Abstract
A highly efficient method for the preparation of LNA (Locked Nucleic Acid) phosphoramidite
monomers with 2-cyanoethyl-N,N,N′,N′-tetraisopropylphosphorodiamidite and 4,5-dicyanoimidazole has been devised. The
quality of the phosphoramidites prepared in this manner is equal to HPLC purified
phosphoramidites and can easily be used for oligonucleotide synthesis without further
purification. In addition the possibility of using 4,5-dicyanoimidazole in catalytic
amounts has been investigated and showed optimum results when 0.7 equivalent was used,
and that reducing the amount further leads to undesired phosphitylation of the nucleobase.
Furthermore it is demonstrated that LNA phosphoramidite monomers are exceedingly stable
in acetonitrile solution thereby prolonging the effective lifetime of the reagent
significantly.
Key words
phosphoramidites - phosphitylations - phosphitylation activators - nucleotide analogues
- bicyclic compounds
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