Tetrakis(thione)platinum(II) complexes: synthesis, spectroscopic characterization, crystal structures, and in vitro cytotoxicity

Thermodynamic and kinetic study of palladium(II) complexation with 1-methyl-2-mercaptoimidazole (methimazole) and their importance for structural design of metallodrugs

The acidobasic and complexing properties of 1-methyl-2-mercaptoimidazole (Methimazole, an anti-thyroid drug) were investigated. The pKa 11.49 ± 0.03 was estimated by molecular absorption spectroscopy (I = 0.10 M NaCl, t = 25.0 ± 0.1 °C). This value is in good agreement with the value 11.58 ± 0.05, obtained using the solvent-extraction technique. Theoretical (LFER and quantum chemical calculations) and experimental (1H/13C NMR spectroscopy) methods confirmed that the ligand prefers to be in the thion form, and the proton dissociation takes place on the nitrogen atom. Using glass electrode potentiometry, the complexation of the Pd(II) ion by the methimazole ligand occurs without the participation of protons. The best chemical model considers the [Pd(HL)]2+, [Pd(HL)2]2+ and [Pd(HL)3]2+ complex species, whose stability constants were also determined using spectroscopy and capillary zone electrophoretic (CZE) measurements. The metal complexes dissociate at -log [H+] > 7, where an uncharged palladium(II) hydroxide is formed. The formation kinetics of the palladium(II) complex with methimazole were studied in perchloric and hydrochloric acids (I = 1.00 M, t = 15-40 °C) and the determined rate constants and activation parameters are consistent with literature values determined for the reactions of the Pd(II) ion with thiourea derivatives. The rate constants decrease by two orders of magnitude in both media, which can be assigned to a lower tendency of the chloride ion to dissociate from the [PdCl4]2- complex species than the water molecule from the [Pd(H2O)4]2+ ion. The presented results can be utilized for the design of new Pd and Pt metallodrugs.

1,3-Diazepine: A privileged scaffold in medicinal chemistry

Privileged structures have been widely used as effective templates for drug discovery. While benzo-1,4-diazepine constitutes the first historical example of such a structure, the 1,3 analogue is just as rich in terms of applications in medicinal chemistry. The 1,3-diazepine moiety is present in numerous biological active compounds including natural products, and is used to design compounds displaying a large range of biological activities. It is present in the clinically used anticancer compound pentostatin, in several recent FDA approved β-lactamase inhibitors (e.g., avibactam) and also in coformycin, a natural product known as a ring-expanded purine analogue displaying antiviral and anticancer activities. Several other 1,3-diazepine containing compounds have entered into clinical trials. This heterocyclic structure has been and is still widely used in medicinal chemistry to design enzyme inhibitors, GPCR ligands, and so forth. This review endeavours to highlight the main use of the 1,3-diazepine scaffold and its derivatives, and their applications in medicinal chemistry, drug design, and therapy. We will focus more particularly on the development of enzyme inhibitors incorporating this scaffold, with a strong emphasis on the molecular interactions involved in the inhibition mechanism.