Herein, we report a straightforward one-step procedure
for modifying
N
-nucleophilic groups in the nucleobases
of commercially
available nucleoside phosphoramidites. This method involves the deprotonation
of amide groups under phase-transfer conditions and subsequent reaction
with electrophilic molecules such as alkyl halides or organic isocyanates.
Using this approach, we obtained 10 different classes of modified
nucleoside phosphoramidites suitable for the synthesis of oligonucleotides,
including several noncanonical nucleotides found in natural RNA or
DNA (e.g., m
6
A, i
6
A, m
1
A, g
6
A, m
3
C, m
4
C, m
3
U, m
1
G,
and m
2
G). Such modification of nucleobases is a common
mechanism for post-transcriptional regulation of RNA stability and
translational activity in various organisms. To better understand
this process, relevant cellular recognition partners (e.g., proteins)
must be identified and characterized. However, this step has been
impeded by limited access to molecular tools containing such modified
nucleotides.