The relationship between electrospray ionization behavior and cytotoxic activity of [M(I)(P)4](+)-type complexes (M = Cu, Ag and Au; P = tertiary phosphine)

Synthesis of a Novel Series of Cu(I) Complexes Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Homogeneous and Carbon-Supported Catalysts for the Synthesis of 1- and 2-Substituted-1,2,3-triazoles

The N-alkylation of 1,3,5-triaza-7-phosphaadamantane (PTA) with ortho-, meta- and para-substituted nitrobenzyl bromide under mild conditions afforded three hydrophilic PTA ammonium salts, which were used to obtain a new set of seven water-soluble copper(I) complexes. The new compounds were fully characterized and their catalytic activity was investigated for the low power microwave assisted one-pot azide-alkyne cycloaddition reaction in homogeneous aqueous medium to obtain disubstituted 1,2,3-triazoles. The most active catalysts were immobilized on activated carbon (AC), multi-walled carbon nanotubes (CNT), as well as surface functionalized AC and CNT, with the most efficient support being the CNT treated with nitric acid and NaOH. In the presence of the immobilized catalyst, several 1,4-disubstituted-1,2,3-triazoles were obtained from the reaction of terminal alkynes, organic halides and sodium azide in moderate yields up to 80%. Furthermore, the catalyzed reaction of terminal alkynes, formaldehyde and sodium azide afforded 2-hydroxymethyl-2H-1,2,3-triazoles in high yields up to 99%. The immobilized catalyst can be recovered and recycled through simple workup steps and reused up to five consecutive cycles without a marked loss in activity. The described catalytic systems proceed with a broad substrate scope, under microwave irradiation in aqueous medium and according to "click rules".

A new amido-phosphane as ligand for copper and silver complexes. Synthesis, characterization and catalytic application for azide-alkyne cycloaddition in glycerol

The new sterically hindered amido-phosphane 1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane-3,7-diylbis(phenylmethanone), DBPTA (1), has been obtained via an open-cage double N-acylation of 1,3,5-triaza-7-phosphadamantane (PTA) using benzoic anhydride. DBPTA is the only acyl derivative of PTA that contains an aromatic appendage. Due to the bulky nature of the benzoyl C(O)Ph groups, they exhibit mutual anti configuration as confirmed by solution NMR and single crystal X-ray diffraction. Compound 1 is readily soluble in common polar organic and green solvents, making it a very versatile ligand that could be used in a variety of reaction systems. To assess the coordination characteristics of the new phosphane, seven copper complexes of formulas [Cu(DBPTA)4]BF4 (2), [CuX(DBPTA)3] {X = Br (3) and I (4)}, [Cu(μ-X)(DBPTA)2]2 {X = Br (5) and I (6)}, [Cu(bpy)(DBPTA)2]Y {Y = BF4 (7) and BPh4 (8)} {bpy = 2,2'-bipyridine}, and three silver complexes with formulas [Ag(DBPTA)4]NO3 (9), [Ag(Tpm*)(DBPTA)]NO3 (10) and [Ag(Tpms)(DBPTA)] (11) {Tpm* = tris(3,5-dimethyl-1-pyrazolyl)methane, Tpms = tris(pyrazol-1-yl)methanesulfonate} have been synthesised. Compounds 1-11 were characterized by elemental analyses and electrospray ionization mass spectrometry (ESI-MS), as well as by FT-IR and NMR (1H, 13C, 31P, COSY and HSQC) spectroscopic techniques. The catalytic activity of the complexes has been investigated for 1,3-dipolar azide-alkyne cycloaddition reaction using glycerol as a reaction medium to afford 1,4-disubstituted-1,2,3-triazoles. Complex 7 was found to be the most efficient catalyst, affording triazoles in yields up to 97% after 18 h under standard bench experimental conditions (at 23 °C, aerobic conditions and in the absence of any additional bases) and up to 98% after 15 minutes under microwave irradiation (125 °C, 30 W). The catalysis proceeds with a broad substrate scope according to "Click" rules providing a significant contribution to "Green Chemistry".

