The Synthesis and Biological Activity of Organotin Complexes with Thio-Schiff Bases Bearing Phenol Fragments.

A number of novel di- and triorganotin(IV) complexes 1-5 (Ph2SnL1, Ph2SnL2, Et2SnL2, Ph3SnL3, Ph3SnL4) with mono- or dianionic forms of thio-Schiff bases containing antioxidant sterically hindered phenol or catechol fragments were synthesized. Compounds 1-5 were characterized by 1H, 13C NMR, IR spectroscopy, and elemental analysis. The molecular structures of complexes 1 and 2 in the crystal state were established by single-crystal X-ray analysis. The antioxidant activity of new complexes as radical scavengers was estimated in DPPH and ABTS assays. It was found that compounds 4 and 5 with free phenol or catechol fragments are more active in these tests than complexes 1-3 with tridentate O,N,S-coordinated ligands. The effect of compounds 1-5 on the promoted oxidative damage of the DNA by 2,2'-azobis(2-amidinopropane) dihydrochloride and in the process of rat liver (Wistar) homogenate lipid peroxidation in vitro was determined. Complexes 4 and 5 were characterized by more pronounced antioxidant activity in the reaction of lipid peroxidation in vitro than compounds 1-3. The antiproliferative activity of compounds 1-5 was investigated against MCF-7, HTC-116, and A-549 cell lines by an MTT test. The values of IC50 are significantly affected by the presence of free antioxidant fragments and the coordination site for binding.

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O'- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties.

A number of novel heteroligand Zn(II) complexes (1-8) of the general type (Ln)Zn(NN) containing O,N,O'-, O,N,S-donor redox-active Schiff bases and neutral N,N'-chelating ligands (NN) were synthesized. The target Schiff bases LnH2 were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2'-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H2O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H2O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O'- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N'-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV.

Synthesis and Antioxidant Activity of New Catechol Thioethers with the Methylene Linker.

Novel catechol thio-ethers with different heterocyclic substituents at sulfur atom were prepared by reacting 3,5-di-tert-butyl-6-methoxymethylcatechol with functionalized thiols under acidic conditions. A common feature of compounds is a methylene bridge between the catechol ring and thioether group. Two catechols with the thio-ether group, bound directly to the catechol ring, were also considered to assess the effect of the methylene linker on the antioxidant properties. The crystal structures of thio-ethers with benzo-thiazole moieties were established by single-crystal X-ray analysis. The radical scavenging and antioxidant activities were determined using 2,2'-diphenyl-1-picrylhydrazyl radical test, ABTS∙+, CUPRAC (TEAC) assays, the reaction with superoxide radical anion generated by xanthine oxidase (NBT assay), the oxidative damage of the DNA, and the process of lipid peroxidation of rat liver (Wistar) homogenates in vitro. Most catechol-thioethers exhibit the antioxidant effect, which varies from mild to moderate depending on the model system. The dual anti/prooxidant activity characterizes compounds with adamantyl or thio-phenol substituent at the sulfur atom. Catechol thio-ethers containing heterocyclic groups (thiazole, thiazoline, benzo-thiazole, benzo-xazole) can be considered effective antioxidants with cytoprotective properties. These compounds can protect molecules of DNA and lipids from the different radical species.