Synthesis, Characterisation and Biological Activity of Chiral Platinum(II) Complexes

Benign synthesis of terpene-based 1,4-p-menthane diamine

Terpenes represent a promising renewable feedstock for the substitution of fossil resources in the synthesis of renewable platform chemicals, like diamines. This work describes the synthesis and full characterization of 1,4-p-menthane diamine (1,4-PMD) obtained from α-terpinene (1). A two-step procedure using dibenzyl azodicarboxylate (DBAD) and H2 as rather benign reagents was employed under comparatively mild conditions. Both C-N bonds were formed simultaneously during a visible-light mediated Diels-Alder reaction, which was investigated in batch or flow, avoiding regioselectivity issues during the amination steps that are otherwise typical for terpene chemistry. Heterogeneously catalyzed quadruple hydrogenation of the cycloadduct (2a) yielded 1,4‑PMD (3). While the intermediate cycloadduct was shown to be distillable, the target diamine can be sublimed, offering sustainable purification methods.

Elucidating the Multimodal Anticancer Mechanism of an Organometallic Terpyridine Platinum(II) N-Heterocyclic Carbene Complex against Triple-Negative Breast Cancer In Vitro and In Vivo

Treatment of triple-negative breast cancer (TNBC) has long been a medical challenge because of the lack of effective therapeutic targets. Targeting lipid, carbohydrate, and nucleotide metabolism pathways has recently been proven as a promising option in view of three heterogeneous metabolic-pathway-based TNBC subtypes. Here, we present a multimodal anticancer platinum(II) complex, named Pt(II)caffeine, with a novel mode of action involving simultaneous mitochondrial damage, inhibition of lipid, carbohydrate, and nucleotide metabolic pathways, and promotion of autophagy. All these biological processes eventually result in a strong suppression of TNBC MDA-MB-231 cell proliferation both in vitro and in vivo. The results indicate that Pt(II)caffeine, influencing cellular metabolism at multiple levels, is a metallodrug with increased potential to overcome the metabolic heterogeneity of TNBC.

Antitumor Activity of Pt(II), Ru(III) and Cu(II) Complexes

Metal complexes are currently potential therapeutic compounds. The acquisition of resistance by cancer cells or the effective elimination of cancer-affected cells necessitates a constant search for chemical compounds with specific biological activities. One alternative option is the transition metal complexes having potential as antitumor agents. Here, we present the current knowledge about the application of transition metal complexes bearing nickel(II), cobalt(II), copper(II), ruthenium(III), and ruthenium(IV). The cytotoxic properties of the above complexes causing apoptosis, autophagy, DNA damage, and cell cycle inhibition are described in this review.

Electronic strain effect on Eu(iii) complexes for enhanced circularly polarized luminescence

The structural and electronic strain of ligands promotes the enhancement of the magnitude of circularly polarized luminescence in chiral Eu(iii) complexes.

Synthesis of Camphor-Derived Bis(pyrazolylpyridine) Rhodium(III) Complexes: Structure-Reactivity Relationships and Biological Activity

Two novel rhodium(III) complexes, namely, [Rh^III(X)Cl₃] (X = 2 2,6-bis((4 S,7 R)-7,8,8-trimethyl-4,5,6,7-tetrahydro-1 H-4,7-methanoindazol-3-yl)pyridine or 2,6-bis((4 S,7 R)-1,7,8,8-tetramethyl-4,5,6,7-tetrahydro-1 H-4,7-methanoindazol-3-yl)pyridine), were synthesized from camphor derivatives of a bis(pyrazolylpyridine), tridentate nitrogen-donor chelate system, giving [Rh^III(H₂L*)Cl₃] (1a) and [Rh^III(Me₂L*)Cl₃] (1b). A rhodium(III) terpyridine (terpy) ligand complex, [Rh^III(terpy)Cl₃] (1c), was also synthesized. By single-crystal X-ray analysis, 1b crystallizes in an orthorhombic P2₁2₁2₁ system, with two molecules in the asymmetric unit. Tridentate coordination by the N,N,N-donor localizes the central nitrogen atom close to the rhodium(III) center. Compounds 1a and 1b were reactive toward l-methionine (l-Met), guanosine-5'-monophosphate (5'-GMP), and glutathione (GSH), with an order of reactivity of 5'-GMP > GSH > l-Met. The order of reactivity of the Rh^III complexes was: 1b> 1a > 1c. The Rh^III complexes showed affinity for calf thymus DNA and bovine serum albumin by UV-vis and emission spectral studies. Furthermore, 1b showed significant in vitro cytotoxicity against human epithelial colorectal carcinoma cells. Since the Rh^III complexes have similar coordination modes, stability differences were evaluated by density functional theory (DFT) calculations (B3LYP(CPCM)/LANL2DZp). With (H₂L*) and (terpy) as model ligands, DFT calculations suggest that both tridentate ligand systems have similar stability. In addition, molecular docking suggests that all test compounds have affinity for the minor groove of DNA, while 1b and 1c have potential for DNA intercalation.

