Bioorganometallic Chemistry: Structural Diversity of Organometallic Complexes with Bioligands and Molecular Recognition Studies of Several Supramolecular Hosts with Biomolecules, Alkali-Metal Ions, and Organometallic Pharmaceuticals

Palladium(II) and Platinum(II) Organometallic Complexes with the Model Nucleobase Anions of Thymine, Uracil, and Cytosine: Antitumor Activity and Interactions with DNA of the Platinum Compounds

Pd(II) and Pt(II) complexes with the anions of the model nucleobases 1-methylthymine (1-MethyH), 1-methyluracil (1-MeuraH), and 1-methylcytosine (1-MecytH) of the types [Pd(dmba)(mu-L)]2 [dmba = N,C-chelating 2-((dimethylamino)methyl)phenyl; L = 1-Methy, 1-Meura or 1-Mecyt] and [M(dmba)(L)(L')] [L = 1-Methy or 1-Meura; L' = PPh(3) (M = Pd or Pt), DMSO (M = Pt)] have been obtained. Palladium complexes of the types [Pd(C6F5)(N-N)(L)] [L = 1-Methy or 1-Meura; N-N = N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), or 4,4'-dimethyl-2,2'-bipyridine (Me2bpy)] and [NBu4][Pd(C6F5)(1-Methy)2(H2O)] have also been prepared. The crystal structures of [Pd(dmba)(mu-1-Methy)]2, [Pd(dmba)(mu-1-Mecyt)]2.2CHCl3, [Pd(dmba)(1-Methy)(PPh3)].3CHCl3, [Pt(dmba)(1-Methy)(PPh3)], [Pd(tmeda)(C6F5)(1-Methy)], and [NBu4][Pd(C6F5)(1-Methy)2(H2O)].H2O have been established by X-ray diffraction. The DNA adduct formation of the new platinum complexes synthesized was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by the platinum complexes on plasmid DNA pBR322 were also obtained. Values of IC50 were also calculated for the new platinum complexes against the tumor cell line HL-60. All the new platinum complexes were more active than cisplatin (up to 20-fold in some cases).

New palladium(II) and platinum(II) complexes with the model nucleobase 1-methylcytosine: antitumor activity and interactions with DNA

Palladium and platinum complexes with the model nucleobase 1-methylcytosine (1-Mecyt) of the types [Pd(N-N)(C6F5)(1-Mecyt)]ClO4 [N-N = bis(3,5-dimethylpyrazol-1-yl)methane (bpzm), bis(pyrazol-1-yl)methane (bpzm), N,N,N',N'-tetramethylethylenediamine (tmeda), or 2,2'-bipyridine (bpy)] and [M(dmba)(L')(1-Mecyt)]ClO4 [dmba = N,C-chelating 2-(dimethylaminomethyl)phenyl; L' = PPh(3) (M = Pd or Pt), DMSO (M = Pt)] have been obtained. Palladium and platinum complexes of the types cis-[M(C6F5)2(1-Mecyt)2] (M = Pd or Pt) and cis-[Pd(L')(C6F5)(1-Mecyt)2]ClO4 (L' = PPh(3) or t-BuNC) have also been prepared. The crystal structures of [Pd(bpzm)(C6F5)(1-Mecyt)]ClO4, [Pt(dmba)(DMSO)(1-Mecyt)]ClO4, cis-[Pd(C6F5)2(1-Mecyt)2], and cis-[Pd(t-BuNC)(C6F5)(1-Mecyt)2]ClO4 have been established by X-ray diffraction. There is extensive hydrogen bonding (N-H...O, C-H...F or C-H...O) in all the compounds. There are also intermolecular pi-pi interactions between pyrimidine rings of adjacent chains in [Pd(C6F5)2(1-Mecyt)2]. DNA adduct formation of the new complexes synthesized was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by the complexes on plasmid DNA pBR322 were also obtained. Values of IC(50) were also calculated for the new complexes against the tumor cell line HL-60. At a short incubation time (24 h) almost all new complexes were more active than cisplatin.

