Hydrogen-Bonding Patterns in Oxime/Oximato Platinum(II) Species Providing the Formation of One-Dimensional Chains, Two-Dimensional Networks, and Cages

The Fundamental Role of Oxime and Oxime Ether Moieties in Improving the Physicochemical and Anticancer Properties of Structurally Diverse Scaffolds

The present review explores the critical role of oxime and oxime ether moieties in enhancing the physicochemical and anticancer properties of structurally diverse molecular frameworks. Specific examples are carefully selected to illustrate the distinct contributions of these functional groups to general strategies for molecular design, modulation of biological activities, computational modeling, and structure-activity relationship studies. An extensive literature search was conducted across three databases, including PubMed, Google Scholar, and Scifinder, enabling us to create one of the most comprehensive overviews of how oximes and oxime ethers impact antitumor activities within a wide range of structural frameworks. This search focused on various combinations of keywords or their synonyms, related to the anticancer activity of oximes and oxime ethers, structure-activity relationships, mechanism of action, as well as molecular dynamics and docking studies. Each article was evaluated based on its scientific merit and the depth of the study, resulting in 268 cited references and more than 336 illustrative chemical structures carefully selected to support this analysis. As many previous reviews focus on one subclass of this extensive family of compounds, this report represents one of the rare and fully comprehensive assessments of the anticancer potential of this group of molecules across diverse molecular scaffolds.

Ruthenium(II)-Dithiocarbazates as Anticancer Agents: Synthesis, Solution Behavior, and Mitochondria-Targeted Apoptotic Cell Death

The reaction of the Ru(PPh₃ )₃ Cl₂ with HL^1-3 -OH (-OH stands for the oxime hydroxyl group; HL¹ -OH=diacetylmonoxime-S-benzyldithiocarbazonate; HL² -OH=diacetylmonoxime-S-(4-methyl)benzyldithiocarbazonate; and HL³ -OH=diacetylmonoxime-S-(4-chloro)benzyl-dithiocarbazonate) gives three new ruthenium complexes [Ru^II (L^1-3 -H)(PPh₃ )₂ Cl] (1-3) (-H stands for imine hydrogen) coordinated with dithiocarbazate imine as the final products. All ruthenium(II) complexes (1-3) have been characterized by elemental (CHNS) analyses, IR, UV-vis, NMR (¹ H, ¹³ C, and ³¹ P) spectroscopy, HR-ESI-MS spectrometry and also, the structure of 1-2 was further confirmed by single crystal X-ray crystallography. The solution/aqueous stability, hydrophobicity, DNA interactions, and cell viability studies of 1-3 against HeLa, HT-29, and NIH-3T3 cell lines were performed. Cell viability results suggested 3 being the most cytotoxic of the series with IC₅₀ 6.9±0.2 μM against HeLa cells. Further, an apoptotic mechanism of cell death was confirmed by cell cycle analysis and Annexin V-FITC/PI double staining techniques. In this regard, the live cell confocal microscopy results revealed that compounds primarily target the mitochondria against HeLa, and HT-29 cell lines. Moreover, these ruthenium complexes elevate the ROS level by inducing mitochondria targeting apoptotic cell death.

A combined experimental and theoretical investigation of a new imineoxime and its palladium(II) and platinum(II) complexes: synthesis, structural characterization and spectroscopic properties

A new imineoxime compound {(1E,2E)-(2-hydroxy-ethylimino)-naphthalene-2yl-ethanal oxime (heineoH)} and its palladium(II) and platinum(II) complexes ([M(heineo)2]) have been synthesized and characterized by IR, NMR, UV-vis, elemental analysis, mass spectra and X-ray single crystal diffraction. [Pt(heineo)2] was obtained as a single crystal, while [Pd(heineo)2] was synthesized as a polycrystalline powder. The X-ray diffraction analysis of the [Pt(heineo)2] indicated that the platinum(II) ion is coordinated by two heineo ligands in a distorted square-planar geometry. DFT (B3LYP/6-311++G(d,p) and LANL2DZ) calculations on the ligand and its complexes were carried out to correlate the geometry and vibrational and electronic properties. Additionally, heineoH is fluorescent in EtOH at room temperature, but the fluorescence is quenched in the case of the metal complexes.

