Abstract
3-nitro-9-[2-(dialkylamino)ethyl)]aminoacridines (alkyl = methyl or ethyl) have been used as ligands towards platinum(If). The end product is a complex in which the acridine acts as a tridentate ligand contributing the two exocyclic nitrogen atoms and one of the two peri carbons. The metallation takes place predominantly at the peri position of the unsubstituted ring. The coordinated acridine is in the imino tautomeric form although, in the free state, it occurs exclusively in the amino form (both in the solid state and in solution). The imino tautomer is considered to be the biologically active form. In the platinated species the N(10)H of the acridine can be involved in strong hydrogen bonding with a chloride ion leading to formation of an association complex, the formation constant has been found to be 1.4±103 M−1. The N(10)H┄CI interaction can influence the tautomeric equilibrium of the acridine dye also in the uncoordinated species, however, the shift in favor of the imino tautomer is not complete.
Highlights
Acridines are interesting molecules well known for their DNA intercalating abilities and for the pharmacological properties they can develop in the presence of appropriate substituents
A 0.8 mL solution (1.4 mM) of the metallated platinum compound, placed in a NMR tube, was treated with aliquots of tetrabutylammonium chloride and the H NMR spectrum recorded after each addition
Since la always co-crystallizes with some acetone, the N(10)H chemical shift, at zero acetone content, was evaluated by extrapolation to zero of a quasi linear plot reporting the chemical shift of N(10)H against the content of acetone
Summary
Acridines are interesting molecules well known for their DNA intercalating abilities and for the pharmacological properties they can develop in the presence of appropriate substituents. EPR and laser flash photolysis experiments have shown that photo-excited quinacrine is a producer of superoxide and hydroperoxy adducts and that quinacrine photoproducts produce singlet oxygen, rendering the molecule a candidate for photodynamic therapy/6/. Both the above quoted acridines share the presence of a diamino alkyl chain stemming from C(9). The presence and the position of substituents in the acridine ring system are crucial for the biological activity of these compounds. Isomers of nitracrine-WHO, having the nitro group in ring positions other than 1, completely lose the antitumor activity. The efficacy is related to the number of methylene spacers
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