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We designed and synthesized an artificial nucleic acid, [3-(1,2-dihydro-2-oxobenzo[ b ][1,8]naphthyridine)]-2'-deoxy-D-ribofuranose (OBN), with a tricyclic structure in a nucleobase as a thymidine analog. Oligodeoxynucleotides (ODNs) containing consecutive OBN displayed improved duplex-forming ability with complementary single-stranded (ss) RNA and triplex-forming ability with double-stranded DNA in comparison with ODNs composed of natural thymidine. OBN-modified ODNs also displayed enhanced enzymatic resistance compared with ODNs with natural thymidine and phosphorothioate modification, respectively, due to the structural steric hindrance of the nucleobase. The fluorescence spectra of OBN-modified ODNs showed sufficient fluorescence intensity with ssDNA and ssRNA, which is an advantageous feature for fluorescence imaging techniques of nucleic acids with longer emission wavelengths than bicyclic thymine (bT).

From the perspective of the preparation of a DNA-based nanowire containing an array of metal ions, DNA-polymerase-catalyzed primer extension reactions were investigated and the formation of up to ten consecutive T-Hg II -T base pairs was achieved by the Hg II -mediated primer extension reaction in the presence of Mn II ions. This enzymatic approach may be one of the promising techniques for preparing a DNA-based metal array.

We designed and synthesized a novel artificial 2'-O,4'-C-methylene bridged nucleic acid (2',4'-BNA/LNA) with a phenoxazine nucleobase and named this compound BNAP. Oligodeoxynucleotide (ODN) containing BNAP showed higher binding affinities toward complementary DNA and RNA as compared to ODNs bearing 2',4'-BNA/LNA with 5-methylcytosine or 2'-deoxyribonucleoside with phenoxazine. Thermodynamic analysis revealed that BNAP exhibits properties associated with the phenoxazine moiety in DNA/DNA duplexes and characteristics associated with the 2',4'-BNA/LNA moiety in DNA/RNA duplexes.

Based on a novel concept, a Reducing-Environment-Dependent Uncatalyzed Chemical Transforming RNA, "REDUCT RNA", we established a post-synthetic approach for the synthesis of 2'-O-methyldithiomethyl-modified oligonucleotides from 2'-O-(2,4,6-trimethoxybenzylthiomethyl)-oligonucleotides by treatment with dimethyl(methylthio)sulfonium tetrafluoroborate. 2'-O-methyldithiomethyl oligonucleotides were easily converted into 2'-hydroxy oligonucleotides under reducing conditions, such as those found in the intracellular environment.

Pentadecamer homopyrimidine oligonucleotides containing three or more 2',5'-phosphodiester linkages in different modes were prepared and used to evaluate the ability as a triplex-forming oligonucleotide (TFO), and it was found that discontinuous replacement of the 3',5'-phosphodiester linkages in TFO by 2',5'-linkages significantly stabilizes parallel-motif triplexes.

Poly(2,7-di-n-pentyldibenzofulvene)s with no stereocenters, obtained by anionic polymerization using chiral 9-fluorenyllithium ligand complexes, showed intense circular dichroism in film form due purely to the chiral conformation of the main chain, while no chiroptical properties were detectable in solution.

5'-Amino-2',4'-BNA, a novel analogue of BNA series compounds, was successfully synthesized, and its incorporated oligonucleotides showed potent duplex- and triplex-forming ability and resistance against snake venom phosphodiesterase.