Synthesis of a plasmenylethanolamine.

A concise synthesis of a plasmenylethanolamine (PlsEtn-[16:0/18:1 n-9]), known as antioxidative phospholipids commonly found in cell membranes, has been achieved from an optically active known diol through 8 steps. The key transformations for the synthesis of PlsEtn-[16:0/18:1 n-9] are (1) regio- and Z-selective vinyl ether formation via the alkylation of a lithioalkoxy allyl intermediate with an alkyl iodide, and (2) a one-pot phosphite esterification-oxidation sequence to construct the ethanolamine phosphonate moiety in the presence of the vinyl ether functionality. The piperidine salt of synthetic PlsEtn-[16:0/18:1 n-9] was desalinated through reversed-phase high-performance liquid chromatography purification.

Interaction of plasmenylcholine with free radicals in selected model systems.

Plasmalogens (Plg) - naturally occurring glycerophospholipids with the vinyl-ether group in the sn-1 position are generally viewed as physiological antioxidants. Although there are numerous examples of antioxidant action of plasmalogen in cell cultures and in experimental animals, this hypothesis is far from being satisfactorily proven due to substantial limitations of such studies. Thus, plasmalogen reactivity in cells results in the accumulation of toxic byproducts and the experimental design is usually too complicated to evaluate the protective function of solely one type of lipid molecular species. In this study, experiments were performed in homogenous and heterogeneous model systems consisting of solutions in organic solvents as well as micelles and liposomes containing pure synthetic plasmenylcholines. Under the experimental conditions used, chemical reactivity of plasmalogens could be attributed to specific fatty acid esterification pattern. This is important because the chemical reactivity cannot be separated from physico-chemical properties of the lipids. Time-dependent formation of phospholipid and cholesterol hydroperoxides were determined by iodometric assay and HPLC-EC. EPR oximetry and Clark electrode were employed to detect the accompanying changes in oxygen concentration. Oxidation of the studied lipids was monitored by standard colorimetric TBARS method as well as MALDI-TOF mass spectrometry. Our data indicate that the reactivity of sn-2 monounsaturated vinyl ether lipids in peroxyl radical-induced or iron-catalyzed peroxidation reactions is comparable with that of their diacyl analogs. In samples containing cholesterol and plasmalogens, oxidative processes lead to accumulation of the radical oxidation product of cholesterol. It can be concluded that the antioxidant action of plasmalogens takes place intramolecularly rather than intermolecularly and depends on the degree of unsaturation of esterified fatty acids. Thus, it is questionable if plasmalogens can really be viewed as "endogenous antioxidant", even though they may exhibit, under special conditions, protective effect.

Chemical Derivatization and Ultrahigh Resolution and Accurate Mass Spectrometry Strategies for "Shotgun" Lipidome Analysis.

Lipids play critical structural and functional roles in the regulation of cellular homeostasis, and it is increasingly recognized that the disruption of lipid metabolism or signaling or both is associated with the onset and progression of certain metabolically linked diseases. As a result, the field of lipidomics has emerged to comprehensively identify and structurally characterize the diverse range of lipid species within a sample of interest and to quantitatively monitor their abundances under different physiological or pathological conditions. Mass spectrometry (MS) has become a critical enabling platform technology for lipidomic researchers. However, the presence of isobaric (i.e., same nominal mass) and isomeric (i.e., same exact mass) lipids within complex lipid extracts means that MS-based identification and quantification of individual lipid species remains a significant analytical challenge. Ultrahigh resolution and accurate mass spectrometry (UHRAMS) offers a convenient solution to the isobaric mass overlap problem, while a range of chromatographic separation, differential extraction, intrasource separation and selective ionization methods, or tandem mass spectrometry (MS/MS) strategies may be used to address some types of isomeric mass lipid overlaps. Alternatively, chemical derivatization strategies represent a more recent approach for the separation of lipids within complex mixtures, including for isomeric lipids. In this Account, we highlight the key components of a lipidomics workflow developed in our laboratory, whereby certain lipid classes or subclasses, namely, aminophospholipids and O-alk-1'-enyl (i.e., plasmalogen) ether-containing lipids, are shifted in mass following sequential functional group selective chemical derivatization reactions prior to "shotgun" nano-ESI-UHRAMS analysis, "targeted" MS/MS, and automated database searching. This combined derivatization and UHRAMS approach resolves both isobaric mass lipids and certain categories of isomeric mass lipids within crude lipid extracts, with no requirement for extensive sample handling prior to analysis, with additional potential for enhanced ionization efficiencies, improved molecular level structural characterization, and multiplexed relative quantification. When integrated with a monophasic method for the simultaneous global extraction of both highly polar and nonpolar lipids, this workflow has been shown to enable the sum composition level identification and relative quantification of 500-600 individual lipid species across four lipid categories and from 36 lipid classes and subclasses, in only 1-2 min data acquisition time and with minimal sample consumption. Thus, while some analytical challenges remain to be addressed, shotgun lipidomics workflows encompassing chemical derivatization strategies have particular promise for the analysis of samples with limited availability that require rapid and unbiased assessment of global lipid metabolism.

Synthesis and evaluation of immunostimulant plasmalogen lysophