Interaction studies of oxindole-derivatives with ß-amyloid peptides inhibiting its aggregation induced by metal ions.

Some hydrazones and Schiff bases derived from isatin, an endogenous oxindole formed in the metabolism of tryptophan, were obtained to investigate their effects on in vitro aggregation of ß-amyloid peptides (Aß), macromolecules implicated in Alzheimer's disease. Some hydrazone ligands, prepared by condensation reactions of isatin with hydrazine derivatives, showed a large affinity binding to the synthetic peptides Aß, particularly to Aß1-16. Measurements by NMR spectroscopy indicated that those interactions occur mainly at the metal binding site of the peptide, involving His6, His13, and His14 residues, and that hydrazone E-diastereoisomer interacts preferentially with the amyloid peptides. Experimental results were consistent with simulations using a docking approach, where it is demonstrated that the amino acid residues Glu3, His6, His13, and His14 are those that mostly interact with the ligands. Further, these oxindole-derived ligands can efficiently chelate copper(II) and zinc(II) ions, forming moderate stable [ML] 1:1 species. The corresponding formation constants were determined by UV/Vis spectroscopy, by titrations of the ligands with increasing amounts of metal salts, and the obtained log K values were in the range 2.74 to 5.11. Both properties, good affinity for amyloid peptides, and reasonably good capacity of chelating biometal ions, like copper and zinc, can explain the efficient inhibition of Aß fragments aggregation, as shown by experiments carried out with the oxindole derivatives in the presence of metal ions.

Platinum(II) complexes containing long-chain hydrophobic N-alkyl-diamine ligands: synthesis, characterization, molecular modeling, and cytotoxic activity.

A series of novel platinum(II) complexes derived from N-alkyl-ethanediamine and N-alkyl-propanediamine ligands were prepared and characterized. These complexes contain a long chain aliphatic diamine where the carbon length is variable and present a hydroxyl group in two different positions. The complexes with the ethanediamine derivatives were prepared from K(2)PtCl(4). Interestingly, the propanediamine derivatives did not react well with this platinum salt under the experimental conditions normally employed and could only be obtained from the more reactive K(2)PtI(4). A theoretical molecular modeling study was performed to understand this difference in reactivity and it showed that the conformation around the diamine plays an important role in the ring closure step of complex formation. The complexes had their cytotoxicity investigated in B16F1, CT26, B16F10, and MDA cell lines. Some of them demonstrated superior activity when compared to cisplatin and carboplatin. We were also able to confirm a structure-activity relationship between cytotoxicity and carbon chain length.