Triple, MPEG-conjugated, helix-forming oligonucleotides (TRIPEGXs): Liquid-phase synthesis of natural and chimeric "all-purine" sequences linked to high molecular weight poly(ethylene glycols)

Long "all-purine" oligonucleotides, up to the 20mer, known to be active as antigene effectors, conjugated to high molecular weight monomethoxy poly(et hylene glycol)s (MPEG)s, were successfully synthesized. Through a liquid-ph ase, MPEG-supported process, both natural and chimeric sequences containing selected phosphorothioate backbone modifications were obtained, purified, and characterized. To follow their cellular trafficking, a fluorescent prob e was linked by soluble supported organic reactions to the 5 ' -terminus, a nd the efficiency of the different synthetic procedures for the introductio n of a fluorescein moiety was compared. The usefulness of the fluorescent m arker was estimated by laser confocal microscopy that ascertains that the M PEG-conjugation enhances the oligonucleotide capacity to cross the cellular membranes and to be accumulated inside the nuclei.