Biological activity and coordination modes of copper(II) complexes of Schiff base-derived coumarin ligands.

The coordination modes of copper(II) complexes of Schiff base-derived coumarin ligands, which had previously shown good anti-Candida activity, were investigated by pH-potentiometric and UV-Vis spectroscopic methods. These studies confirmed the coordination mode of the ligands to be through the N of the imine and deprotonated phenol of the coumarin-derived ligand in solution. In addition, the more active complexes and their corresponding ligands were investigated in the presence of copper(II) in liquid and frozen solution by ESR spectroscopic methods. A series of secondary amine derivatives of the Schiff base ligands, were isolated with good solubility characteristics but showed little anti-Candida activity. However, cytotoxicity studies of the secondary amines, together with the copper complexes and their corresponding ligands, against human colon cancer and human breast cancer cells identified the chemotherapeutic potential of these new ligands.

Doubly pyrazolate-bridged dinuclear complexes of a highly constrained bis-terdentate ligand: observation of a [high spin-low spin] state for [Fe(II)2(PMAP)2][SbF6]2.2.25(C3H8O) (PMAP = 3,5-bis{[N-(2-pyridylmethyl)amino]-methyl}-1H-pyrazolate).

The bis-terdentate pyrazole-based ligand 3,5-bis{[N-(2-pyridylmethyl)amino]methyl}-1H-pyrazole (PMAPH) was synthesized from 3,5-(1H)-pyrazoledicarbaldehyde and 2 equiv of 2-(aminomethyl)pyridine, using sodium borohydride to reduce the imine intermediate. A family of dinuclear complexes [M(II/III)(2)(PMAP)(2)](X)(2/4) was prepared by 2:2:2 reactions of MX(2)/PMAPH/base, where M = Zn(II) and X = BF(4)(-); M = Cu(II) and X = ClO(4)(-), BF(4)(-), OAc(-), NO(3)(-); M = Ni(II), Fe(III) and X = ClO(4)(-), BF(4)(-); M = Fe(II) and X = SbF(6)(-). Single crystal X-ray structure determinations on four complexes: [Fe(III)(2)(PMAP)(2)](BF(4))(4).2MeCN, [Ni(II)(2)(PMAP)(2)](ClO(4))(2).2MeCN, [Cu(II)(2)(PMAP)(2)](BF(4))(2).2MeCN, and [Zn(II)(2)(PMAP)(2)](BF(4))(2).2MeCN confirmed a dinuclear doubly pyrazolate-bridged structure for each. The two metal centers in these complexes have similar N(6) distorted octahedral coordination spheres, with all donors provided by the two deprotonated PMAP(-) ligands. Magnetic measurements reveal intra-dinuclear antiferromagnetic interactions for both the M = Cu(II) and Ni(II) [M(2)(PMAP)(2)](BF(4))(4) complexes, with J/k(B) = -252(2) K and J/k(B) = -24.7(2) K (H = -2JS(M)S(M)), respectively. Interestingly magnetic measurements show that the complex [Fe(2)(II)(PMAP)(2)](SbF(6))(2).2.25(C(3)H(8)O) is in a mixed high spin (HS)-low spin (LS) spin state, [HS-LS], from 300 to 1.8 K, with no sign of spin crossover to a fully low spin form [LS-LS] even at 1.8 K.

Copper(II) complexes of coumarin-derived Schiff bases and their anti-Candida activity.

The condensation of 7-amino-4-methyl-coumarin (1) with a number of substituted salicylaldehydes yielded a series of Schiff bases (2a-2k) in good yields. Subsequent reaction of these ligands with copper(II) acetate yielded Cu(II) complexes (3a-3k) and some were characterised using X-ray crystallography. All of the free ligands and their metal complexes were tested for their anti-Candida activity. A number of the ligands and complexes exhibited anti-Candida activity comparable to that of the commercially available antifungal drugs, ketoconazole and Amphotericin B.

Role of cell cycle events and apoptosis in mediating the anti-cancer activity of a silver(I) complex of 4-hydroxy-3-nitro-coumarin-bis(phenanthroline) in human malignant cancer cells.

