The 227th ACS National Meeting

Anaheim, CA, March 28-April 1, 2004

CHED 173

DNA-binding studies of potential anticancer rhodium compounds

Szymon Mikulski1, Amity E. Burr1, Shari U. Dunham1, Helen Chifotides2, and Kim R. Dunbar2. (1) Department of Chemistry, Colby College, 5762 Mayflower Hill, Waterville, ME 04901, (2) Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, TX 77842-3012

The DNA-binding properties of a series of dirhodium acetate compounds, Rh2(CH3COO)4(H2O)2, [Rh2(CH3COO)2(CH3CN)6]2+, and Rh2(CF3COO)4(H2O)2 were studied in reactions with double-stranded salmon testes DNA at various compound-to-DNA ratios. Each reaction was arrested and analyzed at regular intervals over a period of 100 hours. Unbound rhodium compound was then removed via centrifiltration. The retentates were analyzed for [DNA] by using UV-vis spectrophotometry, and rhodium content was determined by graphite furnace atomic absorption spectroscopy (GFAAS). The resulting DNA-binding curves generated for the three dirhodium compounds indicate that each compound does bind covalently to duplex DNA and that Rh2(CF3COO)4(H2O)2 has the highest DNA-binding affinity and rate of reaction. Denaturing PAGE experiments have confirmed these DNA-binding results and also indicate that a significant portion of the covalent rhodium-DNA adducts are interstrand cross-links.

CHED 349

Production of significant HOOH concentrations in the deep waters of temperate lakes

Brian Foley and D. Whitney King. Department of Chemistry, Colby College, 5750 Mayflower Hill, Waterville, ME 04901

A continuous flow-injection based, chemiluminescence method was developed to measure H2O2 in Fe(II)-rich freshwater lakes. Vertical profiles of H2O2 concentrations in temperate, thermally stratified, lakes in central Maine exhibited a surface maximum of 600 nM and a deep maximum of 450 nM above the sediment-water interface. Diel cycling was observed for surface H2O2 consistent with photochemical production and biologically mediated decay. The presence of high concentrations of H2O2 in suboxic waters is consistent with dark, abiotic formation of H2O2 from Fe(II) reduction of dissolved oxygen. The formation of H2O2 in the deep water of lakes could have important implications for the redox equilibiria and kinetics of metals in the hypolimnion of many temperate lakes.

CHED 239

Reaction of epichlorohydrin and epibromohydrin with synthetic DNA oligomers

Keith P. Romano and Julie T. Millard. Department of Chemistry, Colby College, 5700 Mayflower Hill Drive, Waterville, ME 04901

Epichlorohydrin (ECH) has a variety of industrial uses, including the manufacture of epoxy resins, agricultural pesticides, adhesives, and plastics. The structure of ECH suggests that it should act as a bifunctional alkylator of DNA, which could account for its mutagenic properties in humans. We are using denaturing polyacrylamide gel electrophoresis (dPAGE) to investigate the reactivity of ECH and the related compound epibromohydrin (EBH) with synthetic DNA oligomers. Both compounds produce a low-mobility band on denaturing gels consistent with an interstrand cross-link. This product is piperidine-cleavable, suggesting alkylation at N7 of guanine. Its rate of formation varies dramatically for ECH and EBH, with the ECH reaction showing a marked pH-dependence. Our research may ultimately shed light on the way in which ECH and similar epoxides disrupt cellular systems.

CHED 424

Phosphate chemistry of potential anticancer ruthenium compounds

Graham M. Poage and Shari U. Dunham. Department of Chemistry, Colby College, 5762 Mayflower Hill, Waterville, ME 04901

The anticancer activity of both the cis and trans isomers of RuCl2(DMSO)4 have been documented by other laboratories. Previous work in our laboratory has shown that cis-RuCl2(DMSO)4 undergoes an apparent dimerization reaction in the presence of inorganic phosphate, whereas the trans isomer does not. In this work, each isomer of RuCl2(DMSO)4 was allowed to react with phosphate buffer under various reaction conditions and screened for products by reversed-phase HPLC. Isolation and characterization of these products will be presented and discussed, particularly with relevance to attenuation of antitumor activity of the parent compounds.

