A simple and efficient method for the preparation of eight phosphoramidite building blocks for incorporation of 2'-O-(2-aminoethoxymethyl)ribonucleosides and 2'-O-(3-aminopropoxymethyl)ribonucleosides into synthetic oligonucleotides has been developed. The synthetic routes are maximally convergent and provide sufficient amounts of phosphoramidites for several solid-phase synthesis coupling reactions. Using acyclic derivatives 17a,b the overall yields of phosphoramidites 2 and 3 were increased up to 50% for pyrimidine nucleosides and up to 30% for purine derivatives with substantial decrease of total reaction steps. The 2'-O-substituent was found to be stable during oligonucleotide synthesis. The resulting oligonucleotides are of particular interest for post-synthetic functionalization and conjugation. (C) 2008 Elsevier Ltd. All rights reserved.