Nucleic Acids Research, Vol 24, Issue 8 1554-1560, Copyright © 1996 by Oxford University Press
X Zhao, S Nadji, JL Kao and JS Taylor
Irradiation of the dinucleotide TpdA and TA-containing oligonucleotides and
DNA produces the TA* photoproduct which was proposed to be the [2+2]
cyclo-addition adduct between the C5-C6 double bonds of the T and the A
[Bose,S.N., Kumar,S., Davies,R.J.H., Sethi,S.K. and McCloskey,J.A. (1984)
Nucleic Acids Res. 12, 7929-7947]. The proposed structure was based on a
variety of spectroscopic and chemical degradation studies, and the
assignment of a trans-syn-I stereochemistry was based on an extensive
1H-NMR and molecular modeling study of the dinucleotide adduct
[Koning,T.M.G., Davies,R.J.H. and Kaptein,R. (1990) Nucleic Acids Res. 18,
277-284]. However, a number of properties of TA* are not in accord with the
originally proposed structure, and prompted a re-evaluation of the
structure. To assign the 13C spectrum and establish the bond connectivities
of the TA* photoproduct of TpdA [d(TpA)*], 1H-13C heteronuclear
multiple-quantum coherence (HMQC) and heteronuclear multiple bond
correlation (HMBC) spectra were obtained. The 13C shifts and connectivities
were found to be inconsistent with the originally proposed cyclobutane ring
fusion between the thymine and adenine, but could be explained by a
subsequent ring-expansion reaction to give an eight-membered ring valence
isomer. The new structure for the d(TpA)* resolves the inconsistencies with
the originally proposed structure, and could have a stereochemistry that
arises from the anti, anti glycosyl conformation found in B form DNA.
ARTICLES
The structure of d(TpA), the major photoproduct of thymidylyl-(3'5')- deoxyadenosine
Department of Chemistry, Washington University, St Louis, MO 63130, USA.
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