Cyclometalated Complexes of Platinum and Palladium with N-(4-Chlorophenyl)-α-benzoylbenzylideneamine. In Vitro Cytostatic Activity, DNA Modification, and Interstrand Cross-Link Studies

Cyclopalladation of the Prochiral (Di-tert-butyl)(diphenylmethyl)phosphine: Kinetic Lability of the Corresponding (+)-Phosphapalladacyclic Pd−C Bond and the Reluctance of the Phosphine to Bind in a Monodentate Fashion

The ortho palladation of prochiral (di-tert-butyl)(diphenylmethyl)phosphine proceeded readily to give rise to the dimeric complex, di-mu-chlorobis{[(phenyl)(di-tert-butylphosphino)methyl]phenyl-C2, P}dipalladium(II). The (S,S)-(+)-dimer was subsequently obtained by optical resolution with sodium (S)-prolinate. The absolute configuration of the optically resolved (+)-dimer was concluded from the X-ray diffraction studies of the derivatized O,O-acetylacetonate complex. The availability of the (+)-dimer is crucial to the study of the properties of the Pd-C bond. The phosphapalladacycle Pd-C bond exhibited a remarkable thermodynamic stability. It could not be permanently ruptured to give rise to the eta1-P monodentate even in a refluxing acetone solution containing concentrated hydrochloric acid. Instead, the phosphine was noted to fluctuate between the ring closed and opened states via the reversible Pd-C bond cleavage/formation under this condition. Inevitably, this resulted in the racemization of the five-membered organopalladium ring structure. In contrast, such bond cleavage was not observed at room temperature in the absence of HCl. In fact, the phosphine was observed to readily ortho palladate even under conditions not favorable to cyclopalladation. Indeed, the difficulty of isolating the phosphine as a simple eta1-P monodentate coordination complex was further noted by its lack of reactivity toward the N,N-dimethyl-1-(1'naphthyl)ethylaminate palladacycle mu-chloro dimer. Only by enhancing the Lewis acidity of the palladacycle in the form of the positively charged bis(acetonitrile) complex could the phosphine be encouraged to participate in monodentate eta1-P bonding. Even then, this form of coordination was weak and was only observed by NMR spectroscopy.

Synthesis, interaction with double-helical DNA and biological activity of the water soluble complex cis-dichloro-1,2-propylenediamine-N,N,N′,N′-tetraacetato ruthenium (III) (RAP)

The effects exerted by the new complex cis-dichloro-1,2-propylenediaminetetraacetato ruthenium (III), H[RuCl(2)(PDTA-H(2))] [1, RAP], on DNA and cultured tumor cells (ovarian carcinoma TG cell line) were studied. The comparative study of circular dichroism (CD) spectra obtained from DNA and RAP-DNA system evidences the interaction of the complex with DNA. Compound 1 also interacted with tumor TG cells to slow their proliferation rate. BrdU incorporation was enhanced in cells treated with compound 1, as evidenced by a single-cell electrophoresis method (comet assay), in accordance with RAP-induced DNA damage. DNA migration of compound 1-treated cells was similar to that induced by noxious agents other than cross-linking chemicals. The stability of [RuCl(2)(PDTA-H(2))]-DNA binding is suggested by the high degree of damage that persisted after removal of compound 1 from the culture medium.

Synthesis and anticancer activity of cyclopalladated complexes containing 4-hydroxy-acridine

The synthesis and the characterization (elemental analysis, (1)H NMR and X-ray) of the first cyclopalladated complexes containing 4-hydroxyacridinate as complementary ligand are described. 4-Hydroxyacridine acts as a bidentate [N,O] chelating ligand, giving rise to square planar Pd(II) complexes in the coordination of a cyclopalladated fragment of phenylpyridine or phenylpyrimidine, characterized by the presence of two almost coplanar metalated rings. The biological activity studies conducted on these new Pd(II) complexes proved that the phenylpyridine Pd(II) derivative is more efficient than cis-platinum. The intrinsically substitutional inertness of the cyclopalladated ring and the presence of the [N,O] chelated acridine ligand make these systems of particular interest in their promising biological activity.

