Stereoselective synthesis of epoxyisoprostanes: an organocatalytic and "pot-economy" approach.

An efficient and direct synthetic route to epoxyisoprostane EC methyl ester has been accomplished in 8 steps (10% overall yield) from readily available starting materials using a series of asymmetric organocatalytic reactions and one-pot operations.

An epoxyisoprostane is a major regulator of endothelial cell function.

The goal of these studies was to determine the effect of 5,6-epoxyisoprostane, EI, on human aortic endothelial cells (HAEC). EI can form as a phospholipase product of 1-palmitoyl-2-(5,6-epoxyisoprostane E2)-sn-glycero-3-phosphocholine, PEIPC, a proinflammatory molecule that accumulates in sites of inflammation where phospholipases are also increased. To determine the effect of EI on HAEC, we synthesized several stereoisomers of EI using a convergent approach from the individual optically pure building blocks, the epoxyaldehydes 5 and 6 and the bromoenones 14 and 16. The desired stereoisomer of EI can be prepared from these materials in only six operations, and thus, large amounts of the product can be obtained. The trans/trans isomers had the most potent activity, suggesting specificity in the interaction of EI with the cell surface. EI has potent anti-inflammatory effects in HAEC. EI strongly inhibits the production of MCP-1, a major monocyte chemotactic factor, and either decreases or minimally increases the levels of 10 proinflammatory molecules increased by PEIPC. EI also strongly down-regulates the inflammatory effects of IL-1ß, a major inflammatory cytokine. Thus EI, a hydrolytic product of PEIPC, has potent anti-inflammatory function.

Toward the elucidation of the metabolism of 15-E(2)-isoprostane: the total synthesis of the methyl ester of a potential central metabolite.

An 11-step total synthesis of the methyl ester of a potential metabolite of the autoxidatively formed natural product 15-E(2)-IsoP, whose metabolism is not known, is reported. Several vinylogous Mukaiyama aldol additions were tested for the assembly of the acyclic C7-C20 precursor. A new oxidative dianion cyclization served to access the cyclopentane core. The full carbon skeleton was synthesized by an acetylide alkylation. The overall yield of the metabolite amounts to 1.4% for the most efficient route. The results demonstrate convincingly that E(2)-IsoP metabolites are highly epimerization-sensitive and that they may thus also contribute to PGE(2)-action and metabolism.

Total synthesis of 15-D(2t)- and 15-epi-15-E(2t)-isoprostanes.

The first total synthesis of 15-D(2t)-isoprostane is described. (-)-(9S,15S)-15-D(2t)-IsoP 1 and (+)-(11R,15R)-15-epi-15-E(2t)-IsoP 2 have been obtained in 15 steps from orthogonally protected enantiopure bicycle 3. Key features include an easy introduction of the cis side chains via ozonolysis, a highly selective enzymatic chemical differentiation of a non-meso-1,5-diol, and the use of a common synthetic intermediate allowing a stereodivergent approach to the target molecules.

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.

Eicosapentaenoic-acid-derived isoprostanes: synthesis and discovery of two major isoprostanes.

The stereospecific synthesis of two all-syn-EPA-derived isoprostanes (iPs), 5-epi-8,12-iso-iPF(3alpha)-VI 17 and 8,12-iso-iPF(3alpha)-VI 18, has been accomplished. These two synthetic probes have been used to discover and identify their presence in human urine. The eventual quantitative measurement of these two iPs may be a valuable index of oxidative stress in people with eicosapentaenoic acid- (EPA) and docosahexaenoic acid- (DHA) enriched phospholipids.

Improved synthesis of the epoxy isoprostane phospholipid PEIPC and its reactivity with amines.

An improved synthesis of the naturally occurring hydroxy ketone 1-palmitoyl-2-(5,6)-epoxyisoprostane E 2- sn-glycero-3-phosphocholine (PEIPC) 1, a compound that plays a role in endothelial activation in atherosclerosis, has been carried out using a PMB ether as the key protecting group. Opening of an intermediate with pentylamine shows that the allylic epoxide is the position of attack by nucleophiles.

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.

Total Synthesis of the Four Enantiomerically Pure Diasteroisomers of the Phytoprostanes E1Type II and of the 15-E2t-Isoprostanes.

