David T. Hill

Interactions Of Porphyrins With Purified DNA And More Highly Organized Structures

Studies of the solution properties of gold(III)tetrakis(4-N-methylpyridyl) porphine and its DNA binding characteristics have been conducted utilizing uv/vis absorption spectroscopy, circular dichroism (CD), Mossbauer spectroscopy, and temperature-jump relaxation techniques. These studies indicate that over the concentration range considered this water soluble gold(III) porphyrin does not aggregate, binds axial ligands only weakly with a preference for soft Lewis bases, and is capable of intercalation into nucleic acids of appropriate base pair content. The interaction of this and several other porphyrins with the synthetic polynucleotide poly(dA-dC).poly(dT-dG) has been studied. Spectroscopic signatures for intercalation were found for those derivatives not having axial ligands. Intercalation into chromatin in vitro can also occur with those porphyrins and metalloporphyrins which do not have axial ligands. Finally, studies utilizing microinjection techniques indicate that once within the cell, tetrakis(4-N-methylpyridyl)porphine tends to localize in the nucleus.

Interactions of gold coordination complexes with DNA

The interactions of certain gold(I) and gold(III) complexes with isolated plasmid pBR322 DNA were defined and compared to those of cis-diamminedichloroplatinum(II), CDDP, using an agarose gel electrophoresis assay. Trichloro(pyridine)gold(III) appeared to bind to DNA as evidenced by its ability to produce dose-dependent changes in the electrophoretic mobilities of closed circular, supercoiled, closed circular, relaxed, and open circular plasmid DNAs. These effects suggest that the gold containing complex induces conformational changes in the plasmid as a result of the compound binding to the DNA and the subsequent unwinding of the double helix and shorting of the DNA. Auranofin [(2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S)-triethyl phosphine gold(I)] did not appear to interact with DNA under any conditions. However, its analog chloro(triethylphosphine) gold(I) interacted with DNA at pH 9.5 in borate buffer and produced electrophoretic mobility changes in pBR322 DNA which were different from those produced by the gold(III) complexes that were evaluated. Binding of chloro(triethylphosphine) gold(I) was inhibited by the co-addition of the thiosugar portion of auranofin suggesting preferential binding of the gold moiety to thiosugar, which results in the production of auranofin (or a sugar containing) gold complex and inhibition of gold binding to DNA. The interactions of a number of gold compounds with DNA were also evidenced by their abilities to inhibit the binding of ethidium bromide to DNA. The results from these studies indicate that: gold containing complexes can bind to, and produce conformational changes in, DNA; gold(I) and gold(III) complexes may interact with DNA via different chemical mechanisms to produce different conformational changes in DNA; and certain coordinating ligands in gold complexes (e.g. Cl, Br and SCN) can be exchanged for binding sites on DNA by gold.

Synthesis and X-ray crystal structure determination of two pseudopolymorphic forms of μ-[1,2-bis(diphenylphosphino)ethane] bis [chlorogold(I)]: a digold(I) DNA binder

Abstract An improved synthetic route to the linearly coordinated digold(I) complex, μ-[1,2-bis(diphenylphosphino)ethane]bis[chlorogold(I)], is reported. This complex crystallizes in two pseudopolymorphic forms from a chloroform/methylene chloride solution; the crystal and molecular structures of both are discussed and compared. In both crystal forms the potentially chelating diphenylphosphinoethane (dppe) ligand instead coordinates to two separate gold atoms. The coordination environment of each gold atom is linear in both pseudopolymorphs and the structures display normal goldchloride and goldphosphorus bond distances. On the molecular level, the pseudopolymorphs differ fundamentally by a twist about one of the gold phosphorous bonds with the phosphorous atoms of the dppe ligand adopting a transoid orientation relative to one another in both polymorphs. These conformations thus place the intramolecular gold atoms 6 A apart and preclude intramolecular AuAu bonding interactions. As has been observed for related gold(I) complexes there are short intermolecular AuAu contacts of the order of 3.2 A present in both structures. The conformational flexibility of the gold complex relative to its observed biological activity as a DNA binder is discussed.

Seleno-auranofin (Et3PAuSe-tagl): synthesis, spectroscopic (EXAFS, 197Au Mössbauer, 31P, 1H, 13C, and 77Se NMR, ESI-MS) characterization, biological activity, and rapid serum albumin-induced triethylphosphine oxide generation.

