1. Figure 1. LC-MS/MS for monitoring the formation of N 3-CMdT and O⁴ -CMdT in calf thymus DNA upon treatment with diazoacetate. Shown are the SICs for monitoring the m/z 301→185 transition, corresponding to the loss of a 2-deoxyribose, from the LC-MS/MS analyses with the injection of: (a)N 3-CMdT standard; (b)O⁴ -CMdT standard; (c) enzymatic digestion mixture of calf thymus (ct) DNA treated with 20 mM potassium diazoacetate (KDA, and the LC-MS/MS results from the reaction with 8 mM KDA are shown in Figure S7); (d) the sample in (c) with the addition of standard N 3-CMdT; and (e) the sample in (c) with the addition of standard O⁴ -CMdT.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

2. Figure 2. Tandem mass spectra supporting the formation of N 3-CMdT and O⁴ -CMdT in calf thymus DNA. Shown are the MS ³ results, which monitors the further fragmentation of the protonated carboxymethylthymine ( m/z 185), for: (a) standard N 3-CMdT; (b) standard O⁴ -CMdT; (c) the 27.8 min fraction shown in Figure 1 c; and (d) the 29.2 min fraction shown in Figure 1 c. Depicted in the insets are the corresponding MS/MS for the [M + H] ⁺ ions of the modified nucleosides. The ion of m/z 185 found in MS/MS is attributed the elimination of a 2-deoxyribose.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

3. Scheme 3. The incorporation of N 3-CMdT into ODNs.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

4. Scheme 2. The chemical synthesis of N 3-CMdT and O⁴ -CMdT.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

5. Scheme 1. The formation of diazoacetate and its modification of 2′-deoxyguanosine.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

6. Figure 3. The product-ion spectrum of the ESI-produced [M – 3H] ^3– ions of d(ATGGCGXGCTAT), where ‘X’ represents O⁴ -CMdT. Illustrated in the insets is the negative-ion ESI-MS for the modified ODN.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

7. Scheme 4. The incorporation of O⁴ -CMdT into ODNs.
Chemical synthesis of oligodeoxyribonucleotides containing N 3- and O4 -carboxymethylthymidine and their formation in DNA
Nucleic Acids Res. 2008;37(2): doi: /nar/gkn946
Nucleic Acids Res | © 2008 The Author(s)This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.