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of 4-hydroxy-3-nitro-coumarin (hncH), and the mixed-ligand silver (I) complex of 4-oxy-3-nitro-coumarin-bis(phenanthroline), [Ag(hnc)(phen)(2)] using four human-derived model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could decrease the proliferation of all four cell lines including neoplastic renal and hepatic, namely A-498 and HepG(2) cells, respectively, along with two non-neoplastic renal and hepatic cell lines, HK-2 and Chang, respectively. Furthermore, non-neoplastic hepatic cells (Chang) appeared to be less sensitive to the effect of the complex, but this effect was not replicated in the non-neoplastic renal (HK-2) cells. Based on IC(50) values [Ag(hnc)(phen)(2)] was shown to be almost four times more potent than cisplatin, using HepG(2) cells. In addition, the observed anti-proliferative effect was shown to be both dose- and time-dependent. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease anti-proliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein] showed that cell death appeared to result from apoptosis, with the possibility of secondary necrosis. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Ag(hnc)(phen)(2)] has been shown to be a more potent anti-proliferative agent than cisplatin, capable of altering key biochemical events leading to cell death. Additional mechanistic studies are underway to probe more fully its mechanism of action.

High and low spin mononuclear and dinuclear iron(II) complexes of 4-amino and 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazoles.

The first dinuclear iron(II) complexes of any 4-substituted 3,5-di(2-pyridyl)-4H-1,2,4-triazole ligands, [Fe(II)2(adpt)2(H2O)1.5(CH3CN)2.5](BF4)4 and [Fe(II)2(pldpt)2(H2O)2(CH3CN)2](BF4)4, are presented [where adpt is 4-amino-3,5-di(2-pyridyl)-4H-1,2,4-triazole and pldpt is 4-pyrrolyl-3,5-di(2-pyridyl)-4H-1,2,4-triazole]. Both dinuclear complexes feature doubly triazole bridged iron(II) centers that are found to be [high spin-high spin] at all temperatures, 4-300 K, and to exhibit weak antiferromagnetic coupling. In the analogous monometallic complexes, [Fe(II)(Rdpt)2(X)2](n+), the spin state of the iron(II) center was controlled by appropriate selection of the axial ligands X. Specifically, both of the chloride complexes, [Fe(II)(adpt)2(Cl)2] x 2 MeOH and [Fe(II)(pldpt)2(Cl)2] x 2 MeOH x H2O, were found to be high spin whereas the pyridine adduct [Fe(II)(adpt)2(py)2](BF4)2 was low spin. Attempts to prepare [Fe(II)(pldpt)2(py)2](BF4)2 and the dinuclear analogues [Fe(II)2(Rdpt)2(py)4](BF4)4 failed, illustrating the significant challenges faced in attempts to develop control over the nature of the product obtained from reactions of iron(II) and these bis-bidentate ligands.

Tricopper(II) complexes of unsymmetrical macrocycles incorporating phenol and pyridine moieties: the development of two stepwise routes.

Two stepwise approaches to preparing large unsymmetrical macrocycles incorporating diethylenetriamine lateral units are described: the first utilises protecting group chemistry, whereas the second exploits irreversible amide bond formation in the presence of an excess of the amine. In the first approach condensation of two equivalents of N-acetyldiethylenetriamine 1 with 2,6-diformyl-4-methylphenol, followed by a sodium borohydride reduction of the newly formed imine bonds and acidic removal of the protecting groups, yields a phenol-containing "two-armed" precursor as an HCl salt 2. Using the second approach the new pyridine-containing "two-armed" precursor , is prepared from 2,6-dimethylpyridinedicarboxylate and an excess of diethylenetriamine. These two "two-armed" di-primary amine precursors, 2 (after reaction with KOH) and 3, can be condensed with the dicarbonyl head units of choice. The lead templated condensation of 2 with 2,6-diacetylpyridine results in the formation of the macrocyclic dilead(II) complex {[Pb(II)(2)(L1)(Cl)](ClO(4))(2)}(infinity) 4. Transmetallation of 4 with three equivalents of copper(II) perchlorate produces Cu(II)(3)(L1)(OH)(ClO(4))(4) 5. Condensation of 3 with 2,6-diacetylpyridine or 2,6-diformylpyridine in the presence of barium(ii) ions results in the macrocyclic complexes [Ba(II)(H(2)L2)](ClO(4))(2) 6 and [Ba(II)(H(2)L3)](ClO(4))(2) 7, respectively. Copper(II) acetate templates the formation of the crystallographically characterised unsymmetrical macrocyclic complex [Cu(II)(3)(L4)(OH)(NCS)(2)].EtOH, 8.EtOH, from 3, 2,6-diformyl-4-methylphenol and NaNCS.

Apoptotic cell death: a possible key event in mediating the in vitro anti-proliferative effect of a novel copper(II) complex, [Cu(4-Mecdoa)(phen)(2)] (phen=phenanthroline, 4-Mecdoa=4-methylcoumarin-6,7-dioxactetate), in human malignant cancer cells.

