Novel C5-Substituted 2′-Deoxyuridine Derivatives Bearing Amino-Linker Arms: Synthesis, Incorporation into Oligodeoxyribonucleotides, and Their Hybridization Properties

2′-Deoxyuridine derivatives bearing several kinds of amino-linker arms at C5 position were synthesized from 5-(methoxycarbonylmethyl)-2′-deoxyuridine and ethylenediamine, 1,6-hexanediamine, or tris(2-aminoethyl)amine. The modified nucleosides were incorporated into oligodeoxyribonucleotides at one or three positions in place of thymidine residues. The thermal stability of the duplexes was investigated. Three incorporations of ethylenediamine or tris(2-aminoethyl)amine at the C5-position increase the duplex stability. The amino-linker arm affected the stability of the duplexes depending on the number of amino groups in the linker arm and the length of the arm. The linker arm improved the nuclease resistance at 5′-side phosphodiester linkage of the modified nucleoside in oligodeoxyribonucleotides.