Heterochiral DNA with Complementary Strands in α-D and β-D Configuration: H-Bonded and Silver Mediated Base Pairs with Impact of 7-Deazapurines Replacing Purines.

Heterochiral DNA with H-bonded and silver mediated base pairs was constructed using complementary strands with nucleosides in α-D or β-D configuration. Anomeric phosphoramidites were employed to assemble oligonucleotides. According to T m values and thermodynamic data duplex stability of 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 confirming Watson-Crick type base pairing. When cytosine was facing cytosine, thymine or adenine residues duplex DNA formed silver mediated base pairs. Whereas CD spectra of single strands with α-D configuration display mirror like shapes to those with β-configuration the CD spectra of H-bonded duplexes and those with a limited number of silver pairs form a B-type double helix almost indistinguishable from natural DNA. Non-melting silver ion-DNA complexes with entirely different CD spectra are generated when the silver ions equal the number of base pairs.