Use of the oxime–oximato binding mode to stabilise mixed valence copper iodide polymer networks using dipyridyl ketone oxime ligands

Coordination polymers formed from copper iodide and four isomeric dipyridyl ketone oxime ligands showed the importance the oxime–oximato bridge on the formation of mixed valence Cu(i)/Cu(ii) polymers.

A palladium(II) complex containing both carbonyl and imine oxime ligands: crystal structure, experimental and theoretical UV-vis, IR and NMR studies

A new palladium(II) complex, [Pd(ppeieo)(inap)]·DMSO (ppeieo=(1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime and inap=isonitrosoacetophenone) has been synthesized and characterized by elemental analysis, UV-vis, IR, NMR. X-ray diffraction analysis of the DMSO solvate of the complex shows that the palladium(II) ion is coordinated in a distorted square-planar geometry by ppeieo and inap, which is formed during the hydrolysis of ppeieo. DFT (B3LYP/LANL2DZ) calculations on the complex have been carried out to correlate geometry and spectroscopic properties such as electronic, vibrational and NMR chemical shifts. The complete vibrational frequency assignments were made and the calculation results were applied to simulate infrared spectra of the title compound which shows good agreement with observed spectra. The calculated HOMO and LUMO energies show that several transitions including the π→π(*) and charge transfer occur within the molecule. The chemical shifts reasonably correspond to the calculated spectra.

Synthesis, characterization, and cytotoxic activity of novel potentially pH-sensitive nonclassical platinum(II) complexes featuring 1,3-dihydroxyacetone oxime ligands

The reaction of 1,3-dihydroxyacetone oxime with diam(m)minediaquaplatinum(II) under basic conditions produced zwitterionic diam(m)mine(3-hydroxy-2-(oxidoimino)propan-1-olato-κ(2)N,O)platinum(II) complexes featuring the N,O-chelating ligand. Upon reaction with hydrochloric acid, it was possible to isolate either the singly protonated species still exhibiting the intact N,O-chelate or the open-chain chlorido complex. All complexes were characterized in detail with multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, ESI mass spectrometry, and in one case X-ray diffraction. Cytotoxicity was investigated in three human cancer cell lines (CH1, SW480, and A549). The obtained IC(50) values are in the medium or even low micromolar range, remarkable for platinum complexes having N(3)O or N(3)Cl coordination spheres. To study the solution behavior of the prepared complexes at physiologically relevant proton concentrations, time-dependent (1)H NMR measurements were performed for the ethane-1,2-diamine-containing series at pH values of 7.4, 6.0, and exemplarily 5.0. While the zwitterionic complex proved to be stable at both pH 7.4 and 6.0, the protonated species were deprotonated at pH 7.4, tending toward ring opening in slightly acidic environments, as characteristic for many solid tumors. Finally, the open-chain form stayed intact at pH 6.0, being completely converted into its chelated analogue at pH 7.4. A pH-dependent evaluation of antiproliferative effects of the two latter complexes at pH 7.4 and pH 6.0 revealed an activation under slightly acidic conditions, which might be of interest for further in vivo studies.

Novel cis- and trans-configured bis(oxime)platinum(II) complexes: synthesis, characterization, and cytotoxic activity

Novel cis- and trans-configured bis(oxime)platinum(II) complexes have been synthesized and characterized by elemental analyses, IR, electrospray ionization mass spectrometry, multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, and, in five cases, by X-ray diffraction. Their cytotoxicity was studied in the cisplatin-sensitive CH1 cell line as well as in inherently cisplatin-resistant SW480 cancer cells. Remarkably, every single dihalidobis(oxime)platinum(II) complex (with either a cis or trans configuration) shows a comparable cytotoxic potency in both cell lines, indicating a capacity of overcoming cisplatin resistance. Particularly strong cytotoxicities were observed in the case of trans-[PtCl(2)(R(2)C=NOH)(2)] (R = Me, n-Pr, i-Pr) with IC(50) values in the high nanomolar concentration range in both CH1 and SW480 cancer cells. These complexes are as potent as cisplatin in CH1 cells and up to 20 times more potent than cisplatin in SW480 cells. In comparison to transplatin, the novel compounds are up to 90 (CH1) and 120 times (SW480) more cytotoxic. The previously reported observation that the trans geometry yields a more active complex in the case of [PtCl(2)(Me(2)C=NOH)(2)] could be confirmed for at least two structural analogues.

