The mechanism of oxidative addition of iodine to a dimethylplatinum(II) complex

Anticancer Activity of Nonpolar Pt(CH3)2I2{bipy} is Found to be Superior among Four Similar Organoplatinum(IV) Complexes

The anticancer properties of well-defined molecules serve to bolster the field of metals in medicine. Such compounds, particularly those of platinum and their closely related structural analogs, continue to be potentially highly interesting to researchers and clinicians alike. The four octahedral organoplatinum(IV) compounds [Pt(CH3)2X2{bipy-R 2 }] (X = Br, I; bipy-R 2 = 2,2'-bipyridine, 2,2'-bipyridine-4,4'-dicarboxylic acid) have been isolated and structurally characterized by single-crystal X-ray diffraction. Nuclear magnetic resonance and infrared spectroscopic data are also tabulated as useful reference values. The anticancer potential of each compound was assessed via in vitro MTT assays, using human breast cancer cells (cell line ZR-75-1). EC50 values were determined as 11.5 μM for Pt(CH3)2Br2{bipy}; 3020 μM, for Pt(CH3)2Br2{bipy-(CO 2 H) 2 }; 6.1 μM, for Pt(CH3)2I2{bipy}; and 86.0 μM, for Pt(CH3)2I2{bipy-(CO 2 H) 2 }; for comparison, the EC50 value for cisplatin against the ZR-75-1 cells was 16.4 μM. The most cytotoxic of the four compounds Pt(CH3)2I2{bipy} undergoes reaction with glutathione in a THF/water mixture at 68°C very slowly.

Supramolecular organometallic chemistry: the platinum(IV) paradigm

Supramolecular chemistry and the chemistry of alkyl derivatives of the transition metals are both topics of considerable current interest, but the combination of the two fields is still underdeveloped. The challenges are, in large part, experimental in nature. For example, the self-assembly of molecules in supramolecular chemistry often relies on intermolecular hydrogen bonding, but most alkyl-transition metal bonds are cleaved by the protic groups used in hydrogen bond formation. Alkyl-platinum(IV) bonds are inert to protonolysis or attack by other electrophiles under mild conditions, and this has allowed an extensive supramolecular chemistry of organoplatinum(IV) complexes to be developed, as outlined in this perspective review. Highlights include a zeolitic structure, a polyrotaxane, a double helix, a nanotube structure and an example of spontaneous resolution to form a chiral sheet structure.

Luminescence studies of new [C,N,N′] cyclometallated platinum(ii) and platinum(iv) compounds

New [C,N,N′]-cyclometallated platinum(ii) and platinum(iv) complexes are prepared and their emission properties are reported.

Supramolecular Polymer and Sheet and a Double Cubane Structure in Platinum(IV) Iodide Chemistry: Solution of a Longstanding Puzzle

The complexes [PtMe₂(L)], L = 2-C₅H₄NCH₂NH-x-C₆H₄OH (x = 2, 3, or 4), react with iodine to form [PtI₂Me₂(L)], by trans oxidative addition, when x = 3 or 4, and they are shown to have polymeric or sheet structures formed through NH···I hydrogen bonding. However, ligand dissociation occurs when x = 2 to give [(PtI₂Me₂) _n ] and, with methyl group transfer, the complex [(PtIMe₃·PtI₂Me₂)₂]. This tetraplatinum cluster complex is shown to have a double cubane structure, thus solving a longstanding puzzle.

Synthesis, characterization and biological activity of new cyclometallated platinum(iv) iodido complexes

The synthesis of six novel cyclometallated platinum(iv) iodido complexes is accomplished by intermolecular oxidative addition of methyl iodide (compounds 2a-2c) or iodine (compounds 3a-3c) upon cyclometallated platinum(ii) compounds [PtX{(CH₃)₂N(CH₂)₃NCH(4-ClC₆H₃)}] (1a-1c: X = Cl, CH₃ or I). The X-ray molecular structures of platinum(ii) compound 1c and platinum(iv) compounds 3b and 3a' (an isomer of 3a) are reported. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), DNA interaction, topoisomerase I, IIα, and cathepsin B inhibition, and cell cycle arrest, apoptosis and ROS generation of the investigated complexes are presented. Remarkable antiproliferative activity was observed for most of the synthesized cycloplatinated compounds (series 1-3) in all the selected carcinoma cell lines. The best inhibition was provided for the octahedral platinum(iv) compounds 2a-2c exhibiting a methyl and an iodido axial ligand. Preliminary biological results point to a different mechanism of action for the investigated compounds. Cyclometallated platinum(ii) compounds 1a-1c modify the DNA migration as cisplatin. In contrast, cyclometallated platinum(iv) compounds 2a-2c and 3a-3c did not modify the DNA tertiary structure neither in the absence nor in the presence of ascorbic acid, which made them incapable of reducing platinum(iv) compounds 2b and 2c in a buffered aqueous medium (pH 7.40) according to ¹H NMR experiments. Remarkable topoisomerase IIα inhibitory activity is reported for platinum(iv) complexes 2b and 3a and in addition, for the last one, a moderate cathepsin B inhibition is reported. Cell cycle arrest (decrease in G0/G1 and G2 phases and arrest in the S phase), induction of apoptosis and ROS generation are related to the antiproliferative activity of some representative octahedral cyclometallated platinum(iv) compounds (2b and 2c).

