The biological role of selenium is a subject of intense current interest, and the antioxidant activity of selenoenzymes is now known to be dependent upon redox cycling of selenium within their active sites. Exogenously supplied or metabolically generated organoselenium compounds, capable of propagating a selenium redox cycle, might therefore supplement natural cellular defenses against the oxidizing agents generated during metabolism. We now report evidence that selenium redox cycling can enhance the protective effects of organoselenium compounds against oxidant-induced DNA damage. Phenylaminoethyl selenides were found to protect plasmid DNA from peroxynitrite-mediated damage by scavenging this powerful cellular oxidant and forming phenylaminoethyl selenoxides as the sole selenium-containing products. The redox properties of these organoselenoxide compounds were investigated, and the first redox potentials of selenoxides in the literature are reported here. Rate constants were determined for the reactions of the selenoxides with cellular reductants such as glutathione (GSH). These kinetic data were then used in a MatLab simulation, which showed the feasibility of selenium redox cycling by GSH in the presence of the cellular oxidant, peroxynitrite. Experiments were then carried out in which peroxynitrite-mediated plasmid DNA nick formation in the presence or absence of organoselenium compounds and GSH was monitored. The results demonstrate that GSH-mediated redox cycling of selenium enhances the protective effects of phenylaminoethyl selenides against peroxynitrite-induced DNA damage.

Iso-coenzyme A is an isomer of coenzyme A in which the monophosphate is attached to the 2-carbon of the ribose ring. Although iso-CoA was first reported in 1959 (Moffatt, J. G., and Khorana, H. G. (1959) J. Am. Chem. Soc. 81, 1265-1265) to be a by-product of the chemical synthesis of CoA, relatively little attention has been focused on iso-CoA or on acyl-iso-CoA compounds in the literature. We now report structural characterizations of iso-CoA, acetyl-iso-CoA, acetoacetyl-iso-CoA, and ␤-hydroxybutyryl-iso-CoA using mass spectrometry (MS), tandem MS, and homonuclear and heteronuclear NMR analyses. Although the 2-phosphate isomer of malonyl-CoA was recently identified in commercial samples, previous characterizations of iso-CoA itself have been based on chromatographic analyses, which ultimately rest on comparisons with the degradation products of CoA and NADPH or have been based on assumptions regarding enzyme specificity. We describe a high performance liquid chromatography methodology for separating the isomers of several CoA-containing compounds. We also report here the first examples of isoCoA-containing compounds acting as substrates in enzymatic acyl transfer reactions. Finally, we describe a simple synthesis of iso-CoA from CoA, which utilizes ␤-cyclodextrin to produce iso-CoA with high regioselectivity, and we demonstrate a plausible mechanism that accounts for the existence of iso-CoA isomers in commercial preparations of CoA-containing compounds. We anticipate that these results will provide methodology and impetus for investigating iso-CoA compounds as potential pseudo-substrates or inhibitors of the >350 known CoA-utilizing enzymes.Iso-coenzyme A is an isomer of coenzyme A in which the monophosphate is attached to the 2Ј-carbon of the ribose ring. Iso-CoA was first reported in 1959 by Moffatt and Khorana (1, 2) to be a by-product of the chemical synthesis of CoA. The final step of this synthesis entailed acid-catalyzed hydrolysis of cyclic coenzyme A (Scheme 1) to produce a 50:50 mixture of two products that were separated using epicholorohydrin triethanolamine (ECTEOLA) cellulose ion exchange chromatography (1, 2). Direct structural analysis was not readily available in 1959; consequently, the authors deduced the structure of isoCoA by establishing that, in contrast to CoA, iso-CoA was not a substrate for the enzyme phosphotransacetylase (1, 2). Moffatt and Khorana also used paper chromatography of phosphodiesterase hydrolysates to show that enzymatic hydrolysis of isoCoA produces adenosine-2Ј,5Ј-diphosphate, exclusively (1, 2). Since the original work of Moffatt and Khorana was done, four additional chemical syntheses of CoA have been reported (3-8), all of which produce cyclic CoA as the penultimate product; cyclic CoA is then hydrolyzed either chemically to produce a mixture of CoA and iso-CoA (1, 2, 4 -6, 8) or enzymatically with ribonuclease T2 to produce CoA regioselectively (3-7).Recently, Minkler et al. (9) observed the 2Ј-phosphate isomer of malonyl-CoA in commercial samples. These authors ...

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A series of m-terphenyl amines was synthesized and evaluated as a novel class of cyclooxygenase (COX) inhibitors. Structure-activity relationships (SAR) were investigated by functional group modification at the para-position of the C-1 0 and C-2 0 phenyl substituents on the central aromatic ring. Anilines 6a, b, d, and h demonstrated nonselective inhibition of COX-1 and -2 in human whole blood. Compounds 6c and e demonstrated preferential inhibition of the COX-2 isozyme at 10 lM. Molecules 6f, i, and j inhibited only COX-1, and the disubstituted ethoxy derivative (6g) was inactive as a COX inhibitor ( 100 lM). Molecular docking studies of these compounds indicate that the COX-1 binding site amino acid Ile 523 anchors the m-terphenyl system statically within the enzyme's active site, while the slightly smaller amino acid Val 523 in COX-2 allows the ligand to ''roll,'' fashioning several acceptable conformers.