An Efficient Conjugation Approach for Coupling Drugs to Native Antibodies via the PtII Linker Lx for Improved Manufacturability of Antibody-Drug Conjugates.

The PtII linker [ethylenediamineplatinum(II)]2+ , coined Lx, has emerged as a novel non-conventional approach to antibody-drug conjugates (ADCs) and has shown its potential in preclinical in vitro and in vivo benchmark studies. A crucial improvement of the Lx conjugation reaction from initially <15 % to ca. 75-90 % conjugation efficiency is described, resulting from a systematic screening of all relevant reaction parameters. NaI, a strikingly simple inorganic salt additive, greatly improves the conjugation efficiency as well as the conjugation selectivity simply by exchanging the leaving chloride ligand on Cl-Lx-drug complexes (which are direct precursors for Lx-ADCs) for iodide, thus generating I-Lx-drug complexes as more reactive species. Using this iodide effect, we developed a general and highly practical conjugation procedure that is scalable: our lead Lx-ADC was produced on a 5 g scale with an outstanding conjugation efficiency of 89 %.

Tuning the cytotoxic properties of new ruthenium(III) and ruthenium(II) complexes with a modified bis(arylimino)pyridine Schiff base ligand using bidentate pyridine-based ligands.

Synthesis, spectroscopy, characterization, structures, and cytotoxicity studies of 2,6-bis(2,6-diisopropylphenyliminomethyl)pyridine (LLL) ruthenium compounds are described. The starting compound [RuCl3(LLL)] has been fully characterized using IR spectroscopy, UV-vis spectroscopy, electrospray ionization mass spectrometry, and NMR spectroscopy. In addition, the crystal structure of the ligand LLL has been determined using single-crystal X-ray diffraction. With the ruthenium(III) trichloride compound as starting material, a new family of Ru(II) complexes with a number of neutral and charged bidentate co-ligands have been synthesized and used for characterization and cytotoxicity studies. The synthesis of the corresponding [Ru(II)LLL(LL)Cl](+/0) complexes with co-ligands- LL is 1,10-phenanthroline, 2,2'-bipyridyl, 2-(phenylazo)pyridine, 2-(phenylazo)-3-methylpyridine, 2-(tolylazo)pyridine, or the anionic 2-picolinate-is reported. Analytical, spectroscopic (IR spectroscopy, UV-vis spectroscopy, (1)H NMR spectroscopy, and electrospray ionization mass spectrometry), and structural characterization of the new compounds is described. Crystal structure analyses of two Ru(II) compounds show a slightly distorted octahedral Ru(II) geometry with tridentate LLL coordinated in a planar meridional fashion, and the chelating co-ligand (LL) and a chloride ion complete the octahedron. The co-ligand plays a significant role in modulating the physicochemical and cytotoxic properties of these new ruthenium complexes. The in vitro cytotoxicity of these new Ru(II) complexes (half-maximal inhibitory concentration, IC50, of 0.5-1.5 µM), in comparison with the parent Ru(III) compound (half-maximal inhibitory concentration of 3.9-4.3 µM) is higher for several of the human cancer cell lines tested. The cytotoxic activity of some of the new ruthenium compounds is even higher than that of cisplatin in the same cancer cell lines. The cytotoxicity of these new anticancer compounds is discussed in the light of structure-based activity relationships, and a possible mechanism of action is suggested.

Coordination chemistry beyond Werner: interplay between hydrogen bonding and coordination.

A tutorial review is presented dealing with the role of hydrogen bonding in coordination compounds. Examples are given for important intramolecular hydrogen bonding, and stabilising unusual coordination geometries, or reactive species. Also examples are discussed for intermolecular H-bonds between coordination entities and anions, and for stabilising crystal lattices, like in coordination polymers.

Bis{µ-2-[(4,6-bis{(2-hydroxy-5-methylphenyl)[(pyridin-2-yl)methyl]amino}-1,3,5-triazin-2-yl)[(pyridin-2-yl-κN)methyl]amino-κN]-4-methyl-phenolato-1:2κO:O}bis-[(nitrato-κO,O')zinc]-acetonitrile-water (2/4/1).

