Scaleable and efficient synthesis of 2'-deoxy-2'-N-phthaloyl nucleoside phosphoramidites for oligonucleotide synthesis.

2'-Deoxy-2'-N-phthaloyl nucleosides were prepared from arabino nucleosides by triflate displacement with phthalimide in the presence of DBU. The corresponding phosphoramidites suitable for automated oligonucleotide synthesis were also synthesized. The scalability of described procedures was demonstrated on a 100-g scale preparation of 2'-deoxy-2'-amino-C phosphoramidite.