Guanine and plasmid DNA binding of mono- and trinuclear fac-[Re(CO)3]+ complexes with amino acid ligands

We have synthesized and fully characterized four new complexes comprising the fac-[Re(CO)3]+ moiety and the ligands NH3, L-proline (Pro), or N,N-dimethylglycine (dmGly). The reaction of [Re(H2O)3(CO)3]+ with the two amino acids gives trinuclear complexes of general formula [Re(L)(CO)3]3 (where L = amino acid). We have studied the in vitro behavior of these compounds with guanine and DNA in order to understand whether the cytotoxicity exhibited by certain rhenium complexes based on the fac-[Re(CO)3]+ core is due to the formation of nucleobase complexes and inter- or intrastrand links between DNA bases. We have performed model studies with guanine and studied the structural effects induced by different rhenium(I) tricarbonyl complexes on PhiX174 plasmid DNA by electrophoretic methods. Our results show that rhenium complexes with two available coordination sites interact with plasmid DNA to form a stable adduct that is likely to involve two bases.

Simple Route to the Doubly ortho-Palladated Azobenzenes: Building Blocks for Organometallic Polymers and Metallomesogens

A new class of doubly cyclopalladated complexes, {PdCl(dmf)}2(mu-azb) (1) and {PdCl(dmf)}2(mu-aazb) (2), has been prepared in dimethylformamide (dmf) by reaction of azobenzene (azb) and 4-aminoazobenzene (aazb), respectively, with an excess of PdCl2(CH3CN)2 complex. Recrystallization of 1 and 2 in dimethyl sulfoxide (dmso) yields complexes {PdCl(dmso)}2(mu-azb) (3) and {PdCl(dmso)}2(mu-aazb) (4), respectively. The crystal structures of 1 and 4 have been determined by X-ray diffraction. All complexes are characterized by 1H and 13C NMR spectra and elemental analysis. In both crystal structures, solvent molecules are bound to palladium through oxygen atoms and oriented trans to carbon. In view of greater preference of palladium to nitrogen and sulfur atoms, the experimental structures were rationalized by quantum-chemical calculations and confirmed as the most stable isomers.

Chiral cyclopalladated complexes derived from N,N-dimethyl-1-phenethylamine with bridging bis(diphenylphosphine)ferrocene ligand as inhibitors of the cathepsin B activity and as antitumoral agents

Chiral cyclopalladated complexes derived from N,N-dimethyl-1-phenethylamine and the coordinating ligand 1,1'-bis(diphenylphosphine)ferrocene were synthesized and studied as Cathepsin B inhibitors and antitumoral agents against solid tumors. Our results revealed that the palladium compound [Pd2(C2,N-S(-)dmpa)2(mu-dppf)Cl2] (2) was able to inhibit Cathepsin B activity in a reversible fashion. This palladacycle compound binds to free cathepsin B (E) as well as to the enzyme-substrate complex (ES) with dissociation constants of KH=12+/-1 microM and alphaKH=2.4+/-0.3 microM, respectively. The application of this complex, in Walker tumor-bearing rats, resulted in 90% inhibition of the tumor growth. Subcutaneous inoculations of 10(6) tumoral cells produced solid tumors with a mass of 4.0+/-1.0 g in 12 days Walker tumor-bearing rats. However, when these animals were treated with one dose of the palladacycle compound (2.0 mg/kg), the tumoral mass was reduced to 0.3+/-0.1 g. On the other hand, the same complex (2) did not afford any protection to mice bearing the non-metastatic Ehrlich Ascites tumor treated with doses of 0.5, 5.0, and 30 mg/kg for a period of four, three and one day, respectively, beginning 72 h after tumor inoculation. Toxicological studies using mice treated with one high dose of the complex (2) (100 mg/kg) did not show any alterations in red and white blood cell morphology 14 days after the drug administration. Similar results were obtained with hepatic, kidney, and spleen tissues. The results presented in this work introduce the title cyclopalladated complexes as promising antitumoral drugs with reduced toxicity in experimental studies.

