En Route to Osmium Analogues of KP1019: Synthesis, Structure, Spectroscopic Properties and Antiproliferative Activity of <i>trans</i>-[Os^IVCl₄(Hazole)₂]

By controlled Anderson type rearrangement reactions complexes of the general formula <i>trans</i>-[Os^IVCl₄(Hazole)₂], where Hazole = 1<i>H</i>-pyrazole, 2<i>H</i>-indazole, 1<i>H</i>-imidazole, and 1<i>H</i>-benzimidazole, have been synthesized. Note that 2<i>H</i>-indazole tautomer stabilization in <i>trans</i>-[Os^IVCl₄(2<i>H</i>-indazole)₂] is unprecedented in coordination chemistry of indazole. The metal ion in these compounds possesses the same coordination environment as ruthenium(III) in (H₂ind)[Ru^IIICl₄(Hind)₂], where Hind = 1<i>H</i>-indazole, (KP1019), an investigational anticancer drug in phase I clinical trials. These osmium(IV) complexes are appropriate precursors for the synthesis of osmium(III) analogues of KP1019. In addition the formation of an adduct of <i>trans</i>-[Os^IVCl₄(Hpz)₂] with cucurbit[7]uril is described. The compounds have been comprehensively characterized by elemental analysis, EI and ESI mass spectrometry, spectroscopy (IR, UV–vis, 1D and 2D NMR), cyclic voltammetry, and X-ray crystallography. Their antiproliferative acitivity in the human cancer cell lines CH1 (ovarian carcinoma), A549 (nonsmall cell lung carcinoma), and SW480 (colon carcinoma) is reported

En Route to Osmium Analogues of KP1019: Synthesis, Structure, Spectroscopic Properties and Antiproliferative Activity of <i>trans</i>-[Os^IVCl₄(Hazole)₂]

By controlled Anderson type rearrangement reactions complexes of the general formula <i>trans</i>-[Os^IVCl₄(Hazole)₂], where Hazole = 1<i>H</i>-pyrazole, 2<i>H</i>-indazole, 1<i>H</i>-imidazole, and 1<i>H</i>-benzimidazole, have been synthesized. Note that 2<i>H</i>-indazole tautomer stabilization in <i>trans</i>-[Os^IVCl₄(2<i>H</i>-indazole)₂] is unprecedented in coordination chemistry of indazole. The metal ion in these compounds possesses the same coordination environment as ruthenium(III) in (H₂ind)[Ru^IIICl₄(Hind)₂], where Hind = 1<i>H</i>-indazole, (KP1019), an investigational anticancer drug in phase I clinical trials. These osmium(IV) complexes are appropriate precursors for the synthesis of osmium(III) analogues of KP1019. In addition the formation of an adduct of <i>trans</i>-[Os^IVCl₄(Hpz)₂] with cucurbit[7]uril is described. The compounds have been comprehensively characterized by elemental analysis, EI and ESI mass spectrometry, spectroscopy (IR, UV–vis, 1D and 2D NMR), cyclic voltammetry, and X-ray crystallography. Their antiproliferative acitivity in the human cancer cell lines CH1 (ovarian carcinoma), A549 (nonsmall cell lung carcinoma), and SW480 (colon carcinoma) is reported

Osmium(III) Analogues of KP1019: Electrochemical and Chemical Synthesis, Spectroscopic Characterization, X‑ray Crystallography, Hydrolytic Stability, and Antiproliferative Activity

A one-electron reduction of osmium­(IV) complexes <i>trans</i>-[Os^IVCl₄(Hazole)₂], where Hazole = 1<i>H</i>-pyrazole ([<b>1</b>]⁰), 2<i>H</i>-indazole ([<b>2</b>]⁰), 1<i>H</i>-imidazole ([<b>3</b>]⁰), and 1<i>H</i>-benzimidazole ([<b>4</b>]⁰), afforded a series of eight new complexes as osmium analogues of KP1019, a lead anticancer drug in clinical trials, with the general formula (cation)­[<i>trans</i>-Os^IIICl₄(Hazole)₂], where cation = H₂pz⁺ (H₂pz­[<b>1</b>]), H₂ind⁺ (H₂ind­[<b>2</b>]), H₂im⁺ (H₂im­[<b>3</b>]), Ph₄P⁺ (Ph₄P­[<b>3</b>]), <i>n</i>Bu₄N⁺ (<i>n</i>Bu₄N­[<b>3</b>]), H₂bzim⁺ (H₂bzim­[<b>4</b>]), Ph₄P⁺ (Ph₄P­[<b>4</b>]), and <i>n</i>Bu₄N⁺ (<i>n</i>Bu₄N­[<b>4</b>]). All complexes were characterized by elemental analysis, ¹H NMR spectroscopy, electrospray ionization mass spectrometry, UV–vis spectroscopy, cyclic voltammetry, while H₂pz­[<b>1</b>], H₂ind­[<b>2</b>], and <i>n</i>Bu₄[<b>3</b>], in addition, by X-ray diffraction. The reduced species [<b>1</b>]⁻ and [<b>4</b>]⁻ are stable in aqueous media in the absence of air oxygen and do not react with small biomolecules such as amino acids and the nucleotide 5′-dGMP. Cell culture experiments in five different human cancer cell lines (HeLa, A549, FemX, MDA-MB-453, and LS-174) and one noncancerous cell line (MRC-5) were performed, and the results were discussed and compared to those for KP1019 and cisplatin. Benzannulation in complexes with similar structure enhances antitumor activity by several orders of magnitude, implicating different mechanisms of action of the tested compounds. In particular, complexes H₂ind­[<b>2</b>] and H₂bzim­[<b>4</b>] exhibited significant antiproliferative activity <i>in vitro</i> when compared to H₂pz­[<b>1</b>] and H₂im­[<b>3</b>]

