Chemistry and biological activity of platinum amidine complexes

Synthesis, characterization, and antibacterial activities of a heteroscorpionate derivative platinum complex against methicillin-resistant Staphylococcus aureus

Staphylococcus aureus is one of the species with the greatest clinical importance and greatest impact on public health. In fact, methicillin-resistant S. aureus (MRSA) is considered a pandemic pathogen, being essential to develop effective medicines and combat its rapid spread. This study aimed to foster the translation of clinical research outcomes based on metallodrugs into clinical practice for the treatment of MRSA. Bearing in mind the promising anti-Gram-positive effect of the heteroscorpionate ligand 1,1’-(2-(4-isopropylphenyl)ethane-1,1-diyl)bis(3,5-dimethyl-1H-pyrazole) (2P), we propose the coordination of this compound to platinum as a clinical strategy with the ultimate aim of overcoming resistance in the treatment of MRSA. Therefore, the novel metallodrug 2P-Pt were synthetized, fully characterized and its antibacterial effect against the planktonic and biofilm state of S. aureus evaluated. In this sense, three different strains of S. aureus were studied, one collection strain of S. aureus sensitive to methicillin and two clinical MRSA strains. To appraise the antibacterial activity, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC), and minimum biofilm eradication concentration (MBEC) were determined. Moreover, successful outcomes on the development of biofilm in a wound-like medium were obtained. The mechanism of action for 2P-Pt was proposed by measuring the MIC and MBC with EDTA (cation mediated mechanism) and DMSO (exogenous oxidative stress mechanism). Moreover, to shed light on the plausible antistaphylococcal mechanism of this novel platinum agent, additional experiments using transmission electron microscopy were carried out. 2P-Pt inhibited the growth and eradicated the three strains evaluated in the planktonic state. Another point worth stressing is the inhibition in the growth of MRSA biofilm even in a wounded medium. The results of this work support this novel agent as a promising therapeutic alternative for preventing infections caused by MRSA.

Nickel(ii)-mediated cyanamide–pyrazole coupling highlights distinct reactivity of NCNR2 and NCR nitrile ligands

The nickel(ii) center efficiently promotes the cyanamide–pyrazole coupling to give bis-chelate and tris-chelate products. The formation of the tris-chelate product for dialkylcyanamides is thermodynamically favorable.

Nucleophilic addition reactions to the ethylnitrilium derivative of nido-carborane 10-EtCN-7,8-C2B9H11

Stable imidates 10-EtC(OR)HN-7,8-C₂B₉H₁₁ and thioimidates 10-EtC(SR)HN-7,8-C₂B₉H₁₁ were synthesized via the reactions of a nitrilium derivative of nido-carborane 10-EtCN-7,8-C₂B₉H₁₁ with alcohols and thiols.

Metal-Involving Synthesis and Reactions of Oximes

This review classifies and summarizes the past 10-15 years of advancements in the field of metal-involving (i.e., metal-mediated and metal-catalyzed) reactions of oximes. These reactions are diverse in nature and have been employed for syntheses of oxime-based metal complexes and cage-compounds, oxime functionalizations, and the preparation of new classes of organic species, in particular, a wide variety of heterocyclic systems spanning small 3-membered ring systems to macroheterocycles. This consideration gives a general outlook of reaction routes, mechanisms, and driving forces and underlines the potential of metal-involving conversions of oxime species for application in various fields of chemistry and draws attention to the emerging putative targets.

Palladium-catalyzed three-component reaction of N-tosyl hydrazones, isonitriles and amines leading to amidines

A palladium-catalyzed three-component reaction between N-tosyl hydrazones, aryl isonitriles and amines was developed, leading to amidines in moderate to good yields. This procedure features the rapid construction of amidine frameworks with high diversity and complexity. Ketenimines serve as intermediates, which encounter nucleophilic attack by amines to produce amidines.

