Abstract
The synthesis and properties of a bridged nucleic acid analogue containing a N30?P50 phosphoramidate linkage, 30-amino-20,40-BNA, is described. A heterodimer containing a 30-amino-20,40-BNA thymine monomer, and thymine and methylcytosine monomers of 30-amino-20,40-BNA and their 50-phosphoramidites, were synthesized efficiently. The dimer and monomers were incorporated into oligonucleotides by conventional 30?50 assembly, and 50?30 reverse assembly phosphoramidite protocols, respectively. Compared to a natural DNA oligonucleotide, modified oligonucleotides containing the 30-amino-20,40-BNA residue formed highly stable duplexes and triplexes with single-stranded DNA (ssDNA), single-stranded RNA (ssRNA), and double-stranded DNA (dsDNA) targets, with the average increase in melting temperature (Tm) against ssDNA, ssRNA and dsDNA being +2.7 to +4.0 C, +5.0 to +7.0 C, and +5.0 to +11.0 C, respectively. These increases are comparable to those observed for 20,40-BNA-modified oligonucleotides. In addition, an oligonucleotide modified with a single 30-amino-20,40-BNA thymine residue showed extraordinarily high resistance to nuclease degradation, much higher than that of 20,40-BNA and substantially higher even than that of 30-amino-DNA and phosphorothioate oligonucleotides. The above properties indicate that 30-amino-20,40-BNA has significant potential for antisense and antigene applications.