The central objective of the current study was to investigate the potential in vitro anti-proliferative effect of the parent ligand, 4-methylcoumarin-6,7-dioxyacyeic acid (4-MecdoaH(2)), and its copper (II) complex, bis(phenanthroline4-methylcoumarin-6,7-dioxacetatocopper(II) ([Cu(4-Mecdoa)(phen)(2)]) using four human model cell lines. In addition, selected mechanistic studies were carried out using the most sensitive of the four cell lines. Results obtained show that the complex could alter proliferation of both human neoplastic renal (A-498) and hepatic (HepG2) cells. Furthermore, non-neoplastic hepatic (CHANG) cells appeared to be less sensitive. However, this effect was not duplicated with non-neoplastic renal (HK-2) cells, a profile shared by cisplatin. The observed anti-proliferative effect appeared to be dose-and time-dependent, and could be attributed to the complex, rather than any of the free components i.e. the 1,10-phenanthroline or coumarin ligand, or the simple metal salt. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Based on IC(50) values, [Cu(4-Mecdoa)(phen)(2)] was shown to be almost 12 times more potent than cisplatin. Moreover, there was no evidence that P-glycoprotein-mediated multi-drug resistance was likely to decrease anti-proliferative activity. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein], showed that cell death could switch between apoptosis and necrosis, and this effect appeared to be concentration-dependent. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Cu(4-Mecdoa)(phen)(2)] has been shown to be a more potent anti-proliferative agent than either the ligand or cisplatin, and is capable of altering key biochemical events leading to the execution of apoptotic and/or necrotic cell death, suggesting that it is worthy of further investigation.

Synthesis, characterisation and antimicrobial activity of copper(II) and manganese(II) complexes of coumarin-6,7-dioxyacetic acid (cdoaH2) and 4-methylcoumarin-6,7-dioxyacetic acid (4-MecdoaH2): X-ray crystal structures of [Cu(cdoa)(phen)2].8.8H(2)O and [Cu(4-Mecdoa)(phen)2].13H2O (phen=1,10-phenanthroline).

Two novel coumarin-based ligands, coumarin-6,7-dioxyacetic acid (1) (cdoaH(2)) and 4-methylcoumarin-6,7-dioxyacetic acid (2) (4-MecdoaH(2)), were reacted with copper(II) and manganese(II) salts to give [Cu(cdoa)(H(2)O)(2)].1.5H(2)O (3), [Cu(4-Mecdoa)(H(2)O)(2)] (4), [Mn(cdoa)(H(2)O)(2)] (5) and [Mn(4-Mecdoa)(H(2)O)(2)].0.5H(2)O (6). The metal complexes, 3-6, were characterised by elemental analysis, IR and UV-Vis spectroscopy, and magnetic susceptibility measurements and were assigned a polymeric structure. 1 and 2 react with Cu(II) in the presence of excess 1,10-phenanthroline (phen) giving [Cu(cdoa)(phen)(2)].8.8H(2)O (7) and [Cu(4-Mecdoa)(phen)(2)].13H(2)O (8), respectively. The X-ray crystal structures of 7 and 8 confirmed trigonal bipyramidal geometries, with the metals bonded to the four nitrogen atoms of the two chelating phen molecules and to a single carboxylate oxygen of the dicarboxylate ligand. The complexes were screened for their antimicrobial activity against a number of microbial species, including methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Candida albicans. The metal-free ligands 1 and 2 were active against all of the microbes. Complexes 3-6 demonstrated no significant activity whilst the phen adducts 7 and 8 were active against MRSA (MIC(80)=12.1microM), E. coli (MIC(80)=14.9microM) and Patonea agglumerans (MIC(80)=12.6microM). Complex 7 also demonstrated anti-Candida activity (MIC(80)=22microM) comparable to that of the commercially available antifungal agent ketoconazole (MIC(80)=25microM).

An in vitro investigation of the induction of apoptosis and modulation of cell cycle events in human cancer cells by bisphenanthroline-coumarin-6,7-dioxacetatocopper(II) complex.