A camphor based 1,3-diamine Ru(ii) terpyridine complex: synthesis, characterization, kinetic investigation and DNA binding

A chiral ancillary ligand that has more steric bulk results in an increased reactivity of a ruthenium complex with biomolecules.

Discovery of potent and efficacious pyrrolopyridazines as dual JAK1/3 inhibitors

A series of potent dual JAK1/3 inhibitors have been developed from a moderately selective JAK3 inhibitor. Substitution at the C6 position of the pyrrolopyridazine core with aryl groups provided exceptional biochemical potency against JAK1 and JAK3 while maintaining good selectivity against JAK2 and Tyk2. Translation to in vivo efficacy was observed in a murine model of chronic inflammation. X-ray co-crystal structure determination confirmed the presumed inhibitor binding orientation in JAK3. Efforts to reduce hERG channel inhibition will be described.

Metal complex interactions with DNA

Increasing numbers of DNA structures are being revealed using a diverse range of transition metal complexes and biophysical spectroscopic techniques. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.

Synthesis and analysis of the anticancer activity of platinum(ii) complexes incorporating dipyridoquinoxaline variants

Platinum complexes incorporating variants of dpq were synthesised. Their DNA affinity and cytotoxicity were compared to complexes containing phen variants, revealing unexpected trends in biological activity.

DNA-based aptamer fails as a simultaneous cancer targeting agent and drug delivery vehicle for a phenanthroline-based platinum(II) complex

The sgc8c aptamer is a 41-base DNA oligonucleotide that binds to leukaemia cells with high affinity and specificity. In this work we examined the utility of this aptamer as both a delivery vehicle and an active targeting agent for an inert platinum complex [(1,10-phenathroline)(ethylenediamine)platinum(II)](2+). The aptamer forms a stem-and-loop confirmation as determined by circular dichroism. This conformation is adopted in both water and phosphate buffered saline solutions. The metal complex binds through intercalation into the aptamer's double helical stem with a binding constant of approximately 4.3 × 10(4) M(-1). Binding of the metal complex to the aptamer had a significant effect on the aptamer's global conformation, and increased its melting temperature by 28°C possibly through lengthening and stiffening of the aptamer stem. The effect of the aptamer on the metal complex's cytotoxicity and cellular uptake was determined using in vitro assays with the target leukaemia cell line CCRF-CEM and the off-target ovarian cancer cell lines A2780 and A2780cp70. The aptamer has little inherent cytotoxicity and when used to deliver the metal complex results in a significant decrease in the metal complex's cytotoxicity and uptake. The reason(s) for the poor uptake and activity may be due to the change in aptamer conformation which affects its ability to recognise leukaemia cells.

Cytotoxic platinum(II) intercalators that incorporate 1R,2R-diaminocyclopentane

Twelve metallointercalators of the type [Pt(I(L))(A(L))](2+), where A(L) is either the R,R or S,S enantiomer of 1,2-diaminocyclopentane (DACP) and I(L) is either 1,10-phenathroline, 4-methyl-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline or 3,4,7,8-tetramethyl-1,10-phenanthroline, were synthesised, characterised and the cytotoxicity to the L1210 cell line was determined. The crystal structures of PHENRRDACP and PHENSS were obtained as monoclinic with a space group of P2(1) (a/Å = 11.4966, b/Å = 6.6983, c/Å = 12.0235) and P2(1) (a/Å = 11.5777, b/Å = 7.0009, c/Å = 12.5079), respectively. The R,R enantiomer of 1,2-diaminocyclopentane (RRDACP) produced the most cytotoxic metallointercalators. The most cytotoxic metallointercalators were 56MERRDACP and 47MERRDACP with IC(50) values of 0.16 and 0.17 μM, respectively, in comparison to cisplatin (1 μM).

