completely stable to conditions for phosphoramidite and
oligonucleotide synthesis. Fine-tuning of duplex stability,
crosslink selectivity and yield is thus possible depending on
the specific choice of the building block and desired target.
From current and previous studies on furan modification, it
appears plausible to use a 20-amido-linker for pyrimidine
nucleoside and a 20-O-alkyl-linker for purine nucleoside
modification. As such, in view of its synthetic accessibility,
its complementarity with the earlier developed furan-modified
uridine, its more beneficial influence on duplex stability and its
observed crosslink selectivity, the here described 20-O-furanyl-
propyladenosine is a valuable addition to our recently developed
toolbox for furan-oxidation induced crosslinking.
Fig. 3 ICL-formation of 8, analyzed by 20% denaturing PAGE,
with A* opposite to A, C, T and G in a duplex DNA (lanes 5–8). Far
right: structure of reactive ketoenal formed upon oxidation of a furan
moiety.
structures.17,21 Considering duplex stability, internal incorpo-
ration of the 20-O-(3-propyl)-furan modified nucleoside leads
to more stable duplexes than internal incorporation of the
furan-modified 20-amido-uridine in similar sequences (DTm varying
between ꢂ3.6 and ꢂ19.9 1C).22 The most stable duplexes are
formed when A* is incorporated in between two guanosines
(11) and placed opposite to A or C. This increase in stability
does not affect A or C crosslinking selectivity, therefore
excluding the possibility of correlation between duplex stability
and selectivity in ICL formation.
Notes and references
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In conclusion, we have developed a straightforward synthesis
of a 20-O-furanylpropyl adenosine building block. Incorpora-
tion into double-stranded DNA reduced duplex stability loss
in comparison with the previously reported 20-amido-uridine
and acyclic furan-modified building blocks. Incorporation
within a G(A*)G/CCC context even leads to a >5 1C stabili-
sation of the 12-mer duplex. The current investigation further
identified NIS as a superior oxidant over NBS in terms of
stoichiometry for the crosslinking reaction.
The selectivity of this new furan-modified purine derivative
in furan-oxidation crosslinking was evaluated to show preferential
reaction with A and C (with a surprising slight preference for
crosslinking to A). Though in this specific case, yields are
not the highest, a combination of features renders the furan-
oxidation crosslink methodology very attractive. Benefitting
from an induced reactivity principle and proximity being a
prerequisite for crosslinking, we have demonstrated that only
equimolar amounts of modified strands are necessary to
produce substantial amounts of crosslinked material without
collateral damage or undesired side reactions. Formation of
stable crosslinked duplexes is fast and purification is facile in
view of the ‘self-destructing’ behaviour of the furan-modified
strands. As illustrated by current and previous work,16,17,22
construction of the furan modified nucleoside building blocks
benefits from the commercial availability of a broad range of
furan derivatives and follows a very modular and straight-
forward synthetic route. There is no need for orthogonal
protective group manipulations as the furan moiety is
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2798 Chem. Commun., 2011, 47, 2796–2798
This journal is The Royal Society of Chemistry 2011