The title compound, [Zn(2)(C(42)H(38)N(9)O(3))(2)(NO(3))(2)]·2CH(3)CN·0.5H(2)O, is a bis-phenolate-bridged dinuclear Zn(II) complex. The asymmetric unit comprises half the zinc complex (the full complex is completed by the application of a centre of inversion), one acetonitrile solvent mol-ecule and a quarter of a water mol-ecule (located on a twofold axis with half-occupancy; H atoms were not located for this mol-ecule). Each triazine-based multidentate ligand uses a phenolate group to bridge Zn(II) ions, generating a Zn(2)O(2) core. The Zn(II) ions are five-coordinate, with an additional long Zn-O contact [2.6465 (16) Å], and include a semi-bidentate nitrate ion and a N,N',O-tridentate mode of the ligand in the coordination sphere. Non-coordinating pyridine groups form intra-molecular O-H⋯N hydrogen bonds with phenol groups. As suggested by the short O⋯O donor-acceptor distances between the disordered water molecules and phenol O atoms, these groups also participate in hydrogen bonding.

2-Chloro-pyrimidin-4-amine.

In the title pyrimidine derivative, C(4)H(4)ClN(3), the 2-chloro and 4-amino substituents almost lie in the mean plane of the pyrimidine ring, with deviations of 0.003 (1) Šfor the Cl atom, and 0.020 (1) Šfor the N atom. In the crystal, molecules are linked via pairs of N-H⋯N hydrogen bonds, forming inversion dimers. These dimers are further linked via N-H⋯N hydrogen bonds, forming an undulating two-dimensional network lying parallel to (100).

Tetra-hedral zinc in tetra-kis-(1-methyl-1H-imidazole-κN)zinc bis-(tetra-fluorido-borate).

In the title compound, [Zn(C(4)H(6)N(2))(4)](BF(4))(2), the Zn(II) ion is in a slightly distorted tetra-hedral coordination geometry, with Zn-N distances in the range 1.980 (2)-1.991 (2) Å. The tetra-hedral angles are in the range 104.93 (9)-118.81 (9)°.

Concomitant dimorphism in poly[di-µ-azido-(5,5'-dimethyl-2,2'-bipyridine)iron(II)].

The title metal-organic polymer, catena-poly[[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-µ-azido-κ2N1:N3-[(5,5'-dimethyl-2,2'-bipyridine-κ2N,N')iron(II)]-di-µ-azido-κ2N1:N1], [Fe(N3)2(C12H12N2)]n, features alternating µ-1,1 (end-on mode of coordination) and µ-1,3 (end-to-end mode of coordination) double azide bridges, forming chains running in the [100] direction. The octahedral coordination geometry around the FeII centre is completed by a bidentate 5,5'-dimethyl-2,2'-bipyridine ligand. Two polymorphs for this compound were obtained from the crude reaction product, the first in the space group P-1 and the other in P21/c. The molecular and crystal structures are very similar for both forms, the main difference being that the eight-membered Fe(µ-1,3-N3)2Fe metallacycle formed with end-to-end azide ligands has a nearly flat conformation in the triclinic form and a chair conformation in the monoclinic form. In spite of this geometric difference, both forms have the same density, the same packing index and similar arrangements of the one-dimensional chains in the crystal. As a consequence, they also share very similar Hirshfeld surfaces and fingerprint plots. However, a density functional theory (DFT) computational study showed that the monoclinic form is more stable than the triclinic form by ca 30.5 kJ mol-1.

A rare example of a double metamagnetic transition leading to 2D and 3D long-range order in the two-dimensional pyrazine- and azido-bridged cobalt(II) compound [Co(pyz)(N3)2].

The synthesis, characterization, crystal structure and detailed magnetic properties of a pyrazine (pyz) and azido (N3) bridged cobalt(II) compound of formula [Co(N3)2(pyz)] (1) are reported. Compound 1 shows a layered structure formed by Co(II) chains with double µ-N3(κN1,N1) bridges that are further connected by µ-(pyrazine-κN1,N4) bridges. The layers present weak van der Waals interactions between azido terminal groups. The magnetic properties show the presence of a metamagnetic behaviour in 1 with two critical fields of 200 and 400 mT at low temperatures. AC magnetic measurements show the presence of a long-range 2D ferromagnetic order at Tc ≈ 8.0-7.0 K for dc fields above 200 mT and a long-range 3D ferromagnetic order at Tc ≈ 4.5 K for dc fields above 400 mT.

Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies.

The newly synthesized dinuclear complex [Fe(III)(2)(µ-OH)(2)(bik)(4)](NO(3))(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe···Fe (3.0723(6) Å) and Fe-O distances (1.941(2)/1.949(2) Å) compared to other unsupported Fe(III)(2)(µ-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The (57)Fe isomer shift (δ = 0.45 mm s(-1)) and quadrupole splitting (ΔE(Q) = 0.26 mm s(-1)) obtained from Mössbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1)·S(2)) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe···Fe and Fe-OH distances are overestimated (3.281 and 2.034 Å, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 Å) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe(II)(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe(II)(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe(II)(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3°/2° value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O(2), and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.

Putting anion-π interactions into perspective.

Supramolecular chemistry is a field of scientific exploration that probes the relationship between molecular structure and function. It is the chemistry of the noncovalent bond, which forms the basis of highly specific recognition, transport, and regulation events that actuate biological processes. The classic design principles of supramolecular chemistry include strong, directional interactions like hydrogen bonding, halogen bonding, and cation-π complexation, as well as less directional forces like ion pairing, π-π, solvophobic, and van der Waals potentials. In recent years, the anion-π interaction (an attractive force between an electron-deficient aromatic π system and an anion) has been recognized as a hitherto unexplored noncovalent bond, the nature of which has been interpreted through both experimental and theoretical investigations. The design of selective anion receptors and channels based on this interaction represent important advances in the field of supramolecular chemistry. The objectives of this Review are 1) to discuss current thinking on the nature of this interaction, 2) to survey key experimental work in which anion-π bonding is demonstrated, and 3) to provide insights into the directional nature of anion-π contact in X-ray crystal structures.

Accurate non-invasive image-based cytotoxicity assays for cultured cells.

BACKGROUND: The CloneSelect Imager system is an image-based visualisation system for cell growth assessment. Traditionally cell proliferation is measured with the colorimetric MTT assay. RESULTS: Here we show that both the CloneSelect Imager and the MTT approach result in comparable EC50 values when assaying the cytotoxicity of cisplatin and oxaliplatin on various cell lines. However, the image-based technique was found non-invasive, considerably quicker and more accurate than the MTT assay. CONCLUSIONS: This new image-based technique has the potential to replace the cumbersome MTT assay when fast, unbiased and high-throughput cytotoxicity assays are requested.

Unprecedented water addition to the α,ß-unsaturated enone bond, mediated by the combination of carbonate and platinum(II).

The cytostatic compounds cis-[Pt(A9pyp)(dmso)Cl(2)] (1) and [Pt(A9pyp)(dmso)(cbdca)] (2) (A9pyp=(E)-[1-(9-anthryl)-3-(2-pyridyl)-2-propenone) as carrier ligand; cbdca=cyclobutane dicarboxylate) have been found to add water across the enone C==C bond of the ligand A9pyp. The water addition occurs in the presence of carbonate buffer, and has been followed in detail using NMR and ESI-MS spectroscopy. The spectroscopic data clearly indicate that the platinum(II) ion, the carbonate species, and the proximity of the enone C==C bond to the metal ion, are all required for this unusual hydration. A difference in kinetics is observed between chloride and cbdca, showing that the Pt-ligand dissociation plays an important role in the hydration kinetics.

