Templated synthesis of nylon nucleic acids and characterization by nuclease digestion

Nylon nucleic acids containing oligouridine nucleotides with pendent polyamide linkers and flanked by unmodified heteronucleotide sequences were prepared by DNA templated synthesis. Templation was more efficient than the single-stranded synthesis: Coupling step yields were as high as 99.2%, with up to 7 amide linkages formed in the synthesis of a molecule containing 8 modified nucleotides. Controlled digestion by calf spleen phosphodiesterase enabled the mapping of modified nucleotides in the sequences. A combination of complete degradation of nylon nucleic acids by snake venom phosphodiesterase and dephosphorylation of the resulting nucleotide fragments by bacterial alkaline phosphatase, followed by LCMS analysis, clarified the linear structure of the oligo-amide linkages. The templated synthesis strategy afforded nylon nucleic acids in the target structure and was compatible with the presence heteronucleotides. The complete digestion procedure produced a new species of DNA analogues, nylon ribonucleosides, which display nucleosides attached via a 2'-alkylthio linkage to each diamine and dicarboxylate repeat unit of the original nylon nucleic acids. The binding affinity of a nylon ribonucleoside octamer to the complementary DNA was evaluated by thermal denaturing experiments. The octamer was found to form stable duplexes with an inverse dependence on salt concentration, in contrast to the salt-dependent DNA control.