Coupling of platinated triguanides with platinum-activated nitriles as a novel strategy for generation of dimetallic systems

One of two Pt(IV)-activated propanenitriles in trans-[PtCl4(EtCN)2] is involved in platinum(IV)-mediated nitrile-imine coupling with the platinum(II)-based metallacycles [PtCl2{NH=C(NR2)N(Ph)C(=NH)N(Ph)C(NR2)=NH}] [R2 = Me2 (1a), C5H10 (1b)] yielding diplatinum products, whose structures depend on molar ratios between the reactants. At a 1 : 1 ratio, the mixed-valence platinum(II)/platinum(IV) species [PtCl4{NH=C(NR2)N(Ph)C{=[(N(Et)C=NH)PtCl2(EtCN)]}N(Ph)C(NR2)=NH}] [R2 = Me2 (2a), (CH2)5 (2b)] were generated, whereas at a 1 : 2 ratio the dinuclear platinum(II)/platinum(II) complexes [PtCl2{NH=C(NR2)N(Ph)C{=[(N(Et)C=NH)PtCl2(EtCN)]}N(Ph)C(NR2)=NH}] [R2 = Me2 (3a), (CH2)5 (3b)] were obtained. In contrast to the nitrile-imine coupling observed for the platinum(IV) dinitrile complex, the reaction between the platinum(II) congener trans-[PtCl2(EtCN)2] and any one of 1a,b gives exclusively the substituted dimetallic platinum(II)/platinum(II) products [PtCl2{NH=C(NR2)N(Ph)C{=[(NH)PtCl2(EtCN)]}N(Ph)C(NR2)=NH}] [R2 = Me2 (6a), (CH2)5 (6b)] featuring platinum-containing guanidine 1 as one of the ligands. Complexes 2a,b, 3a,b, and 6a,b were characterized by elemental analyses (C, H, N), HRESI-MS, IR, (1)H NMR spectroscopy, and DTA/TG. The molecular and crystal structure of 2a·2CDCl3 was additionally studied by single-crystal X-ray diffraction. Complexes 2a,b undergo further redox transformation in solutions, and single crystals of [PtCl2{NH=C(NMe2)N(Ph)C{=[(N(Et)C=NH)PtCl2(MeCN)]}N(Ph)C(NMe2)=NH}]·2CH2Cl2 (3'a·2CH2Cl2) were obtained from 2a in a CH2Cl2-MeCN-C2H4Cl2 mixture and studied by X-ray crystallography. The driving forces for the generation of diplatinum products 2 and 3 were elucidated based on a quantum-chemical study.

Design of enzymatically cleavable prodrugs of a potent platinum-containing anticancer agent

Using a versatile synthetic approach, a new class of potential ester prodrugs of highly potent, but systemically too toxic, platinum-acridine anticancer agents was generated. The new hybrids contain a hydroxyl group, which has been masked with a cleavable lipophilic acyl moiety. Both butanoic (butyric) and bulkier 2-propanepentanoic (valproic) esters were introduced. The goals of this design were to improve the drug-like properties (e.g., logD) and to reduce the systemic toxicity of the pharmacophore. Two distinct pathways by which the target compounds undergo effective ester hydrolysis, the proposed activating step, have been confirmed: platinum-assisted, self-immolative ester cleavage in a low-chloride environment (LC-ESMS, NMR spectroscopy) and enzymatic cleavage by human carboxylesterase-2 (hCES-2) (LC-ESMS). The valproic acid ester derivatives are the first example of a metal-containing agent cleavable by the prodrug-converting enzyme. They show excellent chemical stability and reduced systemic toxicity. Preliminary results from screening in lung adenocarcinoma cell lines (A549, NCI-H1435) suggest that the mechanism of the valproic esters may involve intracellular deesterification.

Novel (cyanamide)ZnIIcomplexes and zinc(ii)-mediated hydration of the cyanamide ligands

The Zn^II-mediated hydration of cyanamides does not require any co-catalyst.

Guanidine platinum(II) complexes: synthesis, in vitro antitumor activity, and DNA interactions

The novel guanidine compounds trans-[Pt(NH₂Me)₂{NH=C(NHMe)NR}₂](Cl)₂ (R = NEt₂ [7], NC₅H₁₀ [8]) (trans-7,8) were synthesized by the nucleophilic addition of methylamine to dialkylcyanamide ligands of the push–pull nitrile complexes trans-[PtCl₂(RCN)₂] (R = NEt₂, NC₅H₁₀). In vitro cytotoxicity tests conducted for the entire series of the guanidine complexes, i.e. trans-7,8, the neutral cis- or trans-[PtCl₂{NH=C(NH₂)R}₂] (cis-1–3 and trans-1–3) and the cationic cis- or trans-[Pt(NH₃)₂{NH=C(NH₂)R}₂](Cl)₂ (cis-4–6 and trans-4–6) (R = NMe₂ [1,4], NEt₂ [2,5], NC₅H₁₀ [3,6]) in two human cancer cell lines, CH1 (ovarian carcinoma) and SW480 (colon cancer), confirmed that the cytotoxicity of several trans-configured (trans-3,6) complexes is higher than that of cis-congeners (cis-3,6). Cellular platinum levels were analyzed by inductively coupled plasma mass spectrometry upon treatment of SW480 cells, revealing a dependence of cellular accumulation on the geometrical isomerism and the steric hindrance of the variable substituent R on the guanidine ligand. DNA interactions of selected guanidine complexes were studied in order to find hints for the possible reasons for their different activities. Changes induced to the electrophoretic mobility of a dsDNA plasmid confirmed the potency of the guanidine complexes (e.g. trans-1,3,5,6 and cis-1,3,4) to significantly alter DNA secondary structure, indicating DNA as a possible critical target of these compounds.