UV-induced generation of rare tautomers of allopurinol and 9-methylhypoxanthine — A matrix isolation FTIR study

Monomers of allopurinol and 9-methylhypoxanthine were studied using the matrix isolation technique combined with Fourier transform infrared spectroscopy. The oxo tautomeric forms of both compounds were found to dominate in freshly deposited low-temperature argon matrices. For 9-methylhypoxanthine, a small amount of the hydroxy tautomer was also detected in an Ar matrix before any irradiation. Upon exposure of the matrices to the UV (lambda>230 nm or lambda>270 nm) light, a proton transfer photoreaction converting the oxo forms of both compounds into the corresponding hydroxy tautomers occurred. Generation of conjugated ketenes as minor photoproducts was also observed. For 4(3H)-pyrimidinone (a model compound for both allopurinol and 9-methylhypoxanthine), photoreversibility of the UV-induced oxo --> hydroxy transformation was experimentally proven by direct observation of the back hydroxy --> oxo photoreaction. The substrates (oxo tautomers) and products (hydroxy tautomers) of the observed phototransformations were identified by comparison of their IR spectra with the spectra theoretically predicted at the DFT(B3LYP)/6-31++G(d,p) level. The IR bands in the experimental spectra were assigned to the calculated normal modes.

Enantioselective Synthesis of Ferrocenyl Nucleoside Analogues with Apoptosis-Inducing Activity

[reaction: see text] As a contribution to bioorganometallic chemistry, an enantioselective synthesis of novel carbocyclic nucleoside analogues with a ferroceno-cyclopentene backbone was developed. Diastereoselective cuprate 1,4-addition or Mukaiyama-Michael addition to a planar-chiral enoate (ethyl (E)-2-[2-methoxycarbonyl-ferrocenyl]-acrylate) allowed for the introduction of different side chains (RCH(2)). Other important steps include a Dieckmann cyclization and the attachment of the nucleobase (NB) in an iron-assisted S(N)1 reaction. Some of the target compounds were shown to exhibit significant apoptosis-inducing activity (LD(50) = 10-20 microM) against tumor cells.

Cp*Rh-Based Indicator-Displacement Assays for the Identification of Amino Sugars and Aminoglycosides

Indicator-displacement assays based on the organometallic complex [{Cp*RhCl2}2] (Cp*=pentamethylcyclopentadienyl) and the dye gallocyanine were used to sense amino sugars and aminoglycosides in buffered aqueous solution by conducting UV-visible spectroscopy. The data of three assays at pH 7.0, 8.0, and 9.0 were sufficient to distinguish between the amino sugars galactosamine, glucosamine, mannosamine and the aminoglycosides kanamycin A, kanamycin B, amikacin, apramycin, paromomycin, and streptomycin. Furthermore, the assays were used to characterize mixtures of aminoglycosides and obtain quantitative information about the respective analytes.

Developing the {M(CO)3}+ Core for Fluorescence Applications: Rhenium Tricarbonyl Core Complexes with Benzimidazole, Quinoline, and Tryptophan Derivatives

