Preparation and Physical Properties of Conjugates of Oligodeoxynucleotides with Poly(δ)ornithine Peptides

Oligodeoxynucleotides (12-mers) having either a 3′ aminolinker or both 3′ and 5′ aminolinker groups were synthesized and then reacted with N-iodoacetoxysuccinimide. Separately, a series of peptides, consisting of cysteine carboxyamide and a varying number of residues of ornithine coupled through their side-chain amino groups, was prepared, leaving on the final Fmoc protecting group. Reaction of each Fmoc—peptide with an activated oligodeoxynucleotide yielded the desired conjugates, which were purified by an Fmoc-on/Fmoc-off two-step reversed-phase HPLC procedure. On hybridization with a complementary unmodified 12-mer oligodeoxynucleotide, it was found that there is a gradual increase in melting temperature with the number of ornithine residues, whereas the appended peptide did not perturb the B form of the duplex.