Identification of the molecular mechanisms underlying the cytotoxic action of a potent platinum metallointercalator

Platinum-based DNA metallointercalators are structurally different from the covalent DNA binders such as cisplatin and its derivatives but have potent in vitro activity in cancer cell lines. However, limited understanding of their molecular mechanisms of cytotoxic action greatly hinders their further development as anticancer agents. In this study, a lead platinum-based metallointercalator, [(5,6-dimethyl-1,10-phenanthroline) (1S,2S-diaminocyclohexane)platinum(II)](2+) (56MESS) was found to be 163-fold more active than cisplatin in a cisplatin-resistant cancer cell line. By using transcriptomics in a eukaryotic model organism, yeast Saccharomyces cerevisiae, we identified 93 genes that changed their expressions significantly upon exposure of 56MESS in comparison to untreated controls (p ≤ 0.05). Bioinformatic analysis of these genes demonstrated that iron and copper metabolism, sulfur-containing amino acids and stress response were involved in the cytotoxicity of 56MESS. Follow-up experiments showed that the iron and copper concentrations were much lower in 56MESS-treated cells compared to controls as measured by inductively coupled plasma optical emission spectrometry. Deletion mutants of the key genes in the iron and copper metabolism pathway and glutathione synthesis were sensitive to 56MESS. Taken together, the study demonstrated that the cytotoxic action of 56MESS is mediated by its ability to disrupt iron and copper metabolism, suppress the biosynthesis of sulfur-containing amino acids and attenuate cellular defence capacity. As these mechanisms are in clear contrast to the DNA binding mechanism for cisplatin and its derivative, 56MESS may be able to overcome cisplatin-resistant cancers. These findings have provided basis to further develop the platinum-based metallointercalators as anticancer agents.

ELECTRONIC SUPPLEMENTARY MATERIAL

The online version of this article (doi:10.1007/s12154-011-0070-x) contains supplementary material, which is available to authorized users.

New enantiopure NHCs derived from camphor

A new class of enantiopure carbene precursors based on cheap camphor has been developed, and a restricted rotation of one N-substituent due to the C-10 methyl group of the camphor skeleton has been found; in situ prepared corresponding carbenes revealed the same behaviour.

Synthesis, characterization, DNA binding and cleavage studies of chiral Ru(II) salen complexes

Interaction of chiral Ru(II) salen complexes (S)-1 and (R)-1 with Calf Thymus DNA (CT-DNA) was studied by absorption spectroscopy, competitive binding study, viscosity measurements, CD measurements, thermal denaturation study and cleavage studies by agarose gel electrophoresis. The DNA binding affinity of (S)-1 (6.25 x 10(3)M(-1)) was found to be greater than (R)-1 (3.0 x 10(3)M(-1)). The antimicrobial studies of these complexes on five different gram (+)/(-) bacteria and three different fungal organisms showed selective inhibition of the growth of gram (+) bacteria and were not affective against gram (-) and fungal organisms. Further, the (S)-1 enantiomer inhibited the growth of organisms to a greater extent as compared to (R)-1 enantiomer.

Chiral platinum(II) metallointercalators with potent in vitro cytotoxic activity

Four platinum(II) metallointercalating complexes of 1,10-phenanthroline (phen) with the chiral ancillary ligands trans-R,R- and trans-S,S-1,2-diaminocyclohexane (R,R- and S,S-dach, respectively), and N,N'-dimethyl-R,R- and N,N'-dimethyl-S,S-1,2-diaminocyclohexane (Me(2)-R,R-dach and Me(2)-S,S-dach, respectively) have been synthesised and characterised. The crystal structure of [Pt(Me(2)-S,S-dach)(phen)](ClO(4))(2)1.5 H(2)O (C(20)H(26)Cl(2)N(4)O(9.5)Pt) has been determined; orthorhombic, space group P2(1)2(1)2(1)(No. 19), a=23.194(8), b=25.131(9), c=8.522(3) A. In vitro cytotoxic assays (IC(50)) in the human bladder cancer cell line 5637 and in the murine leukemia L1210 cell line revealed that [Pt(S,S-dach)(phen)](ClO(4))(2) (0.091 and 0.13 microM, respectively) and [Pt(R,R-dach)(phen)](ClO(4))(2) (0.54 and 1.50 microM, respectively) were more cytotoxic than cisplatin (0.31 and 0.50 microM, respectively) and considerably more cytotoxic than their methylated counterparts, [Pt(Me(2)-R,R-dach)(phen)](ClO(4))(2) and [Pt(Me(2)-S,S-dach)(phen)](ClO(4))(2) (both>23 microM). Chiral discrimination for [Pt(S,S-dach)(phen)](ClO(4))(2) over its R,R-enantiomer was observed in all 13 cancer cell lines investigated. Moreover, [Pt(S,S-dach)(phen)](ClO(4))(2) was more active than cisplatin in all cell lines tested and shows only partial cross-resistance to cisplatin in two cisplatin resistant cell lines.