Tridentate ligands derived from benzimidazole, quinoline, and tryptophan have been synthesized, and their reactions with [NEt4]2[Re(CO)3Br3] have been investigated. The complexes 1-4 and 6 and 7 exhibit fac-{Re(CO)3N3} coordination geometry in the cationic molecular units, while 5 exhibits fac-{Re(CO)3N2O} coordination for the neutral molecular unit, where N3 and N2O refer to the ligand donor groups. The ligands bis(1-methyl-1H-benzoimidazol-2-ylmethyl)amine (L1), [bis(1-methyl-1H-benzoimidazol-2-ylmethyl)amino]acetic acid ethyl ester (L2), [bis(1-methyl-1H-benzoimidazol-2-ylmethy)amino]acetic acid methyl ester (L3), [bis(quinolin-2-ylmethyl)amino]acetic acid methyl ester (L4), 3-(1-methyl-1H-indol-3-yl)-2-[(pyridin-2-ylmethyl)amino]propionic acid (L5), 2-[bis(pyridin-2-ylmethyl)amino]-3-(1-methyl-1H-indol-3-yl)propionic acid (L6), and 2-[bis(quinolin-2-ylmethyl)amino]-3-(1-methyl-1H-indol-3-yl)propionic acid (L7) were obtained in good yields and characterized by elemental analysis, 1D and 2D NMR, and high-resolution mass spectrometry (HRMS). The rhenium complexes were obtained in 70-85% yields and characterized by elemental analysis, 1D and 2D NMR, HRMS, IR, UV, and luminescence spectroscopy, as well as X-ray crystallography for [Re(CO)3(L1)]Br (1), {[Re(CO)3(L2)]Br}2.NEt4Br . 8.5H2O (3(2).NEt4Br . 8.5H2O), [Re(CO)3(L4)]Br (4), and [Re(CO)3(L6)]Br (6). Crystal data for C21H19BrN5O3Re (1): monoclinic, P2(1)/c, a = 13.1851(5) A, b = 16.1292(7) A, c = 10.2689(4) A, beta = 99.353(1) degrees , V = 2154.8(2) A3, Z = 4. Crystal data for C56H73Br3N11O18.50 Re2 (3(2).NEt4Br . 8.5H2O): monoclinic, C2/c, a = 34.7760(19) A, b = 21.1711(12) A, c = 20.3376(11) A, beta = 115.944(1) degrees , V = 13464.5(1) A3, Z = 8. Crystal data for C26H21BrN3O5Re (4): monoclinic, P2(1)/c, a = 16.6504(6) A, b = 10.1564(4) A, c = 14.6954(5) A, beta = 96.739(1) degrees , V = 2467.9(2) A3, Z = 4. Crystal data for C27H24BrN4O5Re (6): monoclinic, P2(1), a = 8.7791(9) A, b = 16.312(2) A, c = 8.9231(9) A, beta = 90.030(1) degrees , V = 1277.8(2) A3, Z = 2.

Carbohydrate–metallocene conjugates: selective formation of a zirconadioxacyclopentane-type dimer from the reaction of a bis(enolate)ZrCp2reagent with a glucofuranoside derivative

The zirconocene enolate complex bis(2-propenolato)ZrCp2 (1) reacts with two molar equivalents of the 1,2,3,4-O-tetramethyl-alpha-D-glucopyranoside (2) with liberation of two equivalents of acetone to yield cleanly the bis(carbohydrate)zirconcene complex (3). Alternatively 1 and the "bifunctional" glucose derivative 3-O-benzyl-1,2-O-isopropylidene-glucofuranoside (4) react to the corresponding zirconadioxacyclopentane-type metallacyclic product that was isolated as the respective dimer (5) featuring a sequence of linearly anellated five-, four-, five-membered metallacycles. Both carbohydrate zirconocene complexes 3 and 5 were characterized by NMR experiments as well as by X-ray diffraction.

Synthesis, structure and assessment of the cytotoxic properties of 2,5-dimethylazaferrocenyl phosphonates

The reaction of lithiated 2,5-dimethylazaferrocene 1 with diethyl chlorophosphate proceeds to give lateral and ring phosphonate products. The products 2 and 3 were characterized by spectroscopic (1H, 31P{1H} NMR, MS, IR) methods and 3 was treated with W(CO)5(thf) to form a crystalline W(CO)5-complex 4 which was characterized by single-crystal X-ray analysis. The new 2,5-dimethylazaferrocenyl phosphonates were transformed into the corresponding N-methyl iodide salts 5 and 6 in quantitative yields. Both salts are water soluble and stable compounds and an analysis of their cytotoxic and anti-proliferative activity was carried out. Compound 6 possesses anti-metabolic activity which exhibited some preference towards the cancerous HeLa cell line over the non-cancerous NIH 3T3 cell line. These new compounds are the first examples of azaferrrocene (i.e. non-ferrocene) derivatives featuring biologically important phosphonate groups. The preliminary studies into cytotoxic activity indicates that as with ferrocene, azaferrocene can also be regarded as a potential source for organometallic anticancer agents, featuring the iron centre in the +2 oxidation state rather than the often utilized ferrocenium +3 species.

Supramolecular chemistry with organometallic half-sandwich complexes

Organometallic half-sandwich complexes of the late transition metals are versatile building blocks for supramolecular chemistry. They can be used to build metallamacrocyclic receptors and coordination cages, to study the adaptive behavior of dynamic combinatorial libraries and to generate indicator displacement assays for the detection of biologically interesting analytes such as peptides and aminoglycosides.

