Binuclear monofunctional platinum(II) complexes formed by hexaazamacrocyclic bisdien ligands: Crystal structure, DNA binding and cytotoxicity studies

Different Modes of Acid-Promoted Cyclooligomerization of 4-(4-Thiosemicarbazido)butan-2-one Hydrazone: 14-Membered versus 28-Membered Polyazamacrocycle Formation

Unprecedented self-assembly of a novel 14-membered cyclic bis-thiosemicarbazone or/and a 28-membered cyclic tetrakis-thiosemicarbazone upon acid-promoted cyclooligomerization of 4-(4-thiosemicarbazido)butan-2-one hydrazone has been discovered. A thorough study of the influence of various factors on the direction of macrocyclization provided the optimal conditions for the highly selective formation of each of the macrocycles in excellent yields. Plausible pathways for macrocyclizations have been discussed. The macrocycle precursor was prepared by the reaction of readily available 4-isothiocyanatobutan-2-one with an excess of hydrazine.

Synthesis, Characterization, and Interaction with Biomolecules of Platinum(II) Complexes with Shikimic Acid-Based Ligands

Starting from the active ingredient shikimic acid (SA) of traditional Chinese medicine and NH₂(CH₂)_nOH, (n = 2–6), we have synthesized a series of new water-soluble Pt(II) complexes PtL^a–eCl₂, where L^a–e are chelating diamine ligands with carbon chain covalently attached to SA (L^a–e = SA-NH(CH₂)_nNHCH₂CH₂NH₂; L^a, n = 2; L^b, n = 3; L^c, n = 4; L^d, n = 5; L^e, n = 6). The results of the elemental analysis, LC-MS, capillary electrophoresis, and ¹H, ¹³C NMR indicated that there was only one product (isomer) formed under the present experimental conditions, in which the coordinate mode of PtL^a–eCl₂ was two-amine bidentate. Their in vitro cytotoxic activities were evaluated by MTT method, where these compounds only exhibited low cytotoxicity towards BEL7404, which should correlate their low lipophilicity. The interactions of the five Pt(II) complexes with DNA were investigated by agarose gel electrophoresis, which suggests that the Pt(II) complexes could induce DNA alteration. We also studied the interactions of the Pt(II) complexes with 5′-GMP with ESI-MS and ¹H NMR and found that PtL^bCl₂, PtL^cCl₂, and PtL^dCl₂ could react with 5′-GMP to form mono-GMP and bis-GMP adducts. Furthermore, the cell-cycle analysis revealed that PtL^bCl₂, PtL^cCl₂ cause cell G₂-phase arrest after incubation for 72 h. Overall, these water-soluble Pt(II) complexes interact with DNA mainly through covalent binding, which blocks the DNA synthesis and replication and thus induces cytotoxicity that weakens as the length of carbon chain increases.

Toxicity in tumor cells, DNA binding mode, and resistance to decomposition by sulfur nucleophiles of new dinuclear bifunctional trans-PtII complexes containing long alkane linkers

In an effort to design dinuclear PtII compounds that maintain the target (DNA) binding profile of the trans-oriented dinuclear bifunctional PtII complexes containing aliphatic linker chains but are less susceptible to metabolic decomposition, the new, long-chain dinuclear PtII complexes—[{trans-PtCl(dien)}2-μ-(CH2)n]2+ (n = 7,10,12, dien = diethylenetriamine)—were synthesized. The toxicity of these metallodrugs was examined in ovarian tumor cell lines. The results showed that the activity of these complexes increased with growing length of the linker; the activity of complex containing the longest linker (n = 12) was comparable with that of cis-diamminedichloridoplatinum(II) (cisplatin). This observation correlated with the results of DNA binding studies performed in cell-free media. The results of these studies demonstrated that the growing length of the aliphatic bridge promoted more distorting conformational alterations induced in DNA. Attention was also paid to the reactivity of {[Pt(dien)Cl]2-alkane} compounds with glutathione (GSH). The results of these experiments support the thesis that the dinuclear structure of {[Pt(dien)Cl]2-alkane} complexes remains stable in the presence of S-containing compounds without undergoing chemical degradation as previously observed for some di/trinuclear bifunctional PtII complexes. This enhanced stability represents a favorable property which may contribute to reduce side effects and increase therapeutic efficacy of the dinuclear {[Pt(dien)Cl]2-alkane} compounds.