R. Rai, P. S. Pandey / Bioorg. Med. Chem. Lett. 15 (2005) 2923–2925
2925
Table 1. 1H NMR titration data of adenine derivative 2, flavin
derivative 5 and uracil derivative 6
Concn of uracil
6 added (M)
d (N–H)
Adenine 2
d (N–H)
Flavin 5
d (N–H)
Uracil 6
0.000
0.008
0.016
0.024
0.032
0.040
0.048
0.056
0.064
0.072
0.080
0.088
6.190
6.307
6.395
6.458
6.517
6.554
6.581
6.631
6.668
6.697
6.723
6.761
10.390
10.319
10.213
10.119
10.070
10.021
9.984
—
9.825
9.758
9.710
9.690
9.665
9.646
9.660
9.670
9.673
9.685
9.690
9.973
9.967
9.956
9.954
9.936
Figure 1. 1:1 complex of derivatives 2 and 5.
well for 1:1 complex with the binding constant of
2.21 · 103 MÀ1. The proposed structure of the 1:1 com-
plex is given in Figure 2.
ton of the uracil derivative. However, when the
concentration of uracil derivative becomes very high,
there is a trend of increase in the chemical shift (down-
field shift). This is quite understandable, because, as the
concentration of uracil increases, the ratio of the concen-
tration of the uncomplexed uracil to the complexed uracil
also increases, which leads to the upfield shift of the aver-
age –NH proton signal. At the higher concentration of
the uracil, the dimerization of uracil derivative may be
responsible for the downfield shift of the –NH proton.
4. Competitive binding of adenine with flavin and uracil
derivatives
The comparative binding of the steroidal adenine with
flavin and uracil derivatives was also carried out. To
the mixture of flavin (0.005 M) and adenine derivative
(0.01 M) in 2% CH3OH in CDCl3, different concentra-
tions of uracil derivative were added and 1H NMR
1
In summary, we have carried out the comparative bind-
ing studies to establish the competitive binding of ade-
nine towards flavin and uracil, which may be useful in
future, for designing inhibitors based on flavin deriva-
tives for DNA/RNA polymerases.
was recorded after each addition. The H NMR spec-
trum showed the changes in the chemical shift values
of NH of all the three derivatives. It was observed that
initially, addition of uracil showed slight effect on the
chemical shifts of imide N–H of both flavin and uracil.
However, as the addition of uracil was increased, the
changes in the chemical shifts indicated the gradual
replacement of the flavin derivative by uracil derivative.
As the concentration of uracil reaches 0.088 M, the
chemical shift value of imide proton of flavin ap-
proaches nearly the same value of imide proton of un-
bound flavin, thus showing that uracil replaces the
flavin completely from the binding site of adenine (Table
1). This observation clearly indicates that both uracil
and flavin are competing for the same binding site of
the adenine, that is, the Watson–Crick site.
Supplementary data
Supplementary data associated with this article can be
References and notes
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