Use of the Sonogashira Coupling Reaction for the “Two-Step” Labeling of Phenylalanine Peptide Side Chains with Organometallic Compounds

The Pd-catalyzed Sonogashira coupling of ferrocene alkyne derivatives as metal probes to iodophenylalanine containing peptides is described. 4-Iodophenylalanine was incorporated into dipeptides and the neuropeptide [Leu5]-enkephalin (Enk) by solid phase peptide synthesis, thereby creating a functional group suitable for the Sonogashira coupling. The reaction with two different ferrocene alkynes resulted in the corresponding ferrocene-labeled derivatives, which were obtained in good yield and purity. All new compounds were comprehensively characterized, including elemental analysis, 1D and 2D NMR, EI-, FAB- or ESI-MS, IR and UV-vis spectroscopy, and electrochemistry of the ferrocene label. Unlike well-established conjugation methods for peptide side chains such as lysine and cystein, the phenyl group in Phe is not readily available for derivatization. This work presents a versatile procedure for the regioselective introduction of an organometallic label into biologically relevant peptides as exemplified for enkephalin.

Controlling ligand substitution reactions of organometallic complexes: tuning cancer cell cytotoxicity

Organometallic compounds offer broad scope for the design of therapeutic agents, but this avenue has yet to be widely explored. A key concept in the design of anticancer complexes is optimization of chemical reactivity to allow facile attack on the target site (e.g., DNA) yet avoid attack on other sites associated with unwanted side effects. Here, we consider how this result can be achieved for monofunctional "piano-stool" ruthenium(II) arene complexes of the type [(eta6-arene)Ru(ethylenediamine)(X)]n+. A potentially important activation mechanism for reactions with biomolecules is hydrolysis. Density functional calculations suggested that aquation (substitution of X by H2O) occurs by means of a concerted ligand interchange mechanism. We studied the kinetics and equilibria for hydrolysis of 21 complexes, containing, as X, halides and pseudohalides, pyridine (py) derivatives, and a thiolate, together with benzene (bz) or a substituted bz as arene, using UV-visible spectroscopy, HPLC, and electrospray MS. The x-ray structures of six complexes are reported. In general, complexes that hydrolyze either rapidly {e.g., X = halide [arene = hexamethylbenzene (hmb)]} or moderately slowly [e.g., X = azide, dichloropyridine (arene = hmb)] are active toward A2780 human ovarian cancer cells, whereas complexes that do not aquate (e.g., X = py) are inactive. An intriguing exception is the X = thiophenolate complex, which undergoes little hydrolysis and appears to be activated by a different mechanism. The ability to tune the chemical reactivity of this class of organometallic ruthenium arene compounds should be useful in optimizing their design as anticancer agents.

Supramolecular architectures assembled by the interaction of purine nucleobases with metal-oxalato frameworks. Non-covalent stabilization of the 7H-adenine tautomer in the solid-state

