Patent ID: 7994145

Claim:
An oligonucleotide analogue or a pharmaceutically acceptable salt thereof having one or more structural units represented by the following formula (1a): provided that when the oligonucleotide has two or more structural units of formula (1a), each B is the same or different, wherein B represents a purin-9-yl group or a 2-oxo-1,2-dihydropyrimidin-1-yl group which are unsubstituted or substituted with a substituent selected from the group consisting of a hydroxy group, a hydroxy group protected with a protecting group in nucleic acid synthesis, an alkoxy group having 1-6 carbon atoms, a mercapto group, a mercapto group protected with a protecting group in nucleic acid synthesis, an alkylthio group having 1-6 carbon atoms, an amino group, an amino group protected with a protecting group in nucleic acid synthesis, an amino group substituted by an alkyl group having 1-6 carbon atoms, an alkyl group having 1-6 carbon atoms and a halogen atom.