1706
M. Sekine et al. / Tetrahedron Letters 44 (2003) 1703–1707
1-hydroxy-4-nitro-benzotriazole gave lower yields of
the product.
Application of this method to the synthesis of
A5%ppd(CpTpTpApCpCpT) (21) was carried out by use
of 6-N,2%,3%-O-tribenzoyladenosine 5%-phosphorimida-
zolidate (22) which was similarly synthesized from the
corresponding 5%-phosphonate derivative (23) and acti-
vated by addition of 6-(trifluoromethyl)-1-hydroxy-4-
nitrobenzotriazole, as shown in Scheme 4. Thus, the
desired 5%-adenylated product 21 was isolated in 16%
yield. Since, usually, the isolated yields of unmodified
oligodeoxynucleotides are ca. 30%, this isolated yield is
reasonable in consideration of the efficiency of ca. 65%
in the pyrophosphate bond formation.
Figure 6. Anion exchange HPLC profile of the crude 24
obtained by ligation of a mixture of 26 with 25 or 21. Panel
A: without 5%-adenylation; 50 mM Tris–HCl (pH 8), 10 mM
MgCl2, 10 mM DTT, 10 mM ATP. Panel B: with 5%-adenyla-
tion; 50 mM Tris–HCl (pH 8), 10 mM MgCl2, 10 mM DTT.
Finally, we used this 5%-adenylated oligodeoxynucle-
otide derivative to obtain m23,2,7G5%pppAmpUmpApd-
(CpTpTpApCpCpT) (24). To demonstrate the
efficiency of the adenylation on ligase reaction, we
studied both reactions of A5%ppd(CpTpTpApCpCpT)
(21)
and
pd(CpTpTpApCpCpT)
(25)
with
m32,2,7G5%pppAmpUmpA (26)6 in the presence of RNA
ligase under the conditions described in Figure 6. It was
clearly shown that the adenylated species gave better
results than the unmodified oligodeoxynucleotide. After
48 h, the product was formed in 58% yield (HPLC)
while the product was formed in only 10% in the case
of the unmodified oligodeoxynucleotide. Separation of
the desired product by HPLC followed by workup gave
m23,2,7G5%pppAmpUmpApdd(CpTpTpApCpCpT) (24) in
an isolated yield of 19%.
In conclusion, we were able to synthesize the TMG-
capped RNA–DNA chimeric molecule. It should be
noted that the 5%-adenylation on the polymer support
should be improved. Now work is under way in this
direction.
Acknowledgements
This work was supported by a Grant-in-Aid (14208074)
for Scientific Research from the Ministry of Education,
Science, Sports, and Culture, Japan.
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