Oligonucleotides with 2 '-O-carboxymethyl group: synthesis and 2 '-conjugation via amide bond formation on solid phase

An efficient method for synthesis of oligonucleotide 2'-conjugates via amide bond formation on solid phase is described. Protected oligonucleotides containing a 2'-O-carboxymethyl group were obtained by use of a novel uridine 3'-phosphoramidite, where the carboxylic acid moiety was introduced as its allyl ester. This protecting group is stable to the conditions used in solid-phase oligonucleotide assembly, but easily removed by Pd(0) and morpholine treatment. 2'-O-Carboxymethylated oligonucleotides were then efficiently conjugated on a solid support under normal peptide coupling conditions to various amines or to the N-termini of small peptides to give products of high purity in good yield. The method is well suited in principle for the preparation of peptide - oligonucleotide conjugates containing an amide linkage between the 2'-position of an oligonucleotide and the N-terminus of a peptide.