X‑ray Absorption Near Edge Structure Spectroscopy to Resolve the in Vivo Chemistry of the Redox-Active Indazolium <i>trans</i>-[Tetrachlorobis(1<i>H</i>‑indazole)ruthenate(III)] (KP1019)

Indazolium <i>trans</i>-[tetrachlorobis­(1<i>H</i>-indazole)­ruthenate­(III)] (<b>1</b>, KP1019) and its analogue sodium <i>trans</i>-[tetrachlorobis­(1<i>H</i>-indazole)­ruthenate­(III)] (<b>2</b>, KP1339) are promising redox-active anticancer drug candidates that were investigated with X-ray absorption near edge structure spectroscopy. The analysis was based on the concept of the coordination charge and ruthenium model compounds representing possible coordinations and oxidation states in vivo. <b>1</b> was investigated in citrate saline buffer (pH 3.5) and in carbonate buffer (pH 7.4) at 37 °C for different time intervals. Interaction studies on <b>1</b> with glutathione in saline buffer and apo-transferrin in carbonate buffer were undertaken, and the coordination of <b>1</b> and <b>2</b> in tumor tissues was studied too. The most likely coordinations and oxidation states of the compound under the above mentioned conditions were assigned. Microprobe X-ray fluorescence of tumor thin sections showed the strong penetration of ruthenium into the tumor tissue, with the highest concentrations near blood vessels and in the edge regions of the tissue samples

Mechanism Elucidation of the <i>cis–trans</i> Isomerization of an Azole Ruthenium–Nitrosyl Complex and Its Osmium Counterpart

Synthesis and X-ray diffraction structures of <i>cis</i> and <i>trans</i> isomers of ruthenium and osmium metal complexes of general formulas (<i>n</i>Bu₄N)­[<i>cis</i>-MCl₄(NO)­(Hind)], where M = Ru (<b>1</b>) and Os (<b>3</b>), and (<i>n</i>Bu₄N)­[<i>trans</i>-MCl₄(NO)­(Hind)], where M = Ru (<b>2</b>) and Os (<b>4</b>) and Hind = 1<i>H</i>-indazole are reported. Interconversion between <i>cis</i> and <i>trans</i> isomers at high temperatures (80–130 °C) has been observed and studied by NMR spectroscopy. Kinetic data indicate that isomerizations correspond to reversible first order reactions. The rates of isomerization reactions even at 110 °C are very low with rate constants of 10^–5 s^–1 and 10^–6 s^–1 for ruthenium and osmium complexes, respectively, and the estimated rate constants of isomerization at room temperature are of ca. 10^–10 s^–1. The activation parameters, which have been obtained from fitting the reaction rates at different temperatures to the Eyring equation for ruthenium [Δ<i>H</i>_{<i>cis‑trans</i>}^‡ <i>=</i> 122.8 ± 1.3; Δ<i><i>H</i></i>_{<i>trans‑cis</i>}^‡ <i>=</i> 138.8 ± 1.0 kJ/mol; Δ<i><i>S</i></i>_{<i>cis‑trans</i>}^‡ <i>=</i> −18.7 ± 3.6; Δ<i><i>S</i></i>_{<i>trans‑cis</i>}^‡ <i>=</i> 31.8 ± 2.7 J/(mol·K)] and osmium [Δ<i>H</i>_{<i>cis‑trans</i>}^‡ <i>=</i> 200.7 ± 0.7; Δ<i><i>H</i></i>_{<i>trans‑cis</i>}^‡ <i>=</i> 168.2 ± 0.6 kJ/mol; Δ<i><i>S</i></i>_{<i>cis‑trans</i>}^‡ <i>=</i> 142.7 ± 8.9; Δ<i><i>S</i></i>_{<i>trans‑cis</i>}^‡ <i>=</i> 85.9 ± 3.9 J/(mol·K)] reflect the inertness of these systems. The entropy of activation for the osmium complexes is highly positive and suggests the dissociative mechanism of isomerization. In the case of ruthenium, the activation entropy for the <i>cis</i> to <i>trans</i> isomerization is negative [−18.6 J/(mol·K)], while being positive [31.0 J/(mol·K)] for the <i>trans</i> to <i>cis</i> conversion. The thermodynamic parameters for <i>cis</i> to <i>trans</i> isomerization of [RuCl₄(NO)­(Hind)]⁻, viz. Δ<i><i>H</i>°</i> = 13.5 ± 1.5 kJ/mol and Δ<i>S</i>° = −5.2 ± 3.4 J/(mol·K) indicate the low difference between the energies of <i>cis</i> and <i>trans</i> isomers. The theoretical calculation has been carried out on isomerization of ruthenium complexes with DFT methods. The dissociative, associative, and intramolecular twist isomerization mechanisms have been considered. The value for the activation energy found for the dissociative mechanism is in good agreement with experimental activation enthalpy. Electrochemical investigation provides further evidence for higher reactivity of ruthenium complexes compared to that of osmium counterparts and shows that intramolecular electron transfer reactions do not affect the isomerization process. A dissociative mechanism of <i>cis</i>↔<i>trans</i> isomerization has been proposed for both ruthenium and osmium complexes

