Solid-phase synthesis of terminal oligonucleotide–phosphoramidate conjugates

Abstract

A novel phosphoramidite, N, N-diisopropylamino-2-cyanoethyl-9-anthracenemethyl phosphoramidite 1 , was prepared and coupled with the terminal 5′-hydroxyl of support-bound T 10 and the putative phosphite triester intermediate was subsequently reacted with iodine in the presence of either water or a series of primary and secondary amines. The reactivity of 1 compared to a previously reported benzyl phosphoramidite 2 was also investigated: oxidation of the product of coupling 2 with CPG-T 10-5′OH under aqueous conditions resulted in greater than 30% of the benzyl moiety being retained. In contrast, essentially complete loss of the 9-anthracenemethyl group was observed using 1 under the same conditions. Oligonucleotides modified with a terminal phosphate monoester, lipophilic, fluorescent or cationic groups were thus prepared.