Solid-phase synthesis of terminal oligonucleotide-phosphoramidate conjugates

A novel phosphoramidite, N,N-diisopropylamino-2-cyanoethyl-9-anthacenemethyl 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 I 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 I under the same conditions. Oligonucleotides modified with a terminal phosphate monoester, lipophilic, fluorescent or cationic groups were thus prepared. (c) 2005 Elsevier Ltd. All rights reserved.