Stereodivergent synthesis of all 15-F(2) isoprostanes

First Total Synthesis of Phytoprostanes with Prostaglandin-Like Configuration, Evidence for Their Formation in Edible Vegetable Oils and Orienting Study of Their Biological Activity

Phytoprostanes (PhytoP) are natural products, which form in plants under oxidative stress conditions from α-linolenic acid. However, their epimers with relative prostaglandin configuration termed phytoglandins (PhytoG) have never been detected in Nature, likely because of the lack of synthetic reference material. Here, the first asymmetric total synthesis of such compounds, namely of PhytoGF_1α (9-epi-16-F_1t -PhytoP) and its diastereomer ent-16-epi-PhytoGF_1α (ent-9,16-diepi-16-F_1t -PhytoP), has been accomplished. The synthetic strategy is based on radical anion oxidative cyclization, copper(I)-mediated alkyl-alkyl coupling and enantioselective reduction reactions. A UHPLC-MS/MS study using the synthesized compounds as standards indicates PhytoG formation at significant levels during autoxidation of α-linolenic acid in edible vegetable oils. Initial testing of synthetic PhytoGs together with F₁ -PhytoP and 15-F_2t -IsoP derivatives for potential interactions with the PGF_2α (FP) receptor did not reveal significant activity. The notion that PUFA-derived oxidatively formed cyclic metabolites with prostaglandin configuration do not form to a significant extent in biological or food matrices has to be corrected. Strong evidence is provided that oxidatively formed PhytoG metabolites may be ingested with plant-derived food, which necessitates further investigation of their biological profile.

Stereodivergent routes in organic synthesis: marine natural products, lactones, other natural products, heterocycles and unnatural compounds

Enantio- and diastereodivergent routes to marine-origin natural products with different sizes of cyclic ethers and lactones have been used in order to assign stereochemical features. Kainoid amino acids such as isodomoic acids have been synthesized using diastereodivergent routes. The bis(indole) alkaloid dragmacidin F has been prepared by enantiodivergent strategies as well as furanoterpenes and the tetracyclic agelastatin A. Natural products containing five-membered lactones like quercus lactones, muricatacins, goniofufuranones, methylenolactocins and frenolicin B have been synthesized using stereodivergent routes. Macrolides are very abundant lactones and have been mainly prepared from the corresponding seco-acids by lactonization, such as lasiodiplodin, zaeralanes, macrosphelides and haloprins, or by ring-closing metathesis, such as aspercyclides, microcarpalides, macrolides FD-891 and 892, and tetradic-5-en-9-olides. Other natural products including cyclic ethers (such as sesamin, asarinin, acetogenins, centrolobines and nabilones), alcohols (such as sulcatol), esters (such as methyl jasmonates), polycyclic precursors of fredericamycin, amino alcohols (such as ambroxol and sphingosines), isoprostanes, isofurans, polyketide precursors of anachelins, brevicomins, gummiferol, shikimic acid and the related compounds, and the pheromone disparlure have been synthesized stereodivergently. Heterocyclic systems such as epoxides, theobroxides and bromoxones, oxetan-3-ones, 5- to 8-membered cyclic ethers, azetidones, γ-lactams, oxazolidinones, bis(oxazolines), dihydropyridoisoindolines and octahydroisoquinolines have been prepared following stereodivergent routes. Stereodivergent routes to unnatural compounds such as alkenes, dienes, allenes, cyclopropanes, alcohols, aldols, amines, amino alcohols, β-amino acids, carboxylic acids, lactones, nitriles and α-amino nitriles have been considered as well.

UV-Curable Biobased Polyacrylates Based on a Multifunctional Monomer Derived from Furfural

The controlled polymerization of a new biobased monomer, 4-oxocyclopent-2-en-1-yl acrylate (4CPA), was established via reversible addition-fragmentation chain transfer (RAFT) (co)polymerization to yield polymers bearing pendent cyclopentenone units. 4CPA contains two reactive functionalities, namely, a vinyl group and an internal double bond, and is an unsymmetrical monomer. Therefore, competition between the internal double bond and the vinyl group eventually leads to gel formation. With RAFT polymerization, when aiming for a degree of polymerization (DP) of 100, maximum 4CPA conversions of the vinyl group between 19.0 and 45.2% were obtained without gel formation or extensive broadening of the dispersity. When the same conditions were applied in the copolymerization of 4CPA with lauryl acrylate (LA), methyl acrylate (MA), and isobornyl acrylate, 4CPA conversions of the vinyl group between 63 and 95% were reached. The additional functionality of 4CPA in copolymers was demonstrated by model studies with 4-oxocyclopent-2-en-1-yl acetate (1), which readily dimerized under UV light via [2 + 2] photocyclodimerization. First-principles quantum mechanical simulations supported the experimental observations made in NMR. Based on the calculated energetics and chemical shifts, a mixture of head-to-head and head-to-tail dimers of (1) were identified. Using the dimerization mechanism, solvent-cast LA and MA copolymers containing 30 mol % 4CPA were cross-linked under UV light to obtain thin films. The cross-linked films were characterized by dynamic scanning calorimetry, dynamic mechanical analysis, IR, and swelling experiments. This is the first case where 4CPA is described as a monomer for functional biobased polymers that can undergo additional UV curing via photodimerization.

