Synthesis of linear poly(ethylenimine) containing nucleic acid pendants as polynucleotide analogs

Polynucleotide analogs with a linear poly(ethylenimine) (PEI) backbone and adenine, cytosine, and hypoxanthine pendants were synthesized. Linear PEI was synthesized by the cationic ring‐opening polymerization of 2‐H‐2‐oxazoline, followed by acid hydrolysis. 2‐(Adenin‐9‐yl)‐ and 2‐(N6‐benzyladenin‐9‐yl)‐, 2‐(cytosin‐1‐yl)propanoic acids in addition to 2‐(adenin‐9‐yl)‐3‐methyland 3‐(cytosin‐1‐yl)butanoic acids were synthesized from their respective nucleic acid bases. 2‐(Hypoxanthin‐9‐yl)propanoic acid and 3‐(hypoxanthin‐9‐yl)butanoic acid were converted from the corresponding adenine derivatives by reaction with nitrous acid. Grafting reactions of pendant groups onto various molecular weight PEI backbones were carried out at room temperature, using the coupling agent norborn‐5‐ene‐2,3‐carboximido diphenyl phosphate (PPONB), generally resulting in percent graft values greater than 90%. PPONB showed selectivity against the amino group of adenine and cytosine rings. The appropriate model compounds were also prepared.