A 2-5A analog represented by the formula (1): <；CHEM>； Äwherein m is 0 or 1； n is 0 to 2； R<；1>； represents an alkoxy group having from 1 to 6 carbon atoms which may have a substituent, a mercapto group, a mercapto group protected by a nucleic acid synthesis protecting group, or an alkylthio group having from 1 to 4 carbon atoms which may have a substituent； R<；2>；, R<；3>；, R<；4>；, R<；5>； and R<；6>； represent a hydroxyl group, a hydroxyl group protected by a nucleic acid synthesis protecting group, an alkoxy group having from 1 to 6 carbon atoms which may have a substituent, a mercapto group, a mercapto group protected by a nucleic acid synthesis protecting group, or an alkylthio group having from 1 to 4 carbon atoms which may have a substituent； R<；7>； represents an oxygen atom, or a -O(CH2CH2O)q- group (q is 2 to 6)； R<；8>； represents a hydrogen atom, an alkyl group having from 1 to 6 carbon atoms which may have a substituent, or 5'-phosphorylated oligonucleotide analogs which do not have one hydroxyl group on a 5'-phosphoric acid group； E<；1>；, E<；2>；, E<；3>； and E<；4>； represent a naturally occurring or modified nucleic acid unitÜ, and a pharmacologically acceptable salt thereof.