Antiproliferative Homoleptic and Heteroleptic Phosphino Silver(I) Complexes: Effect of Ligand Combination on Their Biological Mechanism of Action

A series of neutral mixed-ligand [HB(pz)₃]Ag(PR₃) silver(I) complexes (PR₃ = tertiary phosphine, [HB(pz)₃]⁻ = tris(pyrazolyl)borate anion), and the corresponding homoleptic [Ag(PR₃)₄]BF₄ compounds have been synthesized and fully characterized. Silver compounds were screened for their antiproliferative activities against a wide panel of human cancer cells derived from solid tumors and endowed with different platinum drug sensitivity. Mixed-ligand complexes were generally more effective than the corresponding homoleptic derivatives, but the most active compounds were [HB(pz)₃]Ag(PPh₃) (5) and [Ag(PPh₃)₄]BF₄ (10), both comprising the lipophilic PPh₃ phosphine ligand. Detailed mechanistic studies revealed that both homoleptic and heteroleptic silver complexes strongly and selectively inhibit the selenoenzyme thioredoxin reductase both as isolated enzyme and in human ovarian cancer cells (half inhibition concentration values in the nanomolar range) causing the disruption of cellular thiol-redox homeostasis, and leading to apoptotic cell death. Moreover, for heteroleptic Ag(I) derivatives, an additional ability to damage nuclear DNA has been detected. These results confirm the importance of the type of silver ion coordinating ligands in affecting the biological behavior of the overall corresponding silver complexes, besides in terms of hydrophilic–lipophilic balance, also in terms of biological mechanism of action, such as interaction with DNA and/or thioredoxin reductase.

Cu(i) and Ag(i) complex formation with the hydrophilic phosphine 1,3,5-triaza-7-phosphadamantane in different ionic media. How to estimate the effect of a complexing medium

The complexes of Cu(i) and Ag(i) with 1,3,5-triaza-7-phosphadamantane (PTA) are currently studied for their potential clinical use as anticancer agents, given the cytotoxicity they exhibited in vitro towards a panel of several human tumor cell lines. These metallodrugs are prepared in the form of [M(PTA)₄]⁺ (M = Cu⁺, Ag⁺) compounds and dissolved in physiological solution for their administration. However, the nature of the species involved in the cytotoxic activity of the compounds is often unknown. In the present work, the thermodynamics of formation of the complexes of Cu(i) and Ag(i) with PTA in aqueous solution is investigated by means of potentiometric, spectrophotometric and microcalorimetric methods. The results show that both metal(i) ions form up to four successive complexes with PTA. The formation of Ag(i) complexes is studied at 298.15 K in 0.1 M NaNO₃ whereas the formation of the Cu(i) one is studied in 1 M NaCl, where Cu(i) is stabilized by the formation of three successive chloro-complexes. Therefore, for this latter system, conditional stability constants and thermodynamic data are obtained. To estimate the affinity of Cu(i) for PTA in the absence of chloride, Density Functional Theory (DFT) calculations have been done to obtain the stoichiometry and the relative stability of the possible Cu/PTA/Cl species. Results indicate that one chloride ion is involved in the formation of the first two complexes of Cu(i) ([CuCl(PTA)] and [CuCl(PTA)₂]) whereas it is absent in the successive ones ([Cu(PTA)₃]⁺ and [Cu(PTA)₄]⁺). The combination of DFT results and thermodynamic experimental data has been used to estimate the stability constants of the four [Cu(PTA)_n]⁺ (n = 1-4) complexes in an ideal non-complexing medium. The calculated stability constants are higher than the corresponding conditional values and show that PTA prefers Cu(i) to the Ag(i) ion. The approach used here to estimate the hidden role of chloride on the conditional stability constants of Cu(i) complexes may be applied to any Cu(i)/ligand system, provided that the stoichiometry of the species in NaCl solution is known. The speciation for the two systems shows that the [M(PTA)₄]⁺ (M = Cu⁺, Ag⁺) complexes present in the metallodrugs are dissociated into lower stoichiometry species when diluted to the micromolar concentration range, typical of the in vitro biological testing. Accordingly, [Cu(PTA)₂]⁺, [Cu(PTA)₃]⁺ and [Ag(PTA)₂]⁺ are predicted to be the species actually involved in the cytotoxic activity of these compounds.

