Conformational Isomerism of trans-[Pt(NH2C6H11)2I2] and the Classical Wernerian Chemistry of [Pt(NH2C6H11)4]X2 (X = Cl, Br, I)

E- or Z-Isomers Arising from the Geometries of Ligands in the Mercury Complex of 2-(Anthracen-9-ylmethylene)-N-phenylhydrazine Carbothioamide

An anionic mercury(II) complex of 2-(anthracen-9-ylmethylene)-N-phenylhydrazine carbothioamide (HATU) and two isomers of a neutral mercury(II) complex of the anion of the same ligand (ATU) were reported. The anionic complex [Hg(HATU)2Cl2]·CH2Cl2 had a monodentate HATU ligand (a neutral form of the ligand) and chloride ligands. The two conformational isomers were of the neutral mercury(II) complex Hg(ATU)2·2DMF. The two isomers were from the E or Z geometry of the ligands across the conjugated C=N-N=C-N scaffold of the coordinated ligand. The two isomers of the complex were independently prepared and characterized. The spectroscopic properties of the isomers in solution were studied by 1H NMR as well as fluorescence spectroscopy. Facile conversion of the E-isomer to the Z-isomer in solution was observed. Density functional theory (DFT) calculations revealed that the Z-isomer of the complex was stable compared to the E-isomer by an energy of 14.35 kJ/mol; whereas, E isomer of the ligand was more stable than Z isomer by 8.37 KJ/mol. The activation barrier for the conversion of the E-isomer to the Z-isomer of the ligand was 167.37 kJ/mol. The role of the mercury ion in the conversion of the E-form to the Z-form was discussed. The mercury complex [Hg(HATU)2Cl2]·CH2Cl2 had the E-form of the ligand. Distinct photophysical features of these mercury complexes were presented.

Palladium Complexes of Corroles and Sapphyrins

Palladium complexes of corrole and sapphyrin were prepared in high yield and fully characterized. The corrole provides a tetradentate/trianionic square planar coordination sphere for Pd^II , charge balanced by pyridinium. Both one and two Pd^II ions may be accommodated by the pentapyrrolic skeleton of the sapphyrin, and in each case the macrocycle acts as bidentate/monoanionic ligand and the inner-sphere square planar geometry is completed by allyl anions coordinated in an η³ fashion. NMR spectroscopy and X-ray crystallography data analyses uncovered the presence of interesting stereoisomers due to the flexibility of the ally ligands and also the pyrrole ring(s) that is/are not involved in metal binding.

The Next Generation of Platinum Drugs: Targeted Pt(II) Agents, Nanoparticle Delivery, and Pt(IV) Prodrugs

The platinum drugs, cisplatin, carboplatin, and oxaliplatin, prevail in the treatment of cancer, but new platinum agents have been very slow to enter the clinic. Recently, however, there has been a surge of activity, based on a great deal of mechanistic information, aimed at developing nonclassical platinum complexes that operate via mechanisms of action distinct from those of the approved drugs. The use of nanodelivery devices has also grown, and many different strategies have been explored to incorporate platinum warheads into nanomedicine constructs. In this Review, we discuss these efforts to create the next generation of platinum anticancer drugs. The introduction provides the reader with a brief overview of the use, development, and mechanism of action of the approved platinum drugs to provide the context in which more recent research has flourished. We then describe approaches that explore nonclassical platinum(II) complexes with trans geometry or with a monofunctional coordination mode, polynuclear platinum(II) compounds, platinum(IV) prodrugs, dual-threat agents, and photoactivatable platinum(IV) complexes. Nanoparticles designed to deliver platinum(IV) complexes will also be discussed, including carbon nanotubes, carbon nanoparticles, gold nanoparticles, quantum dots, upconversion nanoparticles, and polymeric micelles. Additional nanoformulations, including supramolecular self-assembled structures, proteins, peptides, metal-organic frameworks, and coordination polymers, will then be described. Finally, the significant clinical progress made by nanoparticle formulations of platinum(II) agents will be reviewed. We anticipate that such a synthesis of disparate research efforts will not only help to generate new drug development ideas and strategies, but also will reflect our optimism that the next generation of approved platinum cancer drugs is about to arrive.

Improvements in the Synthesis and Understanding of the Iodo-bridged Intermediate en Route to the Pt(IV) Prodrug Satraplatin

Mixed amine/ammine motifs are important features in newer generation platinum anticancer agents, including the Pt(IV) prodrug satraplatin. One synthetic route that can be used to access platinum molecules with such structures exploits the trans effect during NH3-mediated cleavage of iodo-bridged platinum(II) dimers of the form [Pt(Am)I(μ-I)]2, where Am is an amine. A clear picture of the nature of these dimers that is consistent with the reactivity they exhibit has remained elusive. Moreover, technical aspects of this chemistry have impeded its more widespread use. We present here an improved strategy that permits isolation and use of [Pt(Am)I(μ-I)]2, where Am is cyclohexylamine, within minutes as opposed to weeks, as previously reported. A detailed spectroscopic, crystallographic, and chromatographic investigation of this intermediate in the synthesis of satraplatin is also presented with a discussion of the ability of both cis and trans isomers of the dimer to produce exclusively cis-[Pt(NH2C6H11)(NH3)I2] upon treatment with NH3.

The chiral potential of phenanthriplatin and its influence on guanine binding

The monofunctional platinum complex cis-[Pt(NH3)2Cl(Am)](+), also known as phenanthriplatin, where Am is the N-heterocyclic base phenanthridine, has promising anticancer activity. Unlike bifunctional compounds such as cisplatin, phenanthriplatin can form only one covalent bond to DNA. Another distinguishing feature is that phenanthriplatin is chiral. Rotation about the Pt-N bond of the phenanthridine ligand racemizes the complex, and the question arises as to whether this process is sufficiently slow under physiological conditions to impact its DNA-binding properties. Here we present the results of NMR spectroscopic, X-ray crystallographic, molecular dynamics, and density functional theoretical investigations of diastereomeric phenanthriplatin analogs in order to probe the internal dynamics of phenanthriplatin. These results reveal that phenanthriplatin rapidly racemizes under physiological conditions. The information also facilitated the interpretation of the NMR spectra of small molecule models of phenanthriplatin-platinated DNA. These studies indicate, inter alia, that one diastereomeric form of the complexes cis-[Pt(NH3)2(Am)(R-Gua)](2+), where R-Gua is 9-methyl- or 9-ethylguanine, is preferred over the other, the origin of which stems from an intramolecular interaction between the carbonyl oxygen of the platinated guanine base and a cis-coordinated ammine. The relevance of this finding to the DNA-damaging properties of phenanthriplatin and its biological activity is discussed.