Patent ID: 7217805

Claim:
A compound of formula (1) or a pharmaceutically acceptable salt thereof, wherein R 1 selected from the group consisting of a hydrogen atom, a protecting group for a hydroxy group in nucleic acid synthesis, a phosphoric acid group, a phosphoric acid group protected with a protecting group in nucleic acid synthesis, and a group represented by the formula —P(R 4a )R 4b , wherein R 4a and R 4b are the same or different and each represents a hydroxy group, a hydroxy group protected with a protecting group in nucleic acid synthesis, a mercapto group, a mercapto group protected with a protecting group in nucleic acid synthesis, an amino group, an amino group protected with a protecting group in nucleic acid synthesis, an alkoxy group having 1–6 carbon atoms, an alkylthio group having 1–6 carbon atoms, a cyanoalkoxy group having 1–7 carbon atoms, or an amino group substituted by an alkyl group having 1–6 carbon atoms, R 2 represents an azido group, an amino group, or a group represented by the formula —NH—R 3 , wherein R 3 selected from the group consisting of a protecting group for an amino group in nucleic acid synthesis, a phosphoric acid group, a phosphoric acid group protected with a protecting group in nucleic acid synthesis, and a group represented by the formula —P(R 4a )R 4b , wherein R 4a and R 4b are the same or different and each represents a hydroxy group, a hydroxy group protected with a protecting group in nucleic acid synthesis, a mercapto group, a mercapto group protected with a protecting group in nucleic acid synthesis, an amino group, an amino group protected with a protecting group in nucleic acid synthesis, an alkoxy group having 1–6 carbon atoms, an alkylthio group having 1–6 carbon atoms, a cyanoalkoxy group having 1–7 carbon atoms or an amino group substituted by an alkyl group having 1–6 carbon atoms, B represents a purin-9-yl group or a 2-oxo-l,2-dihydropyrimidin-1-yl group each of which is unsubstituted or substituted with 1 or more substituents 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 halogen atom.