Heterochiral DNA with Complementary Strands with alpha-dand beta-dConfigurations: Hydrogen-Bonded and Silver-Mediated Base Pairs with Impact of 7-Deazapurines Replacing Purines

Abstract

Heterochiral DNA with hydrogen-bonded and silver-mediated base pairs have been constructed using complementary strands with nucleosides with alpha-dor beta-dconfiguration. Anomeric phosphoramidites were employed to assemble the oligonucleotides. According to theT(m)values and thermodynamic data, the duplex stability of the heterochiral duplexes was similar to that of homochiral DNA, but mismatch discrimination was better in heterochiral DNA. Replacement of purines by 7-deazapurines resulted in stable parallel duplexes, thereby confirming Watson-Crick-type base pairing. When cytosine was facing cytosine, thymine or adenine residues, duplex DNA formed silver-mediated base pairs in the presence of silver ions. Although the CD spectra of single strands with alpha-dconfiguration display mirror-like shapes to those with the beta-dconfiguration, the CD spectra of the hydrogen-bonded duplexes and those with a limited number of silver pairs show a B-type double helix almost indistinguishable from natural DNA. Nonmelting silver ion-DNA complexes with entirely different CD spectra were generated when the number of silver ions was equal to the number of base pairs.