Development of a novel methodology for the synthesis of oligonucleo-peptide conjugates

Sammanfattning: Peptide-oligonucleotide conjugates constitute a new class of antisense molecules that exhibit improved biological activity over standard oligonucleotide analogues. Currently, these oligomeric bioconjugates are prepared by either solution- or solid-phase techniques. The combination of the rather different peptide and oligonucleotide chemistries is somewhat difficult and has led to some limitations of the hybrid sequences and structures that can be synthesized. The present thesis describes the development of new chemical methodologies for synthesis of these hybrid biopolymers by solid-phase techniques. In particular, protecting groups for the alpha-amino group of amino acids and for the side-chain of histidine were evaluated in the context of a new protecting group strategy for the general synthesis of oligonucleotide-peptide conjugates. Acid labile urethanes (Bpoc and Ddz) were evaluated for the temporary protection during peptide elongation. In particular, Bpoc proved to be fully compatible with the very acid-sensitive nucleic acid backbone. A new masking group (the 2,6-Dmbz) for the imidazole function of histidine was developed, which provided synthesis of peptides in good yields and with very limited racemization. This combination of protecting groups was successfully applied to the synthesis of peptideoligonucleotide conjugates of complex structure. This solid-phase approach can also find application in combinatorial techniques for the generation of libraries of peptideoligonucleotide hybrids. A project devoted to identifying peptides that can efficiently bind to single- and doublestranded RNA was initiated. Basic peptides composed of amino acids that are sensitive to pH in the physiological pHrange were shown to stabilize a 2'-0-Me RNA:RNA duplex in a pHdependent fashion. The selected peptides may find application in the form of conjugates with oligonucleotides or as complexing agents for intracellular delivery of antisense molecules.