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Working towards the synthesis of 2′- O-[ N-(aminoethyl)carbamoyl]methyl-modified di- and oligonucleotides, we have synthesised a protected 2′- O-[ N-(aminoethyl)carbamoyl]methyl-modified adenosine where the modification is introduced in a convenient one-pot three-step procedure. The corresponding H-phosphonate building block was also synthesised, and from this intermediate, a 2′- O-[ N-(aminoethyl)carbamoyl]methyl-containing dinucleotide could be made. We also performed studies on the chemical and enzymatic stability of this dinucleotide. The dinucleotide was subjected to different ammonolysis and other basic conditions, and HPLC analysis showed that the modification was intact to most conditions, but that there was some minor hydrolysis when NH3 (concd. aq .) was used at 55 °C. Under several other sets of conditions, including saturated NH3 in methanol, and ethylenediamine, the amide remained intact. Treatment of the dinucleotide with Phosphodiesterase I from Crotalus adamanteus venom and Phosphodiesterase II from bovine spleen showed that the N-(aminoethyl)carbamoylmethyl moiety gives the phosphodiester linkage substantial protection against enzymatic degradation; the phosphodiester was not degraded by PDE II at all after seven days. [ABSTRACT FROM AUTHOR]