Isoprostanes, neuroprostanes and phytoprostanes: An overview of 25years of research in chemistry and biology

Since the beginning of the 1990's diverse types of metabolites originating from polyunsaturated fatty acids, formed under autooxidative conditions were discovered. Known as prostaglandin isomers (or isoprostanoids) originating from arachidonic acid, neuroprostanes from docosahexaenoic acid, and phytoprostanes from α-linolenic acid proved to be prevalent in biology. The syntheses of these compounds by organic chemists and the development of sophisticated mass spectrometry methods has boosted our understanding of the isoprostanoid biology. In recent years, it has become accepted that these molecules not only serve as markers of oxidative damage but also exhibit a wide range of bioactivities. In addition, isoprostanoids have emerged as indicators of oxidative stress in humans and their environment. This review explores in detail the isoprostanoid chemistry and biology that has been achieved in the past three decades.

Stereodivergent and enantioselective total syntheses of isochaetominines A–C and four pairs of isochaetominine C enantiomers: a six-step approach

We report the first total syntheses of (−)-isochaetominines A–C and eight 2,3-cis-stereoisomers of isochaetominine C, and structural revisions of (−)-pseudofischerine and (−)-aniquinazoline D.

Novel tail and head group prostamide probes

We report the design and synthesis of novel prostaglandin-ethanolamide (PGE2-EA) analogs containing head and tail group modifications to aid in the characterization of a putative prostamide receptor(s). Our synthetic approach utilizes Horner-Wadsworth-Emmons and Wittig reactions to construct the head and the tail moieties of the key PGE2 precursor, which leads to the final products through a peptide coupling, Swern oxidation and HF/pyridine assisted desilylation. The synthesized analogs were shown not to interact significantly with endocannabinoid proteins and recombinant EP1, EP3 and EP4 receptors and suggest a yet to be identified prostamide receptor as their site(s) of action.

Catalytic, enantioselective synthesis of 1,2-anti-diols by asymmetric ring-opening/cross-metathesis

An enantioselective method for the synthesis of 1,2-anti-diols has been developed. A cyclometalated chiral-at-ruthenium complex catalyzes the asymmetric ring-opening/cross-metathesis of dioxygenated cyclobutenes, thus resulting in functionally rich synthetic building blocks. Syntheses of the insect pheromone (+)-endo-brevicomin and monosaccharide ribose demonstrate the synthetic utility of the 1,2-anti-diol fragments generated in the title reaction.

Modular enantioselective synthesis of 8-aza-prostaglandin E1

We report herein for the first time the enantioselective synthesis of 8-aza-PGE1. The synthesis used the cross olefin metathesis reaction to connect the 5-vinyl-γ-lactam subunit, prepared from (R)-malic acid via the Ley's sulfone-based α-amidalkylation protocol (dr = 6.8:1), with the chiral pre-ω-chain. The latter was synthesized in high enantioselectivity from (E)-2-octenol by the Sharpless asymmetric epoxidation and the titanocene-mediated epoxide opening. This modular approach is quite concise and flexible, and requires only eight steps from commercially available reagents.

Isoprostanes and 4-hydroxy-2-nonenal: markers or mediators of disease? Focus on Rett syndrome as a model of autism spectrum disorder

Lipid peroxidation, a process known to induce oxidative damage to key cellular components, has been implicated in several diseases. Following three decades of explorations mainly on in vitro models reproducible in the laboratories, lipid peroxidation has become increasingly relevant for the interpretation of a wide range of pathophysiological mechanisms in the clinical setting. This cumulative effort has led to the identification of several lipid peroxidation end-products meeting the needs of the in vivo evaluation. Among these different molecules, isoprostanes and 4-hydroxy-2-nonenal protein adducts appear to be particularly interesting. This review shows how specific oxidation products, deriving from polyunsaturated fatty acids precursors, are strictly related to the clinical manifestations and the natural history of Rett syndrome, a genetically determined neurodevelopmental pathology, currently classified among the autism spectrum disorders. In our experience, Rett syndrome offers a unique setting for physicians, biologists, and chemists to explore the borders of the lipid mediators concept.