Interaction products of cytotoxic Cu(I) complexes with different solvent mixtures: an electrospray ionization mass spectrometry and density functional theory study

RATIONALE

[Cu(P)₄ ][BF₄ ]-type complexes (P = tertiary phosphine) have shown significant antitumor activity. This biological property appears to be activated via formation of coordinative unsaturated [Cu(P)_n ]⁺ species (n < 4), that may interact with various molecules starting from the solvent(s) in which they are dissolved. Aim of our study was to investigate the interaction of these species with different solvent mixtures.

METHODS

The interaction has been investigated by electrospray ionization mass spectrometry, and the interaction products have been characterized by multiple collisional experiments, using an ion trap mass instrument. Density functional theory (DFT) calculation studies, using a meta-hybrid exchange correlation (xc) functional and an implicit solvent model, were employed to investigate the equilibrium distribution of species in solution.

RESULTS

Depending on the nature of the solvent mixture and coordinated phosphine, three [Cu(P)₄ ][BF₄ ]-type complexes undergo dissociation with formation of [Cu(P)₂ ]⁺ , [Cu(P)(solv)]⁺ and [Cu(solv)₂ ]⁺ species (solv = solvent). Preferred collisional-induced fragmentation pathways provide qualitative information on the selectivity of [Cu(P)_n ]⁺ for specific solvents and donor atoms. Formation free energies and equilibrium constants pertaining to [Cu^I (PTA)_n ]⁺ , [Cu^I/II (solv)_n ]^m+ (n ≤ 4; m = 1, 2) and [Cu^I (PTA)_2-k (sol)_k ]⁺ (k = 1, 2) provide a comprehensive picture of equilibria in solution.

CONCLUSIONS

Dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) strongly affect [Cu(P)_n ]⁺ assemblies producing mixed-ligand [Cu(P)(DMSO)]⁺ and [Cu(P)(MeCN)]⁺ species. Excess of both DMSO and MeCN solvents are able to fully displace coordinated phosphines giving [Cu(solv)₂ ]⁺ -type adducts. The presence of phosphines in the native complex is mandatory to retain the reduced oxidation state of copper. Instead, the more labile [Cu^I (MeCN)₄ ]⁺ complex dissolved in DMSO and MeCN displays a combination of Cu(I) and Cu(II) adducts. Copyright © 2016 John Wiley & Sons, Ltd.

Novel metalloantimalarials: Transmission blocking effects of water soluble Cu(I), Ag(I) and Au(I) phosphane complexes on the murine malaria parasite Plasmodium berghei

The water soluble phosphane complexes [M(L)₄]PF₆ (M=Cu(I), Ag(I)) and [Au(L)₄]Cl (L=thp (tris(hydroxymethyl)phosphane) or PTA (1,3,5-triaza-7-phosphaadamantane)) showed notable in vitro activity against Plasmodium early sporogonic stages, the sexual forms of the malaria parasite that are responsible for infection of the mosquito vector. Effects varied according to both, the type of metal and phosphane ligands. [Ag(thp)₄]PF₆ was the best performing complex exhibiting a half inhibitory concentration (IC₅₀) value in the low micromolar range (0.3-15.6μM). The silver complex [Ag(thp)₄]PF₆ was characterized by X-ray crystallography revealing that the structure comprises the cationic complex [Ag(thp)₄]⁺, the PF₆^- anion, and a water molecule of crystallization. Our results revealed that Cu(I), Ag(I) and Au(I) phosphanes complexes elicited similar activity profiles showing potential for the development of antimalarial, transmission blocking compounds. Molecules targeting the sexual parasite stages in the human and/or mosquito host are urgently needed to complement current artemisinin based treatments and next generation antimalarials in a vision not only to cure the disease but to interrupt its transmission.