CHED 138

Binding affinities of hMutSa for 6-thioguanine and methyl-6-thioguanine in DNA duplexes: A basis for lesion toxicity

Clara Z. Koh1, Stephen U. Dunham1, Celia Baitinger2, and Paul Modrich2. (1) Department of Chemistry, Colby College, 5763 Mayflower Hill, Waterville, ME 04901, (2) Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710

Cytotoxicity of 6-thioguanine (6SG) is believed to involve incorporation into DNA, methylation to form methyl-6- thioguanine (Me6SG), recognition by the post-replicative mismatch repair system, and persistence of G(2)-M cell cycle arrest leading to cell death. The protein hMutSa is responsible for mismatch recognition, and its relative binding affinities to various thiopurine mismatches were studied. Six variations of 20-mer oligonucleotide duplexes were prepared, in which the central G, on one strand, was substituted with either 6SG or Me6SG and paired with either C or T on a biotin-labeled complementary strand. Single-stranded oligonucleotides were characterized with ESI MS and HPLC analysis of enzymatic digestions. Surface Plasmon Resonance (SPR) Spectroscopy was used to measure their relative binding affinities with hMutSa. These results revealed that, within this DNA sequence context, hMutSa has a preference in the order of 6SGT > GT > Me6SGC > Me6SGT >>> GC > 6SGC.

CHED 469

Synthesis of a tetradentate sulfur ligand and new biomimetic molybdenum and nickel complexes of that ligand

Rebecca R. Conry, Jessica H. Hayward, and Laura L. Olenick. Department of Chemistry, Colby College, 5764 Mayflower Hill, Waterville, ME 04901

The syntheses of novel biomimetic sulfur-ligated complexes that are potential models for metalloenzymes, such as the nickel hydrogenases and molybdenum oxidases, are being pursued. These complexes can be used to determine the basic inorganic chemistry of a metal ion in a similar ligand environment to the appropriate metalloenzyme. The target complexes will incorporate the new tetradentate bisthiolate, bisthioether ligand L that also contains two biphenyl groups. The synthesis of L takes five steps and begins with biphenyl. The synthesis and characterization of L will be discussed, along with any molybdenum or nickel complexes of this ligand that have been prepared.

CHED 906

Synthetic approaches to a highly functionalized indanone metabolite

Meredith S. Collins and Dasan M. Thamattoor. Department of Chemistry, Colby College, 5750 Mayflower Hill, Waterville, ME 04901

The densely functionalized indanone 1 is a naturally occurring metabolite isolated from the filamentous marine cyanobacterium Lyngbya majuscula. Compound 1 is known to be an in vitro inhibitor of the hypoxia-induced activation of the vascular endothelial growth factor (VEGF) gene promoter in Hep3B human liver tumor cells. It thus appears to have a role in affecting tumor angiogenesis. In this work, the progress made toward the total synthesis of 1 is described.

CHED 829

Laser flash photolysis study of dihalocarbenes in room temperature ionic liquids

Jeffrey H. Goldberg, Timothy R. Newhouse, Adelajda Zorba, and Dasan M. Thamattoor. Department of Chemistry, Colby College, 5750 Mayflower Hill, Waterville, ME 04901

There appears to be no report to date of the photochemistry of dihalocarbenes in room temperature ionic liquids (RTIL). This work will describe the results of time resolved laser flash photolysis (LFP) studies of selected dihalocarbenes, generated in RTIL, from the photolysis of precursors such as 1 and 2. To understand the effect of the ionic media, carbene lifetimes determined in RTIL will be compared with known lifetimes obtained in conventional organic solvents.