1,3-allylic strain as a strategic diversification element for constructing libraries of substituted 2-arylpiperidines

Flipping diversity

Minimization of 1,3-allylic strain is a recurring element in the design of a stereochemically- and spatially-diverse collection of 2-arylpiperidines. Here, stereochemically-diverse scaffolding is first constructed using A1,3 strain to guide the regioselective addition of nucleophiles, which serve as handles for further substitution. N -substitution with alkyl and acyl substituents again leverages A1,3 strain to direct each stereoisomer to two different conformer populations, doubling the number of library members.

A new approach to the synthesis of polyunsaturated deuterated isoprostanes: total synthesis of d4-5-epi-8,12-iso-iPF3alpha-VI and d4-8,12-iso-iPF3alpha-VI

The total and stereospecific synthesis of d(4)-5-epi-8,12-iso-iPF(3alpha)-VI 55 and d(4)-8,12-iso-iPF(3alpha)-VI 64, EPA-derived all-syn-isoprostanes (iPs), has been accomplished. Because of issues related to volatility and yield with some of the primary deuterated synthons an improved synthesis is presented. These two deuterated analogs were used to discover and quantify the presence of the corresponding endogenous isoprostanes in human urine. These assays may serve as a valuable index of oxidative stress in population with omega-3 fatty acid enriched diets containing eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and may also be useful as an index of the severity of inflammatory diseases such as atherosclerosis and Alzheimer's disease.

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.

A cross-metathesis route to the 5-F(2)-isoprostanes

A library of eight 5-F(2)-isoprostanes was prepared through a ring-opening metathesis/cross-metathesis protocol between functionalized bicyclo[3.2.0]heptenes, ethylene, and alpha,beta-unsaturated ketones. This sequence provided racemic enones in a regio- and stereoselective fashion that could be converted to enantiomerically enriched allylic alcohols through a catalyst-controlled asymmetric reduction. Completion of the sidechains, followed by global deprotection, resulted in a stereodivergent route to eight enantiomerically enriched 5-F(2)-isoprostanes. Overall, the synthesis of this library of known and anticipated lipid oxidation metabolites was achieved in 10 steps from commercially available 4-hydroxy-2-cyclopentenone.

Lactol-directed osmylation. Stereodivergent synthesis of four C-19,20 apoptolidin diols from a single allylic hemiacetal

A synthetic approach to prepare four Apoptolidin C-19,20 diastereomeric diol derivatives was developed. Two diastereomers were obtained from the (Z)-form, which is converted to the (E)-form, followed by dihydroxylation to deliver two more diastereomers. The (E)-allylic hemiacetal and methoxyacetal showed opposite diastereoselectivity.

Cross metathesis as a general strategy for the synthesis of prostacyclin and prostaglandin analogues

[reaction: see text] A cross metathesis (CM) approach has been successfully applied to introduce fully functionalized omega-side chain appendages of various prostacyclin and prostaglandin analogues, resulting in high (E)-selectivities for the C13-C14 double bond and leading to the total syntheses of isocarbacyclin, 15R-TIC, carbacyclin, and PGF(2)(alpha) and the formal syntheses of 15-deoxy-TIC and PGJ(2).

Total synthesis of 8,12-iso-iPF3alpha-VI, an EPA-derived isoprostane: stereoselective introduction of the fifth asymmetric center

[reaction: see text] A new and stereoselective approach for the synthesis of all-syn isoprostanes is reported. This method, which is based on acid-catalyzed Diels-Alder reaction, allows the introduction of the side chain with a predetermined stereochemistry of the hydroxy group. The first total synthesis of an eicosapentaenoic acid (EPA)-derived iP, 8,12-iso-iPF3alpha-VI 10, was performed using this approach.

Synthesis of Isoprostanyl Phosphatidylcholine and Isoprostanyl Phosphatidylethanolamine

The syntheses of two isoprostanyl phospholipids are described. A newly established route to 15-F(2t)-isoprostane and ent-15-epi-F(2t)-isoprostane has allowed for the selective preparation of 15-F(2t)-isoprostanyl phosphatidylethanolamine and ent-15-epi-F(2t)-isoprostanyl phosphatidylcholine. The nature of the headgroups dictates the coupling strategy used to attach the appropriately protected isoprostanes to the corresponding lysophospholipids. Preliminary 1H NMR and 31P NMR studies indicate that these isoprostanyl phospholipids aggregate in apolar solvents.

Exploration of ω-side chain addition strategies for the syntheses of isocarbacyclin and 15R-16-(m-tolyl)-17,18,19,20-tetranorisocarbacyclin

We describe alternative access to prostacyclin analogues by means of two omega-side chain addition strategies: Grignard reagent addition to an alpha,beta-unsaturated Weinreb amide, followed by diastereoselective reduction of the corresponding enone system, and implementation of Seebach's alkylation chemistry. These strategies have led to the syntheses of biologically active prostacyclin analogues isocarbacyclin and 15R- 16-(m-tolyl)- 17,18,19,20-tetranorisocarbacyclin (15R-TIC), with modest to excellent diastereoselectivity.

