Postsynthetic guanidinylation of primary amino groups in the minor and major grooves of oligonucleotides

Two different postsynthetic strategies were employed to introduce guanidinium moieties into oligonucleotides. A 2′-O-(6-aminohexyl) tether, which positions the modification in the minor groove, was selectively deprotected and guanidinylated on the solid support. In the second system, the aminoethoxy spacer of the tricyclic cytosine analog G-clamp, which protrudes into the major groove of the duplex, was guanidinylated in aqueous solution using the fully deprotected oligonucleotide. Both methods were successfully applied to synthesize and characterize various guanidinylated oligonucleotides.