A cautionary note on the correct structure assignment of phytoprostanes and the emergence of a new prostane ring system

Considerable confusion exists about the correct structural representation of phytoprostanes (PhytoP). Improper use of the different nomenclature systems leads to incorrect structure assignment of PhytoP, which results in wrong synthetic approaches to these molecules and may lead to wrong rationalization of biological activity. A new prostane ring system was found, which is proposed to be termed L(1)-PhytoP or L(2)-IsoP, respectively.

New bioactive oxylipins formed by non-enzymatic free-radical-catalyzed pathways: the phytoprostanes

In animals and plants, fatty acids with at least three double bonds can be oxidized to prostaglandin-like compounds via enzymatic and non-enzymatic pathways. The most common fatty acid precursor in mammals is arachidonic acid (C20:4) (AA) which can be converted through the cyclooxygenase pathway to a series of prostaglandins (PG). Non-enzymatic cyclization of arachidonate yields a series of isoprostanes (IsoP) which comprises all PG (minor compounds) as well as PG isomers that cannot be formed enzymatically. In contrast, in plants, alpha-linolenic acid (C18:3) (ALA) is the most common substrate for the allene oxide synthase pathway leading to the jasmonate (JA) family of lipid mediators. Non-enzymatic oxidation of linolenate leads to a series of C18-IsoPs termed dinor IsoP or phytoprostanes (PP). PP structurally resemble JA but cannot be formed enzymatically. We will give an overview of the biological activity of the different classes of PP and also discuss their analytical applications and the strategies developed so far for the total synthesis of PP, depending on the synthetic approaches according to the targets and which key steps serve to access the natural products.

Stereocontrolled access to isoprostanes via a bicyclo[3.3.0]octene framework

We report a simple and highly stereocontrolled strategy toward the total synthesis of isoprostanes based on a bicyclic alpha,beta-epoxy ketone intermediate 6. Bicyclo[3.3.0]octene scaffold permitted stereodirection of reagents allowing stereoselective epoxidation, diastereoselective ketone reduction, and regioselective epoxide opening otherwise not accessible with a simple cyclopentene framework.

Beyond prostaglandins--chemistry and biology of cyclic oxygenated metabolites formed by free-radical pathways from polyunsaturated fatty acids

Polyunsaturated fatty acids (PUFAs) are important constituents in all organisms. They fulfil many functions, ranging from modulating the structure of membranes to acting as precursors of physiologically important molecules, such as the prostaglandins, which for a long time were the most prominent cyclic PUFA metabolites. However, since the beginning of the 1990s a large variety of cyclic metabolites have been discovered that form under autoxidative conditions in vivo to a much larger extent than do prostaglandins. These compounds--isoprostanes, neuroprostanes, phytoprostanes, and isofurans--proved subsequently to be ubiquitous in nature. They display a wide range of biological activities, and isoprostanes have become the currently most reliable indicators of oxidative stress in humans. In a relatively short time, the structural variety, properties, and applications of the autoxidatively formed cyclic PUFA derivatives have been uncovered.

Enantioselective access to isoquinuclidines by tropenone desymmetrization and homoallylic radical rearrangement: synthesis of (+)-ibogamine

[reaction: see text]. Chiral lithium amide-induced desymmetrization of a tropenone and subsequent Bu3SnH-catalyzed nitrogen-directed homoallylic radical rearrangement constitute key steps in a new strategy to dehydroisoquinuclidines. The strategy was applied in a synthesis of (+)-ibogamine.

Enantioselective total synthesis of (-)-xialenon A

The first total synthesis of (-)-xialenon A (1) via conjugate allylation of a 1,5-cyclooctadiene-derived bicyclo[3.3.0]octenone 3 and an alpha'-hydroxylation on the more hinderd face of enone 9 using hypervalent iodine chemistry, is described.