Shedding Light on the Nature of Photoinduced States Formed in a Hydrogen-Generating Supramolecular RuPt Photocatalyst by Ultrafast Spectroscopy

Photoinduced electronic and structural changes of a hydrogen-generating supramolecular RuPt photocatalyst are studied by a combination of time-resolved photoluminescence, optical transient absorption, and X-ray absorption spectroscopy. This work uses the element specificity of X-ray techniques to focus on the interplay between the photophysical and -chemical processes and the associated time scales at the catalytic Pt moiety. We observe very fast (<30 ps) photoreduction of the Pt catalytic site, followed by an ∼600 ps step into a strongly oxidized Pt center. The latter process is likely induced by oxidative addition of reactive iodine species. The oxidized Pt species is long-lived and fully recovers to the original ground state complex on a >10 μs time scale. However, the photosensitizing Ru moiety is fully restored on a much shorter ∼300 ns time scale. This reaction scheme implies that we may withdraw two electrons from a catalyst that is activated by a single photon.

Synthesis, characterization and biological activity of new cyclometallated platinum(iv) complexes containing a para-tolyl ligand

The synthesis of three new cyclometallated platinum(ii) compounds containing a para-tolyl ligand and a tridentate [C,N,N'] (cm1) or a bidentate [C,N] ligand and an additional ligand such as SEt2 (cm2) or PPh3 (cm3) is reported. The X-ray molecular structure of platinum(ii) compound cm3 is also presented. Intermolecular oxidative addition of methyl iodide or iodine upon cm1, cm2 and cm3 produced six novel cyclometallated platinum(iv) compounds. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), DNA interaction, topoisomerase I, IIα, and cathepsin B inhibition, and cell cycle arrest, apoptosis and ROS generation of the investigated complexes are presented. The best results for antiproliferative activity were obtained for platinum(iv) compounds cm1MeI and cm1I2 arising from oxidative addition of methyl iodide and iodine, respectively, to cm1. Cyclometallated platinum(iv) compounds cm1MeI and cm3MeI induce significant changes in the mobility of DNA and, in addition, cm1MeI, cm3MeI and cm1I2, showed considerable topoisomerase IIα inhibitory activity. Moreover, the compounds exhibiting the higher antiproliferative activity (cm1MeI and cm1I2) were found to generate ROS and to supress HCT-116 colon cancer cell growth by a mixture of cell cycle arrest and apoptosis induction. 1H NMR experiments carried out in a buffered aqueous medium (pH 7.40) indicate that compound cm1MeI is not reduced by common biologically relevant reducing agents such as ascorbic acid, glutathione or cysteine.

Oxidation of Half-Lantern Pt2(II,II) Compounds by Halocarbons. Evidence of Dioxygen Insertion into a Pt(III)-CH3 Bond

The half-lantern compound [{Pt(bzq)(μ-N^S)}2] (1) [bzq = benzo[h]quinoline, HN^S = 2-mercaptopyrimidine (C4H3N2HS)] reacts with CH3I and haloforms CHX3 (X = Cl, Br, I) to give the corresponding oxidized diplatinum(III) derivatives [{Pt(bzq)(μ-N^S)X}2] (X = Cl 2a, Br 2b, I 2c). These compounds exhibit half-lantern structures with short intermetallic distances (∼2.6 Å) due to Pt-Pt bond formation. The halogen abstraction mechanisms from the halocarbon molecules by the Pt2(II,II) compound 1 were investigated. NMR spectroscopic evidence using labeled reagents support that in the case of (13)CH3I the reaction initiates with an oxidative addition through an SN2 mechanism giving rise to the intermediate species [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}]. However, with haloforms the reactions proceed through a radical-like mechanism, thermally (CHBr3, CHI3) or photochemically (CHCl3) activated, giving rise to mixtures of species [X(bzq)Pt(μ-N^S)2Pt(bzq)R] (3a-c) and [X(bzq)Pt(μ-N^S)2Pt(bzq)X] (2a-c). In these cases the presence of O2 favors the formation of species 2 over 3. Transformation of 3 into 2 was possible upon irradiation with UV light. In the case of [I(bzq)Pt(μ-N^S)2Pt(bzq)((13)CH3)}] (3d), in the presence of O2 the formation of the unusual methylperoxo derivative [I(bzq)Pt(μ-N^S)2Pt(bzq)(O-O(13)CH3)}] (4d) was detected, which in the presence of (13)CH3I rendered the final product [{Pt(bzq)(μ-N^S)I}2] (2c) and (13)CH3OH.

Oxidation of dimethylplatinum(II) complexes with malonyl peroxide derivatives

The reaction of the cyclic peroxides cyclobutane malonoyl peroxide and cyclopentane malonoyl peroxide to dimethylplatinum(II) complexes with the bidentate nitrogen donor ligand 4,4′-di-t-butyl-2,2′-bipyridine (bubpy) gave a mixture of the products of cis and trans oxidative addition, [PtMe2{(O2C)2C(C3H6)}(bubpy)] and [PtMe2{(O2C)2C(C4H8)}(bubpy)], respectively. The cis isomers exist with a chelating dicarboxylate ligand, forming a six-membered ring, while the trans isomers are thought to exist as oligomers, which may react with water or solvent to give complexes containing a monodentate dicarboxylate ligand. Equilibration of the product of cis oxidative addition, cis-[PtMe2{(O2C)2C(C3H6)}(bubpy)], with oxalic or phthalic acid to give equilibria with the oxalate cis-[PtMe2(O4C2)(bubpy)] or phthalate cis-[PtMe2{(O2C)2C6H4}(bubpy)] derivative, respectively, indicated the expected sequence of chelate stability oxalate > cyclobutane malonate > phthalate.