Magnetothermal studies of a series of coordination clusters built from ferromagnetically coupled {Mn(II) (4)Mn(III) (6)} supertetrahedral units.

Three high-nuclearity mixed valence manganese(II/III) coordination clusters, have been synthesised, that is, [Mn(III) (6)Mn(II) (4)(µ(3)-O)(4)(HL(1))(6)(µ(3)-N(3))(3)(µ(3)-Br)(Br)](N(3))(0.7)/(Br)(0.3)⋅3 MeCN⋅2 MeOH (1) (H(3)L(1)=3-methylpentan-1,3,5-triol), [Mn(III) (11)Mn(II) (6)(µ(4)-O)(8)(µ(3)-Cl)(4)(µ,µ(3)-O(2)CMe)(2)(µ,µ-L(2))(10)Cl(2.34)(O(2)CMe)(0.66)(py)(3)(MeCN)(2)]⋅7 MeCN (2) (H(2)L(2)=2,2-dimethyl-1,3-propanediol and py is pyridine), and [Mn(III) (12)Mn(II) (7)(µ(4)-O)(8)(µ(3)-η(1)N(3))(8)(HL(3))(12)(MeCN)(6)]Cl(2)⋅10 MeOH ⋅MeCN (3) (H(3)L(3)=2,6-bis(hydroxymethyl)-4-methylphenol) with high ground-spin states, S=22, 28±1, and 83/2, respectively; their magnetothermal properties have been studied. The three compounds are based on a common supertetrahedral building block as seen in the Mn(10) cluster. This fundamental magnetic unit is made up of a tetrahedron of Mn(II) ions with six Mn(III) ions placed midway along each edge giving an inscribed octahedron. Thus, the fundamental building unit as represented by compound 1 can be described as a Mn(10) supertetrahedron. Compounds 2 and 3 correspond to two such units joined by a common edge or vertex, respectively, resulting in Mn(17) and Mn(19) coordination clusters. Magnetothermal studies reveal that all three compounds show interesting long-range magnetic ordering at low temperature, originating from negligible magnetic anisotropy of the compounds; compound 2 shows the largest magnetocaloric effect among the three compounds. This is as expected and can be attributed to the presence of a small magnetic anisotropy, and low-lying excited states in compound 2.

An S-shaped [Fe(4)Dy(2)] complex exhibiting slow relaxation of magnetization: synthesis, magnetism, and crystal structures of a family of [Fe(4)Ln(2)][Ln] coordination compounds (Ln = Nd, Gd, Tb, Dy, and Ho).

A series of heterobimetallic 3d-4f cluster coordination compounds has been synthesized using a Schiff-base ligand (H(3)L), a trinuclear iron(III) precursor complex and lanthanide nitrates as reactants. Five new isostructural complexes were prepared with the ligand in 4 different forms, i.e., neutral and 3 different levels of deprotonation, and with the general formula [Fe(III)(4)Ln(III)(2)(H(2)L)(2)(HL)(2)L(2)(CH(3)OH)(2)((CH(3))(3)CCOO)(2)(NO(3))(2)][Ln(III)(NO(3))(4)(H(3)L)(CH(3)OH)].NO(3).H(2)O, where Ln is Nd, Gd, Tb, Dy, and Ho for compounds 1, 2, 3, 4, and 5, respectively. The single-crystal structures of two complexes were determined by X-ray diffraction, consisting of an original [Fe(III)(4)Ln(III)(2)](2+) moiety with a linear S-shaped [Ln-Fe(4)-Ln] core and an isolated Ln(III) ion coordinated by nitrate anions and the neutral Schiff-base ligand. The isostructural nature of all five coordination compounds is further illustrated both by XRPD and IR analysis. Magnetic properties of all five compounds have been studied and are discussed in light of magnetostructural considerations. Among these five compounds, the Dy (4) cluster shows frequency-dependent ac-susceptibility indicative of probable single-molecule magnet behavior.

Reliability and storage capacity: a compromise illustrated in the two-step spin-crossover system [Fe(bapbpy)(NCS)(2)].

