Biomedical Engineering Reference
In-Depth Information
Scheme 3.6
-Se-phosphate modifi-
cation. (
a
) 2-Chloro-4H-[1, 3, 2]-benzodioxaphosphorin-4-one (salicyl phosphorochloridite) and
pyrophosphate. (
b
) Benzo-1,2-thiaselenol-3-one (BTSE) and Et
3
N, dioxane. (
c
) Diluted NH
3
Synthesis of deoxy- and ribonucleoside triphosphates with
'
DNA and PSe-RNA synthesis. The conditions of the enzymatic reactions are
mild, and the synthesized PSe-nucleic acids are diastereoisomerically pure, which
allows us to make longer oligonucleotides with the PSe groups incorporated at
various sites. We have developed the synthesis (Scheme
3.6
)ofSe-dNTPsandSe-
NTPs (
-phosphoroselenoate triphosphates) [
28
] and the Se-nucleobase-modified
triphosphates [
58
]. Moreover, we have found that they can be generally recognized
by DNA as well as RNA polymerases [
88
-
90
]. More interestingly, after the
modification of a catalytic RNA (hammerhead ribozymes) by PSe, it can retain its
activity up to the native level.
'
3.4
Nucleobase Modifications of Nucleic Acids
with Chalcogens
Simple replacement of the oxygen atoms on nucleobases with other chalcogen
elements (such as S and Se) can lead to numerous interesting properties. For
example, 2-thiothymidine could be applied to a synthetic biology system to
improve replication accuracy. Benner's lab has reported that the fidelity of PCR
reaction involving artificial base pairs (isoC/isoG) could be significantly improved,
simply by replacing TTP with 2-thioTTP in PCR reaction, since 2-thioT can
discriminate against isoG [
79
]. Enhanced base pairing and replication efficiency
of thiothymidines were also reported by Kool's lab [
59
]. The large chalcogen atoms
on nucleobases could be used to electronically and sterically alter the fidelity of
the base pairing. This interesting characteristic may prove useful in nucleic acid
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