POLYNUCLEOTIDE ANALOGS .4. SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES OF POLY(DEOXYURIDYLIC ACID) ANALOGS

Poly[(2-uracil-1-yl-2,3-dihydrofuran)-alt-(maleic anhydride)](3)was synthesized by a radical copolymerization of the relevant monomer pair. Its alternating sequence was confirmed by titration of functional groups and the NMR spectrum of the polymer. The number-average molecular weight was found to be 1840, which corresponded to 6.6 repeating units per chain. Hydrolysis of the copolymer gave poly-[(2-uracil-1-yltetrahydrofuran-4,5-diyl)-1,2-dicarboxyethylene] (4), an analogue of poly(2-deoxyuridylic acid) in which the methylene phosphate groups were substituted by dicarboxyethylene groups. Polymer 4 showed a hyperchromicity of 30.1 % in H2O whereas a hypochromicity of 28.4 % in DMF in comparison with the UV absorption of 2'-deoxyuridine. These changes in chromicity were due to base stacking depending on the relative geometry of the stacked chromophores. Consequently, two different conformations of polymer 4 were formed in H2O and in DMF which stayed in equilibrium in solvent mixtures of H2O-DMF. CD and ORD curves of polymer 4 showed several extrema with wavelengths and magnitudes different from those of the monomer. These differences were due to atactic addition polymerization at the dihydrofuran ring of the monomer. Additionally, polymer 4 exhibited a typical polyelectrolyte behavior in the concentration dependence of the reduced viscosity in aqueous solution. The sodium salt of polymer 4 migrated to the anode by electrophoresis and showed three separate bands, indicating that the polymer 4 was a mixture of hepta-, hexa-, and pentamers.