Synthesis and hybridizing properties of isoDNAs including 3 '-O,4 '-C-ethyleneoxy-bridged 5-methyluridine derivatives

3',4'-Ethyleneoxy-bridged 5-methyluridine derivatives with methyl groups in the bridge, (R)-Me-3',4'-EoNA-T and (S)-Me-3',4'-EoNA-T, were synthesized, and these two analogs and unsubstituted 3',4'-EoNA-T were successfully incorporated into a 2',5'-linked oligonucleotide (isoDNA). Their duplex-forming ability with complementary DNA and complementary RNA, and triplex-forming ability with double-stranded DNA, were evaluated by UV-melting experiments. The results indicated that isoDNAs, including these 3',4'-EoNA analogs, could hybridize exclusively with complementary RNA. In particular, 3',4'-EoNA-T and (R)-Me-3',4'-EoNA-T modifications within isoDNA could stabilize the duplexes with complementary RNA compared with unmodified or 3',4'-BNA-modified isoDNAs.