3lp N]V[R spectroscopy has been used to study the intercalation of the anthracyclines doxorubicin 1, daunorubicin 2, 4-demethoxydaunorubicin 3, morpholinodoxorubicin 4, methoxymorpholinodoxorubicin 5 and 9-deoxydaunorubicin 6 with the DNA fragment d(CGTACG)2. The individual phosphate resonances of the oligonucleotide were assigned in the free as well as in the intercalated species. The 3~p chemical shitt vadations allowed us to identify the intercalation sites, which resulted to be the same for all compounds i e. between the terminal CG base-pairs of the helix (two molecules of drug per duplex). The binding coustants, the dissociation rete constants and AG ~ values have been determined in different conditions of ionic strength and temperature. The kinetic constant (ko~) of the slow step of the anthracycline/duplex intercalation process has been directly measured by NOE exchange techniques. Binding constants depend on the ionic strength and on the self-association process so greatly, that their use to study by NMR anthracycline/DNA interactions is questionable. On the contrary, the kof r are not affected by these phenomena and presentan interesting trend for 1~, thus showing that the average lifetime of the drug in the intercalation site appears to be important for determining the cytotoxicity and the antimitotic activity.

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