Synthesis, Structural Characterization, and Photophysical Properties of Palladium and Platinum(II) Complexes Containing 7,8-Benzoquinolinate and Various Phosphine Ligands

A series of mononuclear cyclometalated benzo[h]quinolinate platinum and palladium(II) complexes with phosphine ligands, namely, [M(bzq)ClL] (L=PPh2H, Pt 1, Pd 2; PPh2CCPh, Pt 3, Pd 4), [Pt(bzq)(PPh2H)(PPh2CCPh)]ClO4 5, [Pt(bzq)(PPh2C(Ph)=C(H)PPh2)]ClO4 6, and [Pt(bzq)(CCPh)(PPh2CCPh)] (7a, 7b), were synthesized. The X-ray crystal structures of 1, 6.CH3COCH3.1/2CH3(CH2)4CH3, and 7b.CH3COCH3 have been determined. In 1, the metalated carbon atom and the P atom are mutually cis, whereas in 7b they are trans located. For complex 6, C and N are crystallographically indistinguishable. Reaction of [Pt(bzq)(mu-Cl)]2 with PPh2H and excess of NEt3 leads to the phosphide-bridge platinum dimer [Pt(bzq)(mu-PPh2)]2 8 (X-ray). Moderate pi-pi intermolecular interactions and no evident Pt-Pt interactions are found in 1, 7b, and in 8. All of the complexes exhibit absorption bands at high energy due to the intraligand transitions (1IL pi --> pi) and absorptions at lower energy which are attributed to MLCT (5d) pi --> pi (CLambdaN) transition. Platinum complexes show strong luminescence in both solid state and frozen solutions. The influence of the coligands on the photophysics of the platinum complexes has been examined by absorption and emission spectroscopy.

Studies on the interaction of altromycin B and its platinum(II) and palladium(II) metal complexes with calf thymus DNA and nucleotides

The interaction of the anticancer antibiotic altromycin B and its isostructrural Pt(II) and Pd(II) metal complexes with native calf thymus (CT) DNA was studied using UV-thermal denaturation experiments, circular dichroism spectroscopy and temperature controlled spectrophotometric titrations. Altromycin B stabilizes the double helix by raising the T(m), mainly by intercalation of its chromophore between the base pairs and interacting electrostatically via its sugar moieties with the edges of the DNA helix. Moreover, altromycin B induces a B-->A structural transition of CT DNA. The effect on DNA stability and conformation depends on the metal ion. Pt(II) and Pd(II) complexes induce the B-->A structural transition and stabilize the double helix similarly but they present lower final hyperchromicity due to premelting effects which were caused by intra- and interstrand crosslinking. Thus, a synergic effect of the metal ions to altromycin B-CT DNA interaction is observed in both cases. Altromycin B interacts with 5'-GMP, 5'-AMP and 5'-CMP by electrophilic attack of the opened epoxide ring to the N(7)G, N(1)/N(7)A and N(3)C. Thus, covalent binding between these nucleotides and altromycin B takes place and explain the multiple binding mode suggested by the studies of the interaction of altromycin B and its complexes with DNA. The [Pd(II)-altroB] complex dissociates in the presence of the nucleotides, and various species of Pd(II)-nucleotide complexes, especially with 5'-GMP, are formed. The [Pt(II)-altroB] complex dissociates too, but only one or two species of Pt(II)-nucleotide complexes are formed, and in the case of 5'-AMP interaction the formation of a tertiary altroB-Pt(II)-5'AMP complex is proposed. 5'-TMP reacts very weakly in comparison with the other three nucleotides. These interactions were followed by 1H-NMR.