The synthesis, crystal structure and variable-temperature magnetic measurements of the compounds [Mn(mu-ox)(H2O)(7H-pur-kappaN9)]n (1), {[Mn(mu-ox)(H2O)2].(7H-ade).(H2O)}n (2) and {[Cu(mu-ox)(H2O)(7H-ade-kappaN9)][Cu(mu-ox)(mu-H2O)(7H-ade-kappaN9)]. approximately 10/3H2O}n (3), (where ox: oxalato dianion, pur: purine, and ade: adenine) are reported. Compounds 1and 2 contain one-dimensional chains in which manganese(II) atoms are bridged by bis-bidentate oxalato ligands. The distorted octahedral geometry around each metal centre is completed in compound 1 by one water molecule and the imidazole N9 donor site of the purine ligand, which is a rare example of direct binding between the Mn(II) ion and the N donor site of an isolated nucleobase. Unlike 1, the adenine moiety in compound 2 is not bonded to manganese atoms and the metal coordination polyhedron is filled by two water molecules in a cis-arrangement. Its crystal building is constructed from pi-stacked layers of Watson-Crick hydrogen-bonded adenine...(H2O2)...adenine aggregates and zig-zag Mn(II)-oxalato chains held together by means of a strong network of hydrogen bonding interactions. The nucleobase exists in the lattice as the 7H-adenine tautomer which represents an unprecedented solid-state characterization of this minor tautomer as free molecule (without metal coordination) stabilized through non-covalent interactions. Compound consists of two slightly different [Cu(ox)(H2O)(7H-ade-kappaN9)] units in which the nucleobase coordinates through the imidazole N9 atom. The planar complex entities are parallel stacked and joined by means of long Cu-O bonds involving oxygen atoms from the oxalato and the aqua ligands, giving one-dimensional chains with a [4 + 1] square-planar pyramidal and a [4 + 2] octahedral coordination around the metal centre, respectively. Self-assembled process of compound 3 is further driven by an in-plane network of hydrogen bonding interactions to generate a porous 3D structure containing parallel channels filled by guest water molecules. Variable-temperature magnetic susceptibility measurements of all the complexes show the occurrence of antiferromagnetic interactions between the paramagnetic centres. DFT calculations have been performed to check the influence of packing in the stability of the 7H-amino tautomer of 2 and in the complex geometry of 3.

Organometallic chemistry, biology and medicine: ruthenium arene anticancer complexes

Our work has shown that certain ruthenium(II) arene complexes exhibit promising anticancer activity in vitro and in vivo. The complexes are stable and water-soluble, and their frameworks provide considerable scope for optimising the design, both in terms of their biological activity and for minimising side-effects by variations in the arene and the other coordinated ligands. Initial studies on amino acids and nucleotides suggest that kinetic and thermodynamic control over a wide spectrum of reactions of Ru(II) arene complexes with biomolecules can be achieved. These Ru(II) arene complexes appear to have an altered profile of biological activity in comparison with metal-based anticancer complexes currently in clinical use or on clinical trial.

Supramolecular Assemblies and Molecular Recognition of Amphiphilic Schiff Bases with Barbituric Acid in Organized Molecular Films

A bolaform Schiff base, N,N'-bis(salicylidene)-1,10-decanediamine (BSC10), has been synthesized and its interfacial hydrogen bond formation or molecular recognition with barbituric acid was investigated in comparison with that of a single chain Schiff base, 2-hydroxybenzaldehyde-octadecylamine (HBOA). It has been found that while HBOA formed a monolayer at the air/water interface, the bolaform Schiff base formed a multilayer film with ordered layer structure on water surface. When the Schiff bases were spread on the subphase containing barbituric acid, both of the Schiff bases could form hydrogen bonds with barbituric acid in situ in the spreading films. As a result, an increase of the molecular areas in the isotherms was observed. The in situ H-bonded films could be transferred onto solid substrates, and the transferred multilayer films were characterized by various methods such as UV-vis and FT-IR spectrosopies. Spectral changes were observed for the films deposited from the barbituric acid subphase, which supported the hydrogen bond formation between the Schiff bases and barbituric acid. By measuring the MS-TOF of the deposited films dissolved in CHCl3 solution, it was concluded that a 2:1 complex of HBOA with barbituric acid and a 1:2 complex of BSC10 with barbituric acid were formed. On the other hand, when the multilayer films of both Schiff bases were immersed in an aqueous solution of barbituric acid, a similar molecular recognition through the hydrogen bond occurred. A clear conformational change of the alkyl spacer in the bolaform Schiff base was observed during the complex formation with the barbituric acid.

Synthesis of metal-carbonyl-dendrimer-antibody immunoconjugates: towards a new format for carbonyl metallo immunoassay

We report the preparation of metal-carbonyl-dendrimer-antibody conjugates. These metal-carbonyl-multilabeled antibodies are designed to be used in a new solid-phase-format carbonyl metallo immunoassay (CMIA). A fourth-generation polyamidoamine dendrimer was labeled with 10-25 (eta5-cyclopentadienyl)iron dicarbonyl (eta1-N-succinimidyl) entities. An antibody was chemically modified at its carbohydrate chains by a site-directed process used to preserve the antigen-antibody binding site. The antibody was then coupled with the dendrimer labeled with 10 metal carbonyl groups. An average of 1.4 labeled dendrimers were grafted per antibody molecule. These metal-carbonyl-dendrimer-antibody conjugates were used as new universal detection reagents that recognize their specific antigens. The antigens were spotted onto nitrocellulose membranes and detected by using the conjugates in combination with Fourier transform infrared spectroscopy. A detection level in the range 5-200 pmol per membrane was achieved. This approach opens the way to a new CMIA format.