Striking Difference in Antiproliferative Activity of Ruthenium- and Osmium-Nitrosyl Complexes with Azole Heterocycles

Ruthenium nitrosyl complexes of the general formulas (cation)⁺[<i>cis</i>-RuCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (Hind) (<b>1c</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (Hpz) (<b>2c</b>), (cation)⁺ = (H₂bzim)⁺, Hazole = 1<i>H</i>-benzimidazole (Hbzim) (<b>3c</b>), (cation)⁺ = (H₂im)⁺, Hazole = 1<i>H</i>-imidazole (Him) (<b>4c</b>) and (cation)⁺[<i>trans</i>-RuCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>1t</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (<b>2t</b>), as well as osmium analogues of the general formulas (cation)⁺[<i>cis</i>-OsCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (<i>n</i>-Bu₄N)⁺, Hazole =1<i>H</i>-indazole (<b>5c</b>), 1<i>H</i>-pyrazole (<b>6c</b>), 1<i>H</i>-benzimidazole (<b>7c</b>), 1<i>H</i>-imidazole (<b>8c</b>), (cation)⁺ = Na⁺; Hazole =1<i>H</i>-indazole (<b>9c</b>), 1<i>H</i>-benzimidazole (<b>10c</b>), (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>11c</b>), (cation)⁺ = H₂pz⁺, Hazole = 1<i>H</i>-pyrazole (<b>12c</b>), (cation)⁺ = (H₂im)⁺, Hazole = 1<i>H</i>-imidazole (<b>13c</b>), and (cation)⁺[<i>trans</i>-OsCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = <i>n</i>-Bu₄N⁺, Hazole = 1<i>H</i>-indazole (<b>5t</b>), 1<i>H</i>-pyrazole (<b>6t</b>), (cation)⁺ = Na⁺, Hazole = 1<i>H</i>-indazole (<b>9t</b>), (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>11t</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (<b>12t</b>), have been synthesized. The compounds have been comprehensively characterized by elemental analysis, ESI mass spectrometry, spectroscopic techniques (IR, UV–vis, 1D and 2D NMR) and X-ray crystallography (<b>1c</b>·CHCl₃, <b>1t</b>·CHCl₃, <b>2t</b>, <b>3c</b>, <b>6c</b>, <b>6t</b>, <b>8c</b>). The antiproliferative activity of water-soluble compounds (<b>1c</b>, <b>1t</b>, <b>3c</b>, <b>4c</b> and <b>9c</b>, <b>9t</b>, <b>10c</b>, <b>11c</b>, <b>11t</b>, <b>12c</b>, <b>12t</b>, <b>13c</b>) in the human cancer cell lines A549 (nonsmall cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon adenocarcinoma) has been assayed. The effects of metal (Ru vs Os), cis/trans isomerism, and azole heterocycle identity on cytotoxic potency and cell line selectivity have been elucidated. Ruthenium complexes (<b>1c</b>, <b>1t</b>, <b>3c</b>, and <b>4c</b>) yielded IC₅₀ values in the low micromolar concentration range. In contrast to most pairs of analogous ruthenium and osmium complexes known, they turned out to be considerably more cytotoxic than chemically related osmium complexes (<b>9c</b>, <b>9t</b>, <b>10c</b>, <b>11c</b>, <b>11t</b>, <b>12c</b>, <b>12t</b>, <b>13c</b>). The IC₅₀ values of Os/Ru homologs differ by factors (Os/Ru) of up to ∼110 and ∼410 in CH1 and SW480 cells, respectively. ESI-MS studies revealed that ascorbic acid may activate the ruthenium complexes leading to hydrolysis of one M–Cl bond, whereas the osmium analogues tend to be inert. The interaction with myoglobin suggests nonselective adduct formation; i.e., proteins may act as carriers for these compounds

