A bridged nucleic acid, 2',4'-BNA COC: synthesis of fully modified oligonucleotides bearing thymine, 5-methylcytosine, adenine and guanine 2',4'-BNA COC monomers and RNA-selective nucleic-acid recognition.

Abstract

Recently, we synthesized pyrimidine derivatives of the 2′-O,4′-C-methylenoxymethylene-bridged nucleic-acid (2′,4′-BNACOC) monomer, the sugar conformation of which is restricted in N-type conformation by a seven-membered bridged structure. Oligonucleotides (BNACOC) containing this monomer show high affinity with complementary single-stranded RNA and significant resistance to nuclease degradation. Here, BNACOC consisting of 2′,4′-BNACOC monomers bearing all four bases, namely thymine, 5-methylcytosine, adenine and guanine was efficiently synthesized and properties of duplexes containing the 2′,4′-BNACOC monomers were investigated by UV melting experiments and circular dichroism (CD) spectroscopy. The UV melting curve analyses showed that the BNACOC/BNACOC duplex possessed excellent thermal stability and that the BNACOC increased thermal stability with a complementary RNA strand. On the other hand, BNACOC/DNA heteroduplexes showed almost the same thermal stability as RNA/DNA heteroduplexes. Furthermore, mismatched sequence studies showed that BNACOC generally improved the sequence selectivity with Watson–Crick base-pairing compared to the corresponding natural DNA and RNA. A CD spectroscopic analysis indicated that the BNACOC formed duplexes with complementary DNA and RNA in a manner similar to natural RNA.