Hydrophilic Polymers Containing Chiral Nucleic Acid Base Pendants as Polynucleotide Analogs

A survey of our recent work on synthetic polynucleotide analogs is given. Propionic acid and 3-methyl butyric acid derivatives substituted in the 2-position with nucleic acid bases have been used as chiral pendants for attachment to hydrophilic polyamine backbones. Hindered rotation about the amide bonds formed promotes a base-stacked structure as shown by ultraviolet hypochromic effects versus model compounds. If the pendant has been resolved, an optically active polymer results which may be studied by circular dichroism (CD). Thus, poly(ethylenimine) containing the (-)-2-(thymin-l-yl)propionyl group as the grafted pendant showed exciton coupling of the B2u transition of the base chromophores in the CD, as observed in polynucleotides. This implies at least a local helical order in the stacking. The biological activity of such structures is briefly discussed.