Seong-Woo Hwang

Nomenclature of isoprostanes: a proposal.

We have proposed a nomenclature system for the isoprostanes, a new class of natural products formed in vivo by the free-radical peroxidation of polyunsaturated fatty acids. Our proposed nomenclature is based on the assignment of four isoprostanes, 1, 9, 17, and 25, as representatives of the four classes of isoprostanes derived from arachidonic acid (AA). We have attempted as much as possible to retain elements from the familiar prostaglandin nomenclature. In this proposal, we have used the abbreviation i.p. for isoprostane. We have classified isoprostane classes or types based on omega-carbon as being the starting reference. Roman numerals I-VI refer the six types of isoprostanes derived from eicosapentaenoic acid (EPA) and III-VI refer to the four types derived from AA. This nomenclature can be applied to isoprostanes derived from other PUFAs also.

The Isoprostanes: A Perspective

The isoprostanes are a new class of natural products produced in vivo by a non-enzymatic free-radical-induced peroxidation of polyunsaturated fatty acid. In the case of arachidonic acid, for example, four classes of isoprostanes can be produced. Because of the specific structural features distinguishing them from other free-radical-generated products, e.g., HETEs, etc., the isoprostanes can provide an exclusive and selective index for the oxidant component of several inflammatory and degenerative diseases. The possible mechanisms of formation of the individual isoprostanes is discussed in detail. Class III products, such as 8-iso-PGF2 alpha and 8-iso-PGE2 have been shown to be vasoconstrictors and modulate platelet function. Several synthetic representatives from the four classes of arachidonic-acid-derived isoprostanes have already been prepared by total synthesis. These synthetic standards have been used for the identification and quantitation of these isoprostanes in biological fluids using gas chromatography/mass spectrometry methodology.

IDENTIFICATION OF TWO MAJOR F2 ISOPROSTANES, 8,12-ISO- AND 5-EPI-8,12-ISO-ISOPROSTANE F2ALPHA -VI, IN HUMAN URINE

Isoprostanes (iPs) are nonenzymatic, free radical-derived compounds isomeric with enzymatically formed eicosanoids such as prostaglandins, leukotrienes, and thromboxanes. One group formed by the auto-oxidation of arachidonic acid, the F2-iPs, consists of four classes of isomers of prostaglandin F2α (PGF2α). They are relatively abundant in human urine. This fact, along with their chemical stability and excellent characteristics for quantitation by gas chromatography/mass spectrometry, has made them attractive indices of oxidative stress in humans. We developed a specific assay using gas chromatography/mass spectrometry for the first identified F2-iP, iPF2α-III (previously called 8-iso-PGF2α or 8-epi-PGF2α), which demonstrated the utility of monitoring a specific isomer. Recently, we described an assay for another isomer, iPF2α-VI, which is present in urine in greater concentration than iPF2α-III and which is particularly amenable to quantitation. We now describe the identification in human urine of two more isomers, 8,12-iso-iPF2α-VI and 5-epi-8,12-iso-iPF2α-VI, using high performance liquid chromatography/tandem mass spectrometry and gas chromatography/mass spectrometry. These compounds are each present in ∼5-fold greater concentrations than iPF2α-VI (∼20-fold greater than iPF2α-III). They share the unique chemical characteristics of class VI compounds, which make them attractive targets for quantitation by gas chromatography/mass spectrometry and immunoassay development.

Discovery of a Small Molecule Tat-trans-Activation-responsive RNA Antagonist That Potently Inhibits Human Immunodeficiency Virus-1 Replication

Antiretroviral therapy to treat AIDS uses molecules that target the reverse transcriptase and protease enzymes of human immunodeficiency virus, type 1 (HIV-1). A major problem associated with these treatments, however, is the emergence of drug-resistant strains. Thus, there is a compelling need to find drugs against other viral targets. One such target is the interaction between Tat, an HIV-1 regulatory protein essential for viral replication, and trans-activation-responsive (TAR) RNA. Here we describe the design and synthesis of an encoded combinatorial library containing 39,304 unnatural small molecules. Using a rapid high through-put screening technology, we identified 59 compounds. Structure-activity relationship studies led to the synthesis of 19 compounds that bind TAR RNA with high affinities. In the presence of a representative Tat-TAR inhibitor (5 μm TR87), we observed potent and sustained suppression of HIV replication in cultured cells over 24 days. The same concentration of this inhibitor did not exhibit any toxicity in cell cultures or in mice. TR87 was also shown to specifically disrupt Tat-TAR binding in vitro and inhibit Tat-mediated transcriptional activation in vitro and in vivo, providing a strong correlation between its activities and inhibition of HIV-1 replication. These results provide a structural scaffold for further development of new drugs, alone or in combination with other drugs, for treatment of HIV-1-infected individuals. Our results also suggest a general strategy for discovering pharmacophores targeting RNA structures that are essential in progression of other infectious, inflammatory, and genetic diseases.

Total synthesis of a novel isoprostane IPF2α-I and its identification in biological fluids

The first total synthesis of IPF2α-I 25 is described using D-glucose as starting material. This novel isoprostane has been used to establish its presence in human urine.

Total synthesis of 12-epi-PGF2α

Abstract A novel synthesis of 12- epi -PGF 2α 5 is described. The key synthon 11 , which has been used as a starting point for the synthesis, is produced by a radical cyclization process using thionocarbonate 9a . The radical cyclization of 9a to 11 has been studied in some detail.

First total synthesis of isoprostane IPF2α-III

Abstract The first total synthesis of IPF 2α -III, a type III isoprostane is described using a syn-anti-syn lactone 34 prepared from D-glucose and a novel iodohydrin synthon 30 . This is first synthesis of a representative of type III isoprostane which is anticipated to be formed in vivo from arachidonic acid by free-radical mechanism. This synthetic material will help elucidate the formation in vivo of type III isoprostanes.