Zinc(II)/ketoxime system as a simple and efficient catalyst for hydrolysis of organonitriles

The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH(2)Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC(6)H(4)CH(2), Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX(2)/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X(-) in the zinc salt (X = NO(3), Cl, CF(3)SO(3)) or of the ketoxime (Me(2)C=NOH, C(4)H(8)C=NOH, C(5)H(10)C=NOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO(3))(2).6H(2)O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC(6)H(4)CH(2)C(=O)NH(2). The previously unknown structures of the two carboxamide products n-BuC(=O)NH(2) and p-MeOC(6)H(4)CH(2)C(=O)NH(2) were determined by X-ray diffraction studies. The complexes [ZnX(2)(R(2)C=NOH)(2)] (X = Cl, R(2) = 2Me, C(4)H(8), C(5)H(10); X = NO(3), R = C(4)H(8)), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, (1)H and (13)C[(1)H] NMR spectroscopies, and also X-ray crystallography (for X = Cl, R(2) = 2Me; X = NO(3), R = C(4)H(8)), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.

Iminoacylation. 3. Formation of platinum(IV)-based metallaligands due to facile one-end addition of vic-dioximes to coordinated organonitriles

The reaction of vic-dioximes with the organonitrile platinum(IV) complexes trans-[PtCl4(RCN)2] (R = Me, CH2Ph, Ph, vic-dioxime = dimethylglyoxime; R = Me, vic-dioxime = cyclohexa-, cyclohepta-, and cyclooctanedione dioximes) proceeds rapidly under relatively mild conditions and affords products of one-end addition of the dioximes to the nitrile carbon, i.e. [PtC4(NH=C(R)ON=[spacer]=NOH)2] (1-6) (R = Me, CH2Ph, Ph, spacer = C(Me)C-(Me) for dimethylglyoxime; R = Me, spacer = C[C4H8]C, C[C5H10]C, C[C6H12]C for the other dioximes), giving a novel type of metallaligand. All addition compounds were characterized by elemental analyses (C, H, N, C1, Pt), FAB mass spectrometry, and IR and 1H, 13C[1H], and 195Pt NMR spectroscopy. X-ray structure determination of the dimethylformamide bis-solvate [PtCl4(NH=C(Me)ON=C(Me)C(Me)=NOH)2] x 2DMF (la) disclosed its overall trans geometry with the dimethylglyoxime part in anti configuration and the amidine one-end (rather than N,N-bidentate) coordination mode of the N-donor ligands. When a mixture of cis- and trans-[PtC4(MeCN)2] in MeCN was treated with dimethylglyoxime, the formation of, correspondingly, cis- and trans-[PtCl4(NH=C(Me)ON=C(Me)C(Me)=NOH)2] (1) was observed and cis-to-trans isomerization in DMSO-d6 solution was monitored by 1H, 2D [1H,15N] HMQC, and 195Pt NMR spectroscopies. Although performed ab initio calculations give evidence that the trans geometry is the favorable one for the iminoacylated species [PtCl4-(ligand)2], the platinum(IV) complex [PtCl4(NH=C(Me)ON=C[C4Hs]C=NOH)2] (4) was isolated exclusively in cis configuration with the two metallaligand "arms" held together by intramolecular hydrogen bonding between the two peripheral OH groups, as it was proved by single-crystal X-ray diffractometry. The classic substitution products, e.g. [PtC12(N,N-dioximato)2] (12-15), are formed in the addition reaction as only byproducts in minor yield; two of them, [PtCl2(C7H11N2O2)2] (14) and [PtCl2(C8H13N2O2)2] (15), were structurally characterized. Complexes (12-15) were also prepared by reaction of the vic-dioximes with [PtCl4L(Me2SO)] (L = Me2SO, MeCN), but monoximes (Me2C=NOH, [C4H8]C=NOH, [C5H10]C=NOH, PhC(H)=NOH, (OH)C6H4C(H)= NOH) react differently adding to [PtCl4(MeCN)(Me2SO)] to give the corresponding iminoacylated products [PtCl4(NH=C(Me)ON=CRR')(Me2SO)](7-11).