Syntheses of the four enantiomerically pure diastereoisomers of the phytoprostanes E1 type II and 15-E2t-isoprostanes (1-4) are described. The key steps included the preparation of the Freïmanis (+/-)-hydroxycyclopentenone 5, enzymatic resolution of this racemic hydroxycyclopentenone, Wittig and Horner-Wadsworth-Emmons (HWE) coupling reactions and finally enantioselective reductions.

A potential route to neuroprostanes and isoprostanes: preparation of the four enantiomerically pure diastereomers of 13-F4t-neuroP.

We report a potential synthetic route to the isoprostanes and the neuroprostanes that could allow ready access to each of the enantiomerically pure diastereomers of the several regioisomers of these important human metabolites. The key transformation in the synthesis is a highly diastereoselective thermal intramolecular ene reaction. A critical observation is that the four enantiomerically pure diastereomers of an intermediate acetylenic ester are easily separated from one another. Each of these four has been carried on to a different enantiomerically pure diastereomer of 13-F4t-neuroprostane.

E-Ring Isoprostanes Stimulate a Cl Conductance in Airway Epithelium via Prostaglandin E2-Selective Prostanoid Receptors.

Isoprostanes comprise a class of membrane lipid metabolites produced during oxidative stress, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis. They are widely recognized to evoke a variety of biological responses in airway and pulmonary vascular smooth muscle, lymphatics, and innervation. However, their effects on airway epithelium are largely unstudied. We examined the electrophysiological responses evoked by several different isoprostane species in bovine airway epithelium using the Ussing chamber technique. The E-ring isoprostanes 15-E(1t)-IsoP and 15-E(2t)-IsoP evoked a substantial increase in short-circuit current (I(SC)), whereas four different F-ring isomers were ineffective. 15-E(2t)-IsoP-evoked I(SC) was mimicked by the prostaglandin E(2)-selective prostanoid receptor (EP)-agonist prostaglandin E(2) but not by agonists of EP(1)/EP(3)-, FP-, or TP receptors (sulprostone, fluprostenol, and U46619, respectively). This response was significantly reduced by the EP(4)-receptor blocker GW627386 but not by blockers of other prostanoid receptors (ICI 192,605 [TP-selective], SC19220 [EP(1)-selective], AH6809 [DP/EP(1)/EP(2)-selective], and AL8810 [FP-selective]). 15-E(2t)-IsoP-evoked I(SC) was reduced by blockers of Cl(-) channels (niflumic acid and 5-nitro-2-(3-phenylpropylamino)-benzoic acid), of Na(+)/K(+)/2Cl(-) co-transport (furosemide and bumetanide), of adenylate cyclase (MDL 12,330A), or of guanylate cyclase (1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one) but not by blockers of Na(+) conductances (amiloride). We conclude that 15-E(2t)-IsoP activates a transepithelial Cl(-) conductance in bovine airway epithelium through an EP(4) receptor coupled to adenylate cyclase and soluble guanylate cyclase.

General strategy for the synthesis of B1 phytoprostanes, dinor isoprostanes, and analogs.

The synthesis of the phytoprostane B1 types I and II is achieved in high overall yield (35-53%) by only two principal transformations starting from 1,3-cyclopentanedione. The first side chain is attached via O-acylation of the 1,3-dione followed by rearrangement and reduction to give the 2-alkyl-1,3-diones 4a-c. After conversion into the corresponding vinylic iodides 5a-c, the second side chain is introduced by transition metal catalysis following Heck- or Sonogashira-type protocols. The whole spectrum of the phytoprostane B1 types I, II, and the dinor isoprostane B1 type III and some structural analogs are rapidly accessible along the same general protocol.

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.

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.

Total synthesis of the epoxy isoprostane phospholipids PEIPC and PECPC.

A total synthesis of the naturally occurring hydroxy ketone PEIPC 1, a compound that plays a role in endothelial activation in atherosclerosis, has been completed via a triply convergent preparation of a protected EI derivative 13 from 3,5-diacetoxycyclopentene 7, pentane-1,5-diol, and vinyllithium, using Sharpless epoxidation and enzymatic resolution as key steps. Final coupling with lyso-PC 16 and silyl group deprotection gave PECPC 2 and PEIPC 1, which showed the same activity as natural PECPC and PEIPC. [reaction: see text]

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.

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.