Chemistry Letters 2002
223
most stable, and 6D the most unstable monomeric tautomer.7
In order to elucidate the base-pairing properties of these
betainic nucleobases, we performed electrospray ionization mass
1
spectrometry (ESIMS) and H NMR titrations. Spraying 6a,b
ꢁ
from acetonitrile at 0 V fragmentor voltage and 140 C desolvat-
ing gas temperature, the monomeric cationic systems 5a,b as well
þ
as semiprotonated dimers 6a,b ꢂ 6a,b þ H and sodium adducts
þ
8
6
a,b ¼ 6a,b þ Na were detectable. In accordance to the self-
complementary structures (Scheme 3), which resembles dimeric
9
7
10 1
uracilyl-betaines and m g derivatives, H NMR signals shifted
typically upfield on dilution.11
Scheme 4.
þ
of the monomeric 7 þ Na , of 1 : 1 associates such as 7 ꢂ
þ
þ
6
a,b þ H (Scheme 4), and of 72 þ Na in ESIMS.
The Deutsche Forschungsgemeinschaft (DFG) and the Fonds
der Chemischen Industrie (FCI) is gratefully acknowledged for
financial support.
Scheme 3.
Equimolar solutions of 5a,b and 6a,b, respectively, and their
complementary nucleobases cytosine and cytidine, respectively,
sprayed from acetonitrile solutions gave additional peaks which
References and Notes
1
P. A. Limbach, P. F. Crain, and J. A. McCloskey, Nucleic Acid
Res., 22, 2183 (1994).
8
correspond to 1 : 1 base-pairs. No associates were detected with
guanine under analogous conditions. NMR titrations in DMSO-d6
at rt were performed at total nucleobase concentration, and the
mole fraction of cytidine was increased from 0 to 0.99. The
chemical shifts of the N(1)H and NH2 group of e.g. 5a (Scheme 4)
shifted steadily downfield with increasing concentration of
cytidine, thus indicating horizontal interactions. As expected
for a Watson-Crick-type base-pairing, Áꢁ[N(1)-H] was essen-
tially twice as large as Áꢁ[NH2].
2
C. G. Edmons, P. F. Crain, R. Gupta, T. Hashizume, C. H.
Hocart, J. A. Kowalak, S. C. Pomerantz, K. O. Stetter, and J. A.
McCloskey, J. Bacteriol., 173, 3138 (1991); C. W. Gehrke and
K. C. Kuo, J. Chromatogr., 417, 3 (1989); V. S. Zueva, A. S.
Mankin, A. A. Bogdanov, D. L. Thurlow, and R. A.
Zimmermann, FEBS Lett., 188, 233 (1985); Y. Kuchino, M.
Ihara, Y. Yabusaki, and S. Nishimura, Nature, 298, 684 (1982).
R. Liou and T. Blumenthal, Mol. Cell Biol., 10, 1764 (1990); G.
Dirheimer, in ‘‘Modified Nucleosides and Cancer,’’ ed. by G.
Glass, Springer-Verlag, Heidelberg (1983), pp 15–46.
W. D. Ollis, S. P. Stanforth, and C. A. Ramsden, Tetrahedron,
3
4
5
4
1, 2239 (1985).
A. Schmidt, M. K. Kindermann, and M. Nieger, Heterocycles,
1, 237 (1999); A. Schmidt and M. K. Kindermann, J. Org.
5
Chem., 62, 3910 (1997).
J. C. Parham, T. G. Winn, and G. B. Brown, J. Org. Chem., 36,
6
2
639 (1971).
7
8
6A: ÁHf (PM3) ¼ 249:20 KJ/mol; 6D: ÁHf ¼ 356:75 KJ/mol.
e.g. 6b: m/z ¼ 272:1, 543.2, 565.2 amu; e.g. 6b þ cytosine:
m/z ¼ 383:2, 405.1 amu.
1
9
1
A. Schmidt, M. K. Kindermann, P. Vainiotalo, and M. Nieger, J.
Org. Chem., 64, 9499 (1999).
Figure 1. Variations in H NMR chemical shifts in
N(1)H and NH2 of 5a on addition of cytidine.
0 T. Ishida, M. Katsuta, M. Inoue, Y. Yamagata, and K. Tomita,
Biochem. Biophys. Res. Commun., 115, 849 (1983); S. Metzger
and B. Lippert, Angew. Chem., Int. Ed. Engl., 35, 1228 (1996).
Spraying acetonitrile solutions of the self-complementary
phosphoric acid 5-[2-amino-6(1H)-oxopurin-9-yl]-3-[2-chloro-
phenoxy(2-cyanoethoxy)phosphinoyloxy]tetrahydrofuran-2-yl-
methyl 5-[4-amino-2(1H)-oxopyrimidin-1-yl]-2-[phenybis(4-
methoxyphenyl)methoxymethyl]tetrahydrofuran-3-yl 2-chloro-
phenyl phosphate d(CpGp) 7 and the betaines 6a,b gave peaks
11 e.g. for 6b in DMSO-d6 at rt from 20 mM to 6 mM: Áꢁ ¼
À0:15 ppm (NH), À0:22 ppm (NH2Þ, À0:03 ppm (ꢂ-H).
12 e.g. for 6b: m/z ¼ 1410:2, 1659.2, 2797.4 amu.