Regiospecific Oximato Coordination at the Oxygen Site: Ligand Design and Low-Spin Mn(II) and Fe(II/III) Species

The (pyridylazo)oxime ligand (C(5)H(4)N)N=NC(=NOH)C(6)H(4)R(p), HRL (R = H, Me), has been synthesized with the objective of promoting the very rare mononuclear oximato-O coordination. The synthesis involves hydrazone nitrosation. HRL reacts with M(ClO(4))(2).6H(2)O, affording [M(RL)(2)] (M = Mn, Fe), and X-ray structure determinations have indeed revealed the presence of the desired oximato-O coordination mode in the distorted octahedral MN(4)O(2) sphere characterized by a 2-fold axis of symmetry relating the two tridentate ligands, all chelate rings being five-membered. The M-N and M-O distances are relatively short (1.84-1.99 Å), consistent with spin-pairing (M = Mn, S = (1)/(2); M = Fe, S = 0). The M-N bond length trend, Mn(II) > Fe(II), is in accord with the larger radius of the low-spin Mn(II) atom. The M-O length order is, however, Mn(II) < Fe(II). This reversal occurs because of the rigidity of the ligand skeleton. Significant M-azo back-bonding is present (N=N length approximately 1.30 Å). [Mn(RL)(2)] displays hyperfine-split axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.06, A( parallel) approximately 170 G, A( perpendicular) approximately 65 G) in frozen solution as well as in polycrystalline [Fe(RL)(2)] lattices. The quasireversible Fe(III)/Fe(II) couple of [Fe(RL)(2)] has E(1/2) approximately 0.7 V. The oxidized complex [Fe(RL)(2)]PF(6) has been electrosynthesized. It is low-spin (S = (1)/(2)) and displays axial EPR spectra (g( parallel) approximately 1.98, g( perpendicular) approximately 2.14) in frozen solution. The Mn(II) --> Mn(III) oxidation ( approximately 1.0 V) in [Mn(RL)(2)] is irreversible. Crystal data for [Mn(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.142(7) Å, b = 10.721(7) Å, c = 16.933(10) Å, beta = 93.01(4) degrees, Z = 4. Crystal data for [Fe(HL)(2)].CH(2)Cl(2): crystal system monoclinic, space group I2/a, a = 14.254(6) Å, b = 10.742(6) Å, c = 16.719(8) Å, beta = 92.35(4) degrees, Z = 4.

Iminoacylation. 1. Addition of Ketoximes or Aldoximes to Platinum(IV)-Bound Organonitriles

The metal-mediated iminoacylation reaction of ketoximes or aldoximes upon treatment with the organonitrile platinum(IV) complexes trans-[PtCl(4)(RCN)(2)] proceeds under relatively mild conditions in acetonitrile (R = Me) or in chloroform (R = CH(2)Ph, Ph) to give trans-[PtCl(4)(NH=C(R)ON=CR(1)R(2))(2)] (R(1) = R(2) = Me; R(1)R(2) = C(4)H(8), R(1)R(2) = C(5)H(10), R(1)R(2) = (H)Ph, R(1)R(2) = (H)C(6)H(4)(OH)-o; 1-14) in 90-95% yield. All these compounds were characterized by elemental analyses (C, H, N, Cl, Pt), FAB mass spectrometry, and IR and (1)H, (13)C{(1)H}, and (195)Pt NMR spectroscopies. X-ray structure determinations of [PtCl(4)(NH=C(Me)ON=CMe(2))(2)] (1) and [PtCl(4){NH=C(Me)ON=C(C(5)H(10))}(2)] (3) disclosed their overall trans-configuration and the amidine one-end rather than N,N-bidentate coordination mode of the N-donor ligands. The iminoacyl species are in E-conformation which is held by a rather weak N-H.N hydrogen bond between the amidine =NH atom and the oxime nitrogen with the following observed distances and angles for 1 and [3]: N(1).N(2), and N(1)-H, N(1)H.N(2) are 2.605 [2.592], 0.74 [0.71], and 2.20 [2.25] Å; N(1)-H.N(2) is 115 degrees [111 degrees ]. No evidence of the Z-conformation in solution was obtained by NMR spectroscopy. Compounds trans-[PtCl(4)(NH=C(R)ON=CR(1)R(2))(2)] are unexpectedly stable toward hydrolysis both in the solid state and in solutions.