An Unusual 3D Coordination Polymer Based on Bridging Interactions of the Nucleobase Adenine

The first 3D coordination polymer containing a nucleobase as a bridging ligand, [[Cu2(mu-ade)4(H2O)2][Cu(ox)(H2O)]2 x approximately 14H2O]n (1), has been synthesized by reaction of adenine (Hade) with a basic solution of K2[Cu(ox)2] x 2H2O (ox = oxalato dianion). Compound 1 crystallizes in the trigonal space group R3 with a = b = 31.350(1) angstroms, c = 14.285(1) angstroms, V = 12158.7(10) angstroms3, and Z = 9. X-ray analysis shows a covalent 3D network in which the copper(II) centers are bridged by tridentate mu-N3,N7,N9 adeninate ligands. The compound has relatively large, nanometer-sized tubes associated with the self-assembly process directed solely by metal-ligand interactions. The covalent 3D framework remains intact upon removal of the guest water molecules trapped in the nanotubes. Magnetic measurements indicate an overall antiferromagnetic behavior of the compound.

A nucleic acid base derivative tethered to a ruthenium carbene complex: hydrogen bonded dimers in both the solid state and solution?

A ruthenium carbene bearing a uracil (Ur) substituent has been prepared and has a dimeric structure in the solid state-the dimer being held together by hydrogen bonds between two uracil groups on neighbouring molecules: evidence for the persistence of this interaction in solution has been obtained.

Half-sandwich arene ruthenium(ii)–enzyme complex

The 1.6 [Angstrom] X-ray crystal structure of [(eta(6)-p-cymene)Ru(lysozyme)Cl(2)], the first of a half-sandwich complex of a protein, shows selective ruthenation of Nepsilon of the imidazole ring of His15.

Induced-fit recognition of DNA by organometallic complexes with dynamic stereogenic centers

Organometallic chemistry offers novel concepts in structural diversity and molecular recognition that can be used in drug design. Here, we consider DNA recognition by eta 6-arene Ru(II) anticancer complexes by an induced-fit mechanism. The stereochemistry of the dinuclear complex [((eta 6-biphenyl)RuCl(en))2-(CH2)6]2 + (3, en = ethylenediamine) was elucidated by studies of the half unit [(eta 6-biphenyl)RuCl(Et-en)]+ (2, where Et-en is Et(H)NCH2CH2NH2). The structures of the separated RRu*RN* and SRu*RN* diastereomers of 2 were determined by x-ray crystallography; their slow interconversion in water (t(1/2) approximately 2 h, 298 K, pH 6.2) was observed by NMR spectroscopy. For 2 and 3 the RRu*RN* configurations are more stable than SRu*RN* (73:27). X-ray and NMR studies showed that reactions of 2 and 3 with 9-ethylguanine gave rise selectively to SRu*RN* diastereomers. Dynamic chiral recognition of guanine can lead to high diastereoselectivity of DNA binding. The dinuclear complex 3 induced a large unwinding (31 degrees) of plasmid DNA, twice that of mononuclear 2 (14 degrees), and effectively inhibited DNA-directed RNA synthesis in vitro. This dinuclear complex gave rise to interstrand cross-links on a 213-bp plasmid fragment with efficiency similar to bifunctional cisplatin, and to 1,3-GG interstrand and 1,2-GG and 1,3-GTG intrastrand cross-links on site-specifically ruthenated 20-mers. Complex 3 blocked intercalation of ethidium considerably more than mononuclear 2. The concept of induced-fit recognition of DNA by organometallic complexes containing dynamic stereogenic centers via dynamic epimerization, intercalation, and cross-linking may be useful in the design of anticancer drugs.