Les isoprostanes, biomarqueurs de peroxydation lipidique chez l'homme. Partie 1. Nomenclature et synthèse

The synthesis of prostaglandins has been a subject of chemical attractiveness for the last 40 years with the successful strategy developed by Corey et al. via a formyl-lactone in the trans-PG series, derived from the action of cyclooxygenases (COXs). The non-enzymatic metabolic scheme of arachidonic acid, as a free radical catalyzed mechanism, has introduced new data concerning the reactivity of the arachidonyl radical in the absence of COXs and also a growing interest in the total synthesis of isoprostanes and analogues. The potent biological activity of these compounds has been attracting intense research interest since they were detected in humans as well as animal models in the early 1990s. The measurement of these isoprostanes has been regarded as one of the most useful non-invasive biomarkers for oxidative stress status. Two mechanisms for their biosynthesis have been proposed. In the first mechanism, a peroxyl radical undergoes successive 5-exo cyclizations analogous to the enzymatic mechanism proposed for prostaglandin biosynthesis. The second mechanism starts with a 4-exo cyclization of a peroxyl radical leading to an intermediate dioxetane. During the last two decades, several approaches towards the synthesis of isoprostanes and analogues have been reported in the literature by several groups of chemists. Finally, to date, two nomenclatures have been proposed by Taber et al. and Rokach et al., but only Taber's nomenclature have been approved by IUPAC.

Total synthesis of isoprostanes: discovery and quantitation in biological systems

Isoprostanes (iP's), a new class of natural products isomeric with prostaglandins, are formed as the result of free radical oxygenation of polyunsaturated fatty acids. We have identified these iP's and developed analytical methodology to measure them in biological fluids. The approach we took, which led to the discovery and measurement of iP's, is as follows: (1) based on some biochemical and chemical considerations, we proposed possible structures for these isoprostanes; (2) we performed the total syntheses of some of these iP's, in particular Groups III through VI, and used them as markers for their discovery in biological fluids and developed a GC/MS and an LC/MS methodologies based on iPF2alpha-III, iPF2alpha-VI, and 8,12-iso-iPF2alpha-VI; (3) with the help of these assays, we measured elevated levels of iP's in Alzheimer's disease and atherosclerosis.

The diazo ketone approach to the isoprostanes

A general synthetic approach to the isoprostanes has been established, based on intermolecular aldol condensation of a diazo ketone with an unsaturated aldehyde, followed by cyclization of the resulting diazo ketone to the cyclopropane. Subsequent kinetic opening with thiophenol followed by further elaboration then leads to the isoprostane. The history of this approach and the details of its development are discussed.

Total syntheses of iso-, neuro- and phytoprostanes: new insight in lipid chemistry

Isoprostanes (IsoPs) are a complex family of compounds produced, in vivo, from peroxidation of polyunsaturated fatty acids (AA, DHA, EPA, alpha-linolenic) via a free-radical-catalyzed mechanism. Carbocyclic annulations are extremely important reactions and the stereocontrolled intramolecular free-radical cyclization has emerged as a powerful tool for carbon-carbon bond formation in synthetic chemistry. The hex-5-enyl radical cyclization is the most well-known for the synthesis of cyclopentane rings. After a short review of the literature, concerning the total synthesis of isoprostanes and intermediates, we will present our own contributions on the preparation of chiral cyclopentane rings from glucose leading to new isoprostanes. This study allowed us to control the cyclization outcome to yield the all-syn and/or syn-anti-syn precursors which permit us to the total synthesis of a large set of iso-, neuro-, and phytoprostanes.

Recent advances in the stereoselective synthesis of isoprostanes and neuroprostanes

This review delineates several reported methods for the synthesis of isoprostanes and neuroprostanes with particular emphasis on the stereocontrolled construction of a suitably functionalized cyclopentane core. The alpha- and omega-side chains of these PG-like molecules are typically assembled by Wittig-type olefination reactions, standard transformations in the PG synthesis. The synthetic strategies include free radical cyclizations, a palladium-promoted coupling of three different components, an intramolecular cyclopropanation reaction-ring-opening sequence, a [2+2] photocycloaddition-ring-opening metathesis approach, and an intramolecular cross-coupling reaction of an alkyl iodide and a tethered alkenylsiloxane.

Synthesis of the eight enantiomerically pure diastereomers of the 12-F(2)-isoprostanes

Syntheses of the eight enantiomerically pure diastereomers of the 12-F(2)-isoprostanes (4-11) are described. The key steps included rhodium-mediated intramolecular cyclopropanation and enzymatic resolution of the racemic diol 12.