Synthesis of polynucleotide analogs by grafting optically active nucleic acid base derivatives onto polyethylenimine

Polynucleotide analogs with a polyethylenimine backbone and optically active thymine- and adenine-containing pendants and their model compounds were synthesized. The pendants were prepared by the addition reaction of the nucleic acid base to ethyl crotonate. The ammonium salt of 3-(adenin-9-yl)butyric acid was employed to replace its free acid for the formation of diastereomeric salt with brucine. Fractional crystallization of the diastereomeric salt generates the partially resolved enantiomers. The solubility difference between the racemic mixture and its enantiomer was utilized to obtain the pure enantiomers. The active esters of the pendants were prepared. Grafting reactions were carried out by the reaction of active esters with PEI at room temperature. Completely grafted polymers were obtained.