The first study of the interaction of tin() with the anticancer antibiotic doxorubicin in N,N-dimethylformamide (dmf) solution is reported. Electronic absorption spectroscopy showed that reaction of the drug with SnCl 4 is time dependent and involves the initial formation of a 1 : 1 complex. The strong binding was also shown by 119 Sn NMR spectroscopy. Reactions with modified anthracyclines show that the α-ketol side chain at C 9 is essential for interaction, while the quinone chromophore is not involved in binding, as inferred from optical spectroscopy. Proton NMR data suggest that binding to the C 9 side chain involves enolization at C 13 -C 14 . The two-dimensional total correlation spectra indicate that the daunosamine moiety of doxorubicin can be involved in Sn IV binding with formation of several time-dependent species. This was verified by 1 H and 119 Sn NMR studies of Sn IVdaunosaminide hydrochloride systems. These findings suggest that Sn IV can bind to doxorubicin at two sites: the C 9 α-ketol chain, probably after enolization, and the sugar ring at the 4Ј-OH and 3Ј-NH 2 positions. This is the first report of metal binding to doxorubicin at the C 9 side chain.

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