The central objective of the current study was to investigate the potential in vitro anti-proliferative properties of the parent ligand, coumarin-dioxy-acetic acid (cdoaH(2)), and its copper complex, copper-coumarin-dioxyacetic acetate-phenathroline ([Cu(cdoa)(phen)(2)]) using four human-derived model cell lines, two neoplastic and two non-neoplastic. In addition, selected mechanistic studies were carried out using one of the neoplastic-derived model cell lines, Hep-G2. Results obtained show that the complex, rather than the ligand, could alter the proliferation of both human neoplastic renal (A-498) and hepatic (Hep-G2) cells. Furthermore, hepatic non-neoplastic cells (Chang) appeared to be less sensitive. However, this effect was not mirrored in non-neoplastic renal (HK-2) cells, a profile shared with cisplatin. The observed anti-proliferative effect appeared to be concentration- and time-dependant, and could be attributed to the complex, rather than any of the component parts, i.e. 1,10-phenanthroline, the coumarin ligand, or the simple metal salt. Furthermore, the complex was shown to decrease DNA synthesis, but did not intercalate with it. Based on IC(50) values, [Cu(cdoa)(phen)(2)] was shown to be almost six times more potent than cisplatin. Moreover, there was no evidence to show that P-glycoprotein (P-gp)-mediated multi-drug resistance (MDR) was likely to play a role in decreasing the anti-proliferative activity of the complex. Cytological stains, analysis of genomic DNA, and biochemical assays [caspase-3 and -9 and cleaved poly(ADP-ribose)-polymerase protein], suggested that cell death could switch between apoptosis and necrosis, and this effect appeared to be concentration-dependent. Additionally, flow cytometric analysis showed that the complex functioned through an alteration in cell cycle progression. Taken together, [Cu(cdoa)(phen)(2)] has been shown to be a more potent anti-proliferative agent than either the ligand or cisplatin, and is capable of altering key biochemical events leading to the execution of apoptotic and/or necrotic cell death, suggesting that it is worthy of further investigation.

Mechanism of action of coumarin and silver(I)-coumarin complexes against the pathogenic yeast Candida albicans.

The anti-fungal activity and mode of action of a range of silver(I)-coumarin complexes was examined. The most potent silver(I)-coumarin complexes, namely 7-hydroxycoumarin-3-carboxylatosilver(I), 6-hydroxycoumarin-3-carboxylatosilver(I) and 4-oxy-3-nitrocoumarinbis(1,10-phenanthroline)silver(I), had MIC80 values of between 69.1 and 4.6 microM against the pathogenic yeast Candida albicans. These compounds also reduced respiration, lowered the ergosterol content of cells and increased the trans-membrane leakage of amino acids. A number of the complexes disrupted cytochrome synthesis in the cell and induced the appearance of morphological features consistent with cell death by apoptosis. These compounds appear to act by disrupting the synthesis of cytochromes which directly affects the cell's ability to respire. A reduction in respiration leads to a depletion in ergosterol biosynthesis and a consequent disruption of the integrity of the cell membrane. Disruption of cytochrome biosynthesis may induce the onset of apoptosis which has been shown previously to be triggered by alteration in the location of cytochrome c. Silver(I)-coumarin complexes demonstrate good anti-fungal activity and manifest a mode of action distinct to that of the conventional azole and polyene drugs thus raising the possibility of their use when resistance to conventional drug has emerged or in combination with such drugs.

Dicopper(II) complexes of a new pyrazolate-containing Schiff-base macrocycle and related acyclic ligand.

Dicopper(II) complexes of two new 3,5-disubstituted-pyrazole-based ligands, bis(quadridentate) macrocyclic ligand (L1)(2-) and bis(terdentate) acyclic ligand (L2)(-), were synthesised by Schiff base condensation of 3,5-diformylpyrazole and either one equivalent of 1,3-diaminopropane or two equivalents of 2-(2-aminoethyl)pyridine in the presence of one or two equivalents of copper(II) ions, respectively. Copper(II) acetate monohydrate was employed in the synthesis of [Cu(2)(L1)(OAc)(2)], [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] and [Cu(II)(2)(L1)(NCS)(2)]; in the last of these one equivalent of NaNCS per copper(II) ion was also added. The fourth complex, [Cu(2)(L2)(NCS)(2)(DMF)]BF(4), was prepared using copper(II) tetrafluoroborate hexahydrate, along with two equivalents of NaOH and six of NaSCN. All four of these dimetallic complexes have been characterised by single crystal X-ray diffraction: the two macrocyclic complexes are the first such Schiff base complexes to be so characterised. A feature common to all four of the structures is bridging of the two copper(II) centres by the pyrazolate moiety/moieties. The structure determinations show that the coordination mode of the acetate groups in both [Cu(2)(L1)(OAc)(2)].2MeOH.H(2)O and [Cu(2)(L2)(H(2)O)(2)(OAc)(3)] is unidentate as had been tentatively predicted by analysis of the infrared spectra (DeltaOCO of 199 and 208 cm(-1), respectively). The magnetochemical studies of the macrocyclic complexes, over the temperature range 4-300 K, revealed strong antiferromagnetic coupling with J = -169 and -213 cm(-1) for [Cu(2)(L1)(OAc)(2)].2H(2)O and [Cu(II)(2)(L1)(NCS)(2)].DMF respectively. The J values have been discussed in relation to a published correlation involving the CuN(pyrazolate)N(pyrazolate) angles.

