA strands. First, 2'-deoxynucleoside of Oxa (dOxo) obtained from 2'-deoxyguanosine by HNO2-nitrosation was subjected to 5'-O-selective tritylation to give 5'-O-(4,4'-dimethoxytrityl)-dOxo (DMT-dOxo) with a maximum yield of 70%. Subsequently, DMT-dOxo was treated with conventional phosphoramidation, which resulted in DMT-dOxo-amidite monomer with a maximum yield of 72.5%. The amidite obtained was used for synthesizing Oxa-ODNs: the coupling yields for Oxa incorporation were over 93%. The prepared Oxa-ODNs were employed for analyzing the thermodynamic properties of DNA duplexes containing base-matches of O:N [N; C (cytosine), T (thymine), G (guanine) or A (adenine)]. Melting temperatures (Tm) and thermodynamic stability (
) were found to be lower by 6.83
13.41°C and 2.643
6.047 kcal mol1, respectively, compared with those of oligodeoxynucleotides, which had the same base sequence except that O:N was replaced by G:C (wild type). It has also been found that Oxa-pairing with cytosine shows relatively high stability in DNA duplex compared with other base combinations. The orders of
were O:C > O:T > O:A > O:G. The chemical synthesis procedure and thermodynamic characteristics of Oxa-ODNs established here will be helpful for elucidating the biological significance of Oxa in relation to genotoxic and repair mechanisms.
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