Dimerization of coralyne and its propyl analogue and their association with DNA.

Dimerization of coralyne, Ia, and its propyl analogue Ic has been analyzed at neutral pH as a function of ionic strength. Even at low ionic strength (I = 0.02) dimerization constants (molar units) for both compounds are 10(5) or greater, which is considerably larger than values obtained for similar intercalating molecules. Coralyne seems to undergo association to higher aggregates somewhat easier than Ic, which could be due to the fact that the propyl group on Ic provides some steric hinderance in forming higher aggregates. Both compounds readily associate with DNA. At high ratios of ligand to DNA, the spectra for Ia or Ic are similar to that of a highly aggregated complex. At low ratios of ligand to DNA, the spectra for both compounds approach a limit, which is relatively independent of ionic strength and concentration, and can be identified with the intercalated species. The slight differences between Ia and Ic in dimerization or in association with DNA do not seem capable of explaining the significant differences in antileukemic activity of these compounds.