In vitro anti-tumour and cyto-selective effects of coumarin-3-carboxylic acid and three of its hydroxylated derivatives, along with their silver-based complexes, using human epithelial carcinoma cell lines.

The chemotherapeutic potential of coumarin-3-carboxylic acid (C-3-COOH) and a series of three hydroxylated coumarin-3-carboxylic acid ligands, namely 6-hydroxy-coumarin-3-carboxylic acid (6-OH-C-3-COOH), 7-hydroxy-coumarin-3-carboxylic acid (7-OH-C-3-COOH) and 8-hydroxy-coumarin-3-carboxylic acid (8-OH-C-3-COOH), along with their corresponding silver-based complexes, namely 6-hydroxycoumarin-3-carboxylatosilver (6-OH-C-COO-Ag), 7-hydroxycoumarin-3-carboxylatosilver (7-OH-C-COO-Ag) and 8-hydroxycoumarin-3-carboxylatosilver (8-OH-C-COO-Ag), was determined using two human-derived carcinoma (A-498 and Hep-G2), along with two non-carcinoma human-derived cell lines (CHANG and HK-2). All of the ligands and their silver complexes induced a concentration-dependent cytotoxic effect. Furthermore, hydroxylation of C-3-COOH and its subsequent complexation with silver led to the production of a series of compounds with dramatically enhanced cytotoxicity, with 6-OH-C-3-COO-Ag having the greatest activity. Additionally, all of the metal-based complexes were selectively cytotoxic to both carcinoma-derived cell lines, relative to normal renal and hepatic cells. In comparative studies with cisplatin, and based on the IC(50) values obtained with Hep-G2 cells, it appeared that the coumarin-silver complexes were between 2 and 5.5 times more cytotoxic than cisplatin. All of the coumarin-silver complexes inhibited DNA synthesis, which did not appear to be mediated through intercalation. Furthermore, results obtained from Ames tests showed that all of the test agents and their phase I metabolites were non-mutagenic. Taken together, these findings suggest that both hydroxylation particularly in the 6th position and complexation with silver, served to significantly augment the cytotoxic properties of C-3-COOH, to yield a compound which acts as a cyto-selective agent, as it is a significant killer of cancer, relative to normal cells. We suggest that this group of compounds may have a therapeutic role to play in the successful treatment and management of cancer in man.

A study of the role of apoptotic cell death and cell cycle events mediating the mechanism of action of 6-hydroxycoumarin-3-carboxylatosilver in human malignant hepatic cells.

Previously our research group has studied the anti-proliferative effects of a series of hydroxylated derivatives and silver (I) complexes of coumarin-3-carboxylic acid (C-3-COOH) using two human-derived carcinoma cell lines (A-498 and Hep-G2). Results obtained suggested that both hydroxylation and complexation with silver served to significantly augment the cytotoxic properties of C-3-COOH, to yield a compound, namely 6-hydroxycoumarin-3-carboxylatosilver (6-OH-C-COO-Ag) which could act as a potent and cyto-selective agent, capable of killing cancer cells, and with limited toxicity to cells derived from normal tissue. Here we seek to expand on these findings by probing the molecular mechanism underlying this effect. Results from cytological staining clearly illustrated cellular changes consistent with the induction of apoptotic cell death and which occurred 24 h post-drug-treatment. Additionally, electrophoretic analysis of genomic DNA showed the presence of a ladder pattern, characteristic of apoptotic cell death. This result was subsequently confirmed using a selection of biochemical assays, where increased activity of pro-apoptotic caspases 3 and 9, and increased cleavage of poly(ADP-ribose)-polymerase protein (PARP) were observed. This result was further underpinned by the appearance of a sub-G(1) peak, representing hypo-diploid cells, using flow cytometric analysis. Furthermore, 6-OH-C-COO-Ag was seen to function through an alteration in the percentage of cells entering the G(0)/G(1) phase of cell cycle. Consequently, 6-OH-C-COO-Ag has been shown to a more potent and selective anti-cancer agent than cisplatin, capable of altering key biochemical events leading to the execution of apoptotic cell death as early as 24 h post-treatment, suggesting that it may represent a novel therapeutic agent for the safe and effective treatment of cancer in man.