Striking Difference in Antiproliferative Activity of Ruthenium- and Osmium-Nitrosyl Complexes with Azole Heterocycles

Ruthenium nitrosyl complexes of the general formulas (cation)⁺[<i>cis</i>-RuCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (Hind) (<b>1c</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (Hpz) (<b>2c</b>), (cation)⁺ = (H₂bzim)⁺, Hazole = 1<i>H</i>-benzimidazole (Hbzim) (<b>3c</b>), (cation)⁺ = (H₂im)⁺, Hazole = 1<i>H</i>-imidazole (Him) (<b>4c</b>) and (cation)⁺[<i>trans</i>-RuCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>1t</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (<b>2t</b>), as well as osmium analogues of the general formulas (cation)⁺[<i>cis</i>-OsCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = (<i>n</i>-Bu₄N)⁺, Hazole =1<i>H</i>-indazole (<b>5c</b>), 1<i>H</i>-pyrazole (<b>6c</b>), 1<i>H</i>-benzimidazole (<b>7c</b>), 1<i>H</i>-imidazole (<b>8c</b>), (cation)⁺ = Na⁺; Hazole =1<i>H</i>-indazole (<b>9c</b>), 1<i>H</i>-benzimidazole (<b>10c</b>), (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>11c</b>), (cation)⁺ = H₂pz⁺, Hazole = 1<i>H</i>-pyrazole (<b>12c</b>), (cation)⁺ = (H₂im)⁺, Hazole = 1<i>H</i>-imidazole (<b>13c</b>), and (cation)⁺[<i>trans</i>-OsCl₄(NO)­(Hazole)]⁻, where (cation)⁺ = <i>n</i>-Bu₄N⁺, Hazole = 1<i>H</i>-indazole (<b>5t</b>), 1<i>H</i>-pyrazole (<b>6t</b>), (cation)⁺ = Na⁺, Hazole = 1<i>H</i>-indazole (<b>9t</b>), (cation)⁺ = (H₂ind)⁺, Hazole = 1<i>H</i>-indazole (<b>11t</b>), (cation)⁺ = (H₂pz)⁺, Hazole = 1<i>H</i>-pyrazole (<b>12t</b>), have been synthesized. The compounds have been comprehensively characterized by elemental analysis, ESI mass spectrometry, spectroscopic techniques (IR, UV–vis, 1D and 2D NMR) and X-ray crystallography (<b>1c</b>·CHCl₃, <b>1t</b>·CHCl₃, <b>2t</b>, <b>3c</b>, <b>6c</b>, <b>6t</b>, <b>8c</b>). The antiproliferative activity of water-soluble compounds (<b>1c</b>, <b>1t</b>, <b>3c</b>, <b>4c</b> and <b>9c</b>, <b>9t</b>, <b>10c</b>, <b>11c</b>, <b>11t</b>, <b>12c</b>, <b>12t</b>, <b>13c</b>) in the human cancer cell lines A549 (nonsmall cell lung carcinoma), CH1 (ovarian carcinoma), and SW480 (colon adenocarcinoma) has been assayed. The effects of metal (Ru vs Os), cis/trans isomerism, and azole heterocycle identity on cytotoxic potency and cell line selectivity have been elucidated. Ruthenium complexes (<b>1c</b>, <b>1t</b>, <b>3c</b>, and <b>4c</b>) yielded IC₅₀ values in the low micromolar concentration range. In contrast to most pairs of analogous ruthenium and osmium complexes known, they turned out to be considerably more cytotoxic than chemically related osmium complexes (<b>9c</b>, <b>9t</b>, <b>10c</b>, <b>11c</b>, <b>11t</b>, <b>12c</b>, <b>12t</b>, <b>13c</b>). The IC₅₀ values of Os/Ru homologs differ by factors (Os/Ru) of up to ∼110 and ∼410 in CH1 and SW480 cells, respectively. ESI-MS studies revealed that ascorbic acid may activate the ruthenium complexes leading to hydrolysis of one M–Cl bond, whereas the osmium analogues tend to be inert. The interaction with myoglobin suggests nonselective adduct formation; i.e., proteins may act as carriers for these compounds