Electrospray ionization in the study of the interactions between cytotoxic phosphino Cu(I) complexes and selected amino acids and GlyGlyHis peptide model

Tetrahedral [Cu(P)₄][BF₄]-type complexes (P = tertiary phosphine) are a class of monopositively charged compounds that have shown notable antitumor activity in both in vitro and in vivo tests. This biological property appears to be related to the peculiar physicochemical characteristics of these compounds. Although thermodynamically stable, they are labile at micromolar concentrations. Such a behavior allows the Cu(I) ion in [Cu(P)_n]⁺ assemblies (n < 4) to interact with surrounding molecules, including the rich peptide/protein environment that metal complexes have to face in the physiological milieu on the way to tumor cells. The scope of this investigation was to study the interaction products that originate from the treatment in water/methanol mixtures of representative phosphino Cu(I) compounds with an excess of individual amino acids (AAs) selected on the basis of the donor atom likely involved in metal coordination (i.e. O-glycine, S-methionine and N-histidine). These interactions have been investigated in electrospray ionization mass spectrometry (ESI-MS), mainly in the positive ion mode [ESI(+)MS], and the interaction products have been characterized by sequential collisional experiments, performed by an ion trap instrument. Histidine and methionine, but not glycine, were able to mine Cu(I) from [Cu(P)_n]⁺ assemblies through the formation of mixed [Cu^I(P)(AA)]⁺ and eventually [Cu^I(AA)₂]⁺ adducts. The ability to substitute phosphine(s) by AAs and the strongest affinity for Cu(I) was proved by the study of the energetics of collisional-induced decomposition (CID) reactions [Cu^I(P)(AA)]⁺ → Cu^I(AA) + P]⁺. Among the investigated AAs, histidine displayed the strongest affinity for Cu(I). Transchelation of Cu(I) was similarly observed when [Cu(P)_n]⁺ species were treated with the model tripeptide GlyGlyHis (GGH), the most investigated member of the amino terminal Cu(II) and Ni(II) (ATCUN) peptide family. GGH was able to form robust metal adducts not only with Cu(II) and the related divalent Zn(II) and Ni(II) ions, but also with monovalent ions, including Cu(I) and Ag(I). CID pathways of [Cu^I(GGH)]⁺ and [Ag^I(GGH)]⁺ were qualitatively superimposable and proceeded through losses of neutral fragments. Similar losses of neutral fragments were observed from [Zn^II(GGH)] and [Ni^II(GGH)]. CID pathways of [Cu^II(GGH)]^-/+ adducts instead took place mainly through intramolecular electron-transfer reactions comprising the reduction of Cu(II) to Cu(I) and the formation of fragment radical cations.

Homoleptic phosphino copper(I) complexes with in vitro and in vivo dual cytotoxic and anti-angiogenic activity

Homoleptic, tetrahedral Cu(i) complexes of the type [Cu(P)4]BF4 (1-3), where P are the phosphine ligands, 1,3,5-triaza-7-phosphaadamantane (PTA), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA) and 2-thia-1,3,5-triaza-phosphoaadamantane-2,2-dioxide (PTA-SO2), have been prepared. Novel complexes [Cu(DAPTA)4]BF42 and [Cu(PTA-SO2)4]BF43 have been fully characterized by means of spectroscopic methods, corroborated by XAS-EXAFS analysis of 2. In vitro cell culture experiments revealed a significant antiproliferative activity for Cu(i) compounds against several human cancer cell lines derived from solid tumors with preferential cell growth inhibition towards tumour compared to non-malignant cells. In vitro monitoring of migration and capillary-like tube formation of human umbilical vein endothelial cells (HUVECs) showed an anti-angiogenic effect of copper(i) complexes at sub-cytotoxic concentrations. In vivo studies on the antitumor efficacy and ability to inhibit angiogenesis confirmed the dual cytotoxic and anti-angiogenic properties of Cu(i) derivatives.