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A series of guanidine–Pt(II) complexes was extended with two new compounds.

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Structure–activity relationships were inferred from cell culture studies.

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New examples of active platinum complexes with trans geometry were identified.

Dialkylcyanamides are more reactive substrates toward metal-mediated nucleophilic addition than alkylcyanides

The dialkylcyanamide complexes Q[PtCl3(NCNR2)] (Q = Ph3PCH2Ph, R2 = Me21, Et22, C5H103, C4H8O 4; Q = NMe4, R2 = Me25; Q = NEt4, R2 = Me26) were synthesized either by dissolving Q2[Pt2(μ-Cl)2Cl4] in neat NCNR2 (1-4) or by substitution of a NCNR2 ligand with Cl(-) in [PtCl2(NCNR2)2] by its treatment with QCl (5, 6). Nucleophilic addition of dibenzylhydroxylamine, HON(CH2Ph)2, to 1-6 results in the formation of the complexes Q[PtCl3{NHC(NR2)ON(CH2Ph)2}] (Q = Ph3PCH2Ph, R2 = Me2, 7; Et2, 8; C5H10, 9; C4H8O, 10; Q = Me4N, R2 = Me211; Q = Et4N, R2 = Me2, 12) that further convert at room temperature in the solid state (1-24 h) or in a solution (0.5-2 h) to the imine complexes Q[PtCl3{N(CH2Ph)=C(H)Ph}] (Q = Ph3PCH2Ph, 13; Me4N, 14; Et4N, 15) and the corresponding dialkylureas H2NC(=O)NR2. The competitive reactivity study of the nucleophilic addition of HON(CH2Ph)2 to (Ph3PCH2Ph)[PtCl3(NCR')] (R' = Ph, NR2, CH2Ph) indicated that the reactivity of the coordinated NCNR2 is comparable to NCPh, while NCCH2Ph appeared to be much less reactive than the former two ligands. Compounds 1-6 and 13 were fully characterized by elemental analyses (C, H, N), high resolution ESI-MS, IR, and (1)H and (13)C{(1)H} NMR spectroscopy. The structure of 1 was additionally verified by a single-crystal X-ray diffraction.

Novel imino thioether complexes of platinum(II): synthesis, structural investigation, and biological activity

The reactions of the nitrile complexes cis- and trans-[PtCl2(NCR)2] (R = Me, Et, CH2Ph, Ph) with an excess of ethanethiol, EtSH, in the presence of a catalytic amount of n-BuLi in tetrahydrofuran (THF), afforded in good yield the bis-imino thioether derivatives cis-[PtCl2{E-N(H)═C(SEt)R}2] (R = Me (1), Et (2), CH2Ph (3), Ph (4)) and trans-[PtCl2{E-N(H)═C(SEt)R}2] (R = Me (5), Et (6), CH2Ph (7), Ph (8)). The imino thioether ligands assumed the E configuration corresponding to a cis addition of the thiol to the nitrile triple bond. The spectroscopic properties of these complexes have been reported along with the molecular structures of 1, 2, and 7 as established by X-ray crystallography which indicated that these compounds exhibit square-planar coordination geometry around the platinum center. Four N-H···Cl intermolecular contacts (N-H···Cl ca. 2.5-2.7 Å) between each chlorine atom and the N-H proton of the imino thioether ligand gave rise to "dimers" Pt2Cl4L4 (L = imino thioether) formed by two PtCl2L2 units. The cytotoxic properties of these new platinum(II) complexes were evaluated against various human cancer cell lines. Among all derivatives, trans-[PtCl2{E-N(H)═C(SEt)CH2Ph}2] showed the greatest in vitro cytotoxic activity being able to decrease cancer cell viability roughly 3-fold more effectively than cisplatin.