Degradation of bidentate-coordinated platinum(II)-based DNA intercalators by reduced L-glutathione

We have examined the interaction of [(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (1, 56MESS), [(5-methyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)] (2+) (2, 5MESS), [(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)platinum(II)] (2+) (3, 56MERR), and [(5,6-dimethyl-1,10-phenanthroline)(ethylenediamine)platinum(II)] (2+) (4, 56MEEN) with reduced L-glutathione and L-methionine. Both thiols degrade all four complexes, mainly by displacing the ancillary ligand and forming a doubly bridged dinuclear complex. The degradation half-life of all the complexes with methionine is >7 days, indicating that these reactions are not biologically relevant. The rate of degradation by glutathione appears to be particularly important and shows an inverse correlation to cytotoxicity. The least active complex, 4 (t 1/2 glutathione: 20 h), degrades fastest, followed by 3 (31 h), 2 (40 h), and 1 (68 h). The major degradation product, [bis-mu-{reduced L-glutathione}bis{5,6-dimethyl-1,10-phenanthroline}bis{platinum(II)}] (2+) (5, 56MEGL), displays no cytotoxicity and is excluded as the source of the anticancer activity. Once bound by glutathione, these metal complexes do not then form coordinate bonds with guanosine. Partial encapsulation of the complexes within cucurbit[n]urils is able to stop the degradation process.

Encapsulation of platinum(II)-based DNA intercalators within cucurbit[6,7,8]urils

The partial encapsulation of platinum(II)-based DNA intercalators of the type [Pt(5-Cl-phen)(ancillary ligand)](2+), where 5-Cl-phen is 5-chloro-1,10-phenanthroline and the ancillary ligand is ethylenediamine, (1S,2S)-diaminocyclohexane (S,S-dach) or (1R,2R)-diaminocyclohexane, within cucurbit[n]uril (CB[n], where n is 6, 7 or 8) has been examined by (1)H and (195)Pt NMR and mass spectrometry. For CB[7], the molecule encapsulates over the ancillary ligand of all metal complexes, whether this is ethylenediamine or diaminocyclohexane. For CB[8], encapsulation occurs over the sides of the 5-Cl-phen ligand at low [Pt(5-Cl-phen)(S,S-dach)](2+) (5CLSS) to CB[8] ratios (i.e. 0.25:1) but over the ancillary ligand at higher ratios (i.e. 2:1). For CB[6] binding, 5CLSS exhibits both portal and cavity binding, with the ancillary ligand displaying chemical shifts consistent with fast exchange kinetics on the NMR timescale for portal binding and slow exchange kinetics for cavity binding. Binding constants could not be determined using UV-vis, circular dichroism or fluorescence spectrophotometry, but a binding constant for binding of 5CLSS to CB[6] of approximately 10(5) M(-1) was determined using (1)H NMR. Finally, the effect of CB[n] encapsulation on the cytotoxicity of the metal complexes was examined using L1210 murine leukaemia cells in vitro growth inhibition assays. The cytotoxicity is highly dependent on both the metal complex and the CB[n] size, and whilst CB[7] and CB[8] generally decreased cytotoxicity, it was found that CB[6] increased the cyotoxicity of 5CLSS up to 2.5-fold.

The effect of ancillary ligand chirality and phenanthroline functional group substitution on the cytotoxicity of platinum(II)-based metallointercalators

Fifteen platinum(II)-based metallointercalators have been synthesised that utilise substituted 1,10-phenanthroline (phen) ligands, including 5-chloro-1,10-phenanthroline (5-Cl-phen), 5-methyl-1,10-phenanthroline (5-CH3-phen), 5-amino-1,10-phenanthroline (5-NH2-phen), 5-nitro-1,10-phenanthroline (5-NO2-phen) and dipyrido[3,2-d:2',3'-f]quinoxaline (dpq), and achiral ethylenediamine (en) and the chiral ancillary ligands 1S,2S-diaminocyclohexane (S,S-dach) and 1R,2R-diaminocyclohexane (R,R-dach). Their cytotoxicity in the L1210 murine leukaemia cell line was determined using growth inhibition assays. The most cytotoxic metal complexes are those that contain S,S-dach ancillary ligands and 5-CH3-phen intercalating ligands. One metallointercalator [Pt(5-CH3-phen)(S,S-dach)]Cl2 (5MESS), displays a 5-10-fold increase in cytotoxicity compared to the clinical agent cisplatin. From DNA binding experiments there appears to be no significant difference between any of the metal complexes, indicating that neither DNA binding affinity nor the mode of binding/DNA adduct formed is the sole determinant of the cytotoxicity of this family of platinum(II)-based metallointercalators.