Preparation, characterization and evaluation of novel 1,3,5-triaza-7-phosphaadamantane (PTA)-based palladacycles as anti-cancer agents

Complexes of 2-Amino-3-methylpyridine and 2-Amino-4-methylbenzothiazole with Ag(I) and Cu(II): Structure and Biological Applications

Coordination complexes (1–4) of 2-amino-4-methylbenzothiazole and 2-amino-3-methylpyridine with Cu(CH3COO)2 and AgNO3 were prepared and characterized by UV/Vis and FT-IR spectroscopy. The molecular structure for single crystals of silver complexes (2 and 4) were determined by X-ray diffraction. The coordination complex (2) is monoclinic with space group P21/c, wherein two ligands are coordinated to a metal ion, affording distorted trigonal geometry around the central Ag metal ion. The efficient nucleophilic center, i.e., the endocyclic nitrogen of the organic ligand, binds to the silver metal. Ligands are coordinated to adopt cis arrangement, predominantly due to steric reasons. The O(2) and O(3) atoms of the NO3− group further play an important role in such type of ligand arrangement by hydrogen bonding with the NH2 group of ligands. Complex (4) is orthorhombic, P212121, comprising two molecules of 2-amino-3-methylpyridine as ligand coordinated with the metal ion, affording a polymeric structure. The coordination behavior of the ligand is identical to that in complex 2, wherein ring nitrogen is coordinated to the metal center and bridged to another metal ion through an NH2 group. The resulting product is polymeric in nature with the Ag metal in the backbone and ligand as the bridge. Compounds (2–4) were found to be luminescent, while 1 did not show such activity. All compounds were screened for their preliminary biological activities such as antibacterial, antioxidant and enzyme inhibition. Compounds exhibited moderate activity in these tests.

Mechanistic insights into the anti-cancer activity of the PEGylated binuclear palladacycle, BTC2, against triple-negative breast cancer

Triple-negative breast cancer (TNBC) has a low five-year survival rate, especially if the cancer is diagnosed at a late stage and has already metastasized beyond the breast tissue. Current chemotherapeutic options for TNBC rely on traditional platinum-containing drugs like cisplatin, oxaliplatin and carboplatin. Unfortunately, these drugs are indiscriminately toxic, resulting in severe side effects and the development of drug resistance. Palladium compounds have shown to be viable alternatives to platinum complexes since they are less toxic and have displayed selectivity towards the TNBC cell lines. Here we report the design, synthesis, and characterization of a series of binuclear benzylidene palladacycles with varying phosphine bridging ligands. From this series we have identified BTC2 to be more soluble (28.38-56.77 μg/mL) and less toxic than its predecessor, AJ5, while maintaining its anticancer properties (IC₅₀ (MDA-MB-231) = 0.58 ± 0.012 μM). To complement the previous cell death pathway study of BTC2, we investigated the DNA and BSA binding properties of BTC2 through various spectroscopic and electrophoretic techniques, as well as molecular docking studies. We demonstrate that BTC2 displays multimodal DNA binding properties as both a partial intercalator and groove binder, with the latter being the predominant mode of action. BTC2 was also able to quench the fluorescence of BSA, thereby suggesting that the compound could be transported by albumin in mammalian cells. Molecular docking studies revealed that BTC2 is a major groove binder and binds preferentially to subdomain IIB of BSA. This study provides insight into the influence of the ligands on the activity of the binuclear palladacycles and provides much needed information on the mechanisms through which these complexes elicit their potent anticancer activity.

In Vitro and In Vivo Effect of Palladacycles: Targeting A2780 Ovarian Carcinoma Cells and Modulation of Angiogenesis

Palladacycles are versatile organometallic compounds that show potential for therapeutic use. Here are described the synthesis and characterization of mono- and dinuclear palladacycles bearing diphosphines. Their biological effect was investigated in A2780, an ovarian-derived cancer line, and in normal dermal fibroblasts. The compounds displayed selective cytotoxicity toward the A2780 cell line. Compound 3 decreased the cell viability through cell cycle retention in G0/G1, triggered apoptosis through the intrinsic pathway, and induced autophagy in A2780 cells. Compound 9 also induced cell cycle retention, apoptosis, and cellular detachment. Notably, compound 9 induced the production of intracellular reactive oxygen species (ROS). Our work demonstrated that compound 3 enters A2780 cells via active transport, which requires energy, while compound 9 enters A2780 cells mostly passively. The potential effect of palladacycles in angiogenesis was investigated for the first time in an in vivo chorioallantoic membrane model, showing that while compound 3 displayed an antiangiogenic effect crucial to fighting cancer progression, compound 9 promoted angiogenesis. These results show that palladacycles may be used in different clinical applications where pro- or antiangiogenic effects may be desirable.

Phenylacetylene polymerisation mediated by cationic cyclometallated palladium(ii) complexes bearing benzylidene 2,6-diisopropylphenylamine and its derivatives as ligands

A series of novel cationic palladacycle complexes bearing benzylidene-2,6-diisopropylphenylamine derivatives as ligands and with the general formula [Pd(MeCN)(L)(R-C6H3)CH[double bond, length as m-dash]N{2,6-iPr2-C6H3}][B(3,5-(CF3)2-C6H3)] (R = H, Cl, Br, F, OMe and L = 1,3,5-triaza-7-phosphaadamantane (PTA), tricyclohexylphosphine (PCy3) and triphenylphosphine (PPh3)) were prepared and characterized by a range of analytical techniques. These cationic palladacycle complexes were found to be active precatalysts for the polymerisation of phenylacetylene. The meta-substituent on the cyclometallated ring was found to have a marked effect on the catalyst performance in that complexes, which contained electron-withdrawing substituents, were found to be the most active in the polymerisation process. Furthermore, increasing the steric bulk of the phosphine ligand led to the production of higher molecular weight polyphenylacetylenes (PPA). Polymerisation reactions performed at 25 °C gave a mixture of both cis-transoidal and trans-cisoidal PPA while trans-cisoidal PPA was selectively produced at elevated temperatures (60 °C). Preliminary mechanistic studies demonstrated that polymerisation proceeds via dissociation of the C,N-chelating ligand, and involves the formation of an iminium cationic fragment.