Seleno-auranofin (SeAF), an analogue of auranofin (AF), the orally active antiarthritic gold drug in clinical use, was synthesized and has been characterized by an array of physical techniques and biological assays. The Mössbauer and extended X-ray absorption fine structure (EXAFS) parameters of the solid compound demonstrate a linear P-Au-Se coordination environment at a gold(I) center, analogous to the structure of auranofin. The (31)P, (13)C, and (1)H NMR spectra of SeAF in chloroform solution closely resemble those of auranofin. The (77)Se spectrum consists of a singlet at 481 ppm, consistent with a metal-bound selenolate ligand. The absence of (2)J(PSe) coupling in the (31)P and (77)Se spectra may arise from dynamic processes occurring in solution or because the (2)J(PSe) coupling constants are smaller than the observed bandwidths. Electrospray ionization mass spectrometry (ESI-MS) spectra of SeAF in 50:50 methanol-water exhibited strong signals for [(Et(3)P)(2)Au](+), [(Et(3)PAu)(2)-mu-Se-tagl](+), and [Au(Se-tagl)(2)](-), which arise from ligand scrambling reactions. Three assays of the anti-inflammatory activity of SeAF allowed comparison to AF. SeAF exhibited comparable activity in the topically administered murine arachadonic acid-induced and phorbol ester-induced anti-inflammatory assays but was inactive in the orally administered carrageenan-induced assay in rats. However, in vivo serum gold levels were comparable in the rat, suggesting that differences between the in vivo metabolism of the two compounds, leading to differences in transport to the inflamed site, may account for the differential activity in the carrageenan-induced assay. Reactions of serum albumin, the principal transport protein of gold in the serum, demonstrated formation of AlbSAuPEt(3) at cysteine 34 and provided evidence for facile reduction of disulfide bonds at cysteine 34 and very rapid formation of Et(3)P=O, a known metabolite of auranofin.

D and L-N-[(1-benzyl-1H-imidazol-5-yl)-alkyl]-amino acids as angiotensin II AT-1 antagonists

Abstract A series of D and L-N-[(1-benzyl-1H-imidazol-5-yl)-alkyl]-aromatic amino acids ( 2 to 9 ) and several achiral analogs ( 1,10,11 ) were found to be potent AII antagonists (nM range). Among chiral pairs the D isomer had the highest affinity for the binding site. A D-phenylalanine analog, 3 , was the most potent (IC 50 3.8 nM) and had activity in vivo similar to SK&F 108566 when given i.v. but was only marginally active when given i.d.

Evaluation of some tetraalkylammonium gold(I) and gold(III) aurate salts for oral antiinflammatory and antiarthritic activity

Abstract A series of four tetraalkylammonium gold(III) salts, [R 4 N] + [AuX 4 ] − (R  Et, Bu; X  Cl,Br) and five tetraalkylammonium gold(I) salts, [R 4 N] + - [AuX 2 ] − [R  Et, Bu; X  Cl, Br, C 6 H 5 S, S-Glucose- (OAc) 4 ] were prepared, together with [(Et 3 P) 2 Au + ]- [AuCl 2 ] − ( 16 ) and evaluated for their oral antiinflammatory [Au(III)] and antiarthritic activity [Au(I)] in comparison with the gold compounds auranofin [Et 3 PAuS-Glucose(OAc) 4 ] (AF) and [(Et 3 P) 2 Au] + - Cl − ( 4 ). Synthesis of the complexes [R 4 N] + [AuX 2 ] − (R  Et, Bu; X  Cl, Br) was accomplished by reduction of the corresponding Au(IlI) complex with C 6 H 5 NHNH 2 (X  Cl) or acetone (X  Br). RS − displacement of Br − from [(Bu) 4 N] + [AuBr 2 ] − gave the thiolates [(Bu 4 )N] + [Au(SR) 2 ] − [R  C 6 H 5 ; 2, 3, 4, 6- Glucose(OAc) 4 ]. Admixture in EtOH of [(Et 3 P) 2 Au] + Cl with HAuCl 4 gave 16 . Evaluation of the four Au(Ill) salts in the carrageenan-induced rat paw edema assay at 20 mg of Au/kg showed little antiinflammatory activity on oral administration (p.o.). The five Au( I ) complexes were found to be devoid of significant antiarthritic activity in the adjuvant-induced arthritic rat emodel upon oral administration. Moreover, serum gold levels were below 0.6 μg / ml suggesting poor oral bioavailability. In contrast [(Et 3 P) 2 Au + ] [AuCl 2 ] − ( 16 ) was found to be orally effective with serum Au levels of 5.6 μg /ml and demonstrated significant antiarthritic activity comparable to both AF and the salt 4 .

A potent long-acting imidazole-5-acrylic acid angiotensin II AT-1 receptor antagonist

Abstract SB 203220 (9), the naphthyl analog of SK&F 108566(1), is a potent long-acting AT-1 antagonist. In comparison to 1, which is a competitive antagonist, 9 is a partially unsurmountable antagonist with a slower receptor off-rate, a greater resistance to tissue washout, and is more highly protein bound.