Mixed-backbone oligonucleotides containing segments of deoxynucleosides phosphorothioate and 2 '-O-methylribonucleosides methylphosphonate: Synthesisand properties

Synthesis of mixed-backbone oligonucleotides containing segments of deoxynu cleoside phosphorothioate and 2'-O-methylribonucleoside methylphosphonate h ave been achieved by using N-Pent-4-enoyl (PNT) heterocyclic base-protected 2'-O-methylribonucleoside methylphosphonamidites. Use of PNT for heterocyc lic base-protection allows the deprotection to be carried out under milder conditions without affecting base labile methylphosphonate internucleotide linkages. New MBOs have reduced phosphorothioate internucleotide linkages w hile maintaining affinity with target RNA and are stable towards nucleases.