The design of bistable magnetic systems should enable the storage of information by manipulation of the spin degrees of freedom. However, such a strategy relies on the preparation of target objects, whose environment must be controlled to favor a hysteretic behavior. Here, we report the successful modeling of a highly cooperative two-step spin-crossover iron(II) compound, [Fe(bapbpy)(NCS)(2)]. The magnetic susceptibility measurements and low- and high-temperature hysteretic cycles reflect the presence of an intermediate phase, which controls the memory-storage capacity of this material. It is shown that the hysteresis loop widths can be traced theoretically by evaluating the electrostatic contributions between the transiting units. Despite the apparent reduction of intermolecular interactions upon cooling, it is suggested that the enhanced fluctuations of the Madelung field are responsible for the observed hysteresis width changes. This counterintuitive scenario makes the preparation of information storage devices an even more challenging task, where theoretical inspections are very insightful.

Discrete tetrairon(III) cluster exhibiting a square-planar Fe4(mu4-O) core: structural and magnetic properties.

The aerobic reaction of the Schiff-base ligand N-(benzimidazol-2-yl)salicylaldimine (Hbisi) with iron(II) perchlorate in methanol leads to the formation of the remarkable coordination compound [Fe(4)(mu(4)-O)(mu-MeO)(4)(bisi)(4)](ClO(4))(2) x 4 MeOH (1), whose single-crystal X-ray structure reveals the presence of a discrete Fe(III)(4)(mu(4)-O) core. Magnetic and Mossbauer studies both show that the exchange interaction within the square tetranuclear iron(III) unit is dominated by the central bridging mu(4)-oxido ligand, the involvement of the mu-methoxido bridges being negligible.

Copper curcuminoids containing anthracene groups: fluorescent molecules with cytotoxic activity.

The coordination chemistry of the new curcuminoid ligand, 1,7-(di-9-anthracene-1,6-heptadiene-3,5-dione), abbreviated 9Accm has been studied, resulting in two new copper-9Accm compounds. Compound 1, [Cu(phen)Cl(9Accm)], was synthesized by reacting 9Accm with [Cu(phen)Cl(2)] in a 1:1 ratio (M:L) and compound 2, [Cu(9Accm)(2)], was prepared from Cu(OAc)(2) and 9Accm (1:2). UV-vis, electron paramagnetic resonance (EPR), and superconducting quantum interference device (SQUID) measurements were some of the techniques employed to portray these species; studies on single crystals of free 9Accm, [Cu(phen)Cl(9Accm)] and [Cu(9Accm)(2)(py)] provided detailed structural information about compounds 1 and 2·py, being the first two copper-curcuminoids crystallographically described. In addition the antitumor activity of the new compounds was studied and compared with free 9Accm for a number of human tumor cells. To provide more insight on the mode of action of these compounds under biological conditions, additional experiments were accomplished, including studies on the nature of their interactions with calf thymus DNA by UV-vis titration and Circular Dichroism. These experiments together with DNA-binding studies indicate electrostatic interactions between some of these species and the double helix, pointing out the weak nature of the interaction of the compounds with CT-DNA. The intrinsic fluorescence of the free ligand and both copper compounds provided valuable information over the cellular process and therefore, fluorescence microscopy studies were performed using a human osteosarcoma cell line. Studies in vitro using this technique suggest that the action of these molecules seems to occur outside the nuclei.

High cytotoxicity of cisplatin nanocapsules in ovarian carcinoma cells depends on uptake by caveolae-mediated endocytosis.

PURPOSE: Cisplatin nanocapsules, nanoprecipitates of cisplatin encapsulated in phospholipid bilayers, exhibit increased in vitro toxicity compared with the free drug toward a panel of human ovarian carcinoma cell lines. To elucidate the mechanism of cell killing by nanocapsules and to understand the cell line dependence of nanocapsule efficacy, the route of uptake and the intracellular fate of the nanocapsules were investigated. EXPERIMENTAL DESIGN: Intracellular platinum accumulation and cisplatin-DNA-adduct formation were measured in cell lines that differ in sensitivity to cisplatin nanocapsules. Confocal fluorescence microscopy in combination with down-regulation with small interfering RNA was used to map the route of cellular uptake of nanocapsules containing fluorescein-labeled cisplatin. RESULTS: In sensitive cell lines, cisplatin from nanocapsules is taken up much more efficiently than the free compound. In IGROV-1 cells, the increased platinum accumulation results in augmented cisplatin-DNA-adduct formation. Confocal fluorescence microscopy revealed that the uptake of nanocapsules is energy dependent. Colocalization with markers of early and late endosomes indicated uptake via endocytosis. Down-regulation of caveolin-1 with small interfering RNA inhibited the uptake and cytotoxic effect of nanocapsules in IGROV-1 cells. Ovarian carcinoma cells, in which the nanocapsules are less effective than in IGROV-1 cells, do not internalize the nanocapsules (OVCAR-3) or accumulate them in an endocytic compartment after clathrin-mediated endocytosis (A2780). CONCLUSIONS: The high cytotoxicity of cisplatin nanocapsules requires caveolin-1-dependent endocytosis that is followed by release of the drug from a late endosomal/lysosomal compartment and cisplatin-DNA-adduct formation. The findings may be applied in predicting the efficacy of nanoparticulate anticancer drug delivery systems in treating different tumor types.

Fifty years of inorganic biochemistry: Developments, trends, highlights, impact and citations.

A brief historic overview and analysis is presented of the almost 9000 scientific articles that have appeared in the Journal of Inorganic Biochemistry (JIB) and its predecessor (Bioinorganic Chemistry), since 1973. This overview has a focus on the different topics, in particular on the different elements of the Periodic Table and on papers that have received very large numbers of citations. Over the whole period, copper has been the element occurring in most publications (almost 1800, which is 20%), followed by iron which occurs in some 12% of all papers. Other favorite elements are zinc, platinum and ruthenium. The worldwide origin of papers published in JIB has been analyzed as well, showing a quite evenly worldwide distribution, with just a few exceptions. Trends in selected scientific topics over time (first 10 years; last 25 years, last 10 years) are also discussed. Also authors and institutes with the largest number of papers published in JIB have been detected. The numerical information is based on an analysis of the Web of Science with a cutoff date around July 1, 2020.

DNA and glutathione interactions in cell-free media of asymmetric platinum(II) complexes cis- and trans-[PtCl2(isopropylamine)(1-methylimidazole)]: relations to their different antitumor effects.

The global modification of mammalian and plasmid DNAs by the novel platinum compounds cis-[PtCl(2)(isopropylamine)(1-methylimidazole)] and trans-[PtCl(2)(isopropylamine)(1-methylimidazole)] and the reactivity of these compounds with reduced glutathione (GSH) were investigated in cell-free media using various biochemical and biophysical methods. Earlier cytotoxicity studies had revealed that the replacement of the NH(3) groups in cisplatin by the azole and isopropylamine ligands lowers the activity of cisplatin in both sensitive and resistant cell lines. The results of the present work show that this replacement does not considerably affect the DNA modifications by this drug, recognition of these modifications by HMGB1 protein, their repair, and reactivity of the platinum complex with GSH. These results were interpreted to mean that the reduced activity of this analog of cisplatin in tumor cell lines is due to factors that do not operate at the level of the target DNA. In contrast, earlier studies had shown that the replacement of the NH(3) groups in the clinically ineffective trans isomer (transplatin) by the azole and isopropylamine ligands results in a radical enhancement of its activity in tumor cell lines. Importantly, this replacement also markedly alters the DNA binding mode of transplatin, which is distinctly different from that of cisplatin, but does not affect reactivity with GSH. Hence, the results of the present work are consistent with the view and support the hypothesis systematically tested by us and others that platinum drugs that bind to DNA in a fundamentally different manner from that of conventional cisplatin may have altered pharmacological properties.