Novel methodology for the preparation and purification of oligonucleotides incorporating phosphorothiolate termini

A novel phosphoramidite; NN-diisopropylamino-2-eyanoethyl-ortho-methylbenzylphosphoramidite 1, was prepared. The reaction of I with DMTrT and subsequent derivatisation of the phosphite triester product under solution-phase, Michaelis-Arbuzov conditions was investigated. Coupling of I with the terminal hydroxyl groups of support-bound oligodeoxyribonucleotides and subsequent reaction with an activated disulfide yielded oligonucleotides bearing a terminal, phosphorothiolate-linked, lipophilic moiety. The oligomers were readily purified using RP-HPLC. Silver(I)-mediated cleavage of the phosphorothiolate linkage and desalting of the oligonucleotides were performed readily in one step to yield cleanly the corresponding phosphate monester-terminated oligomers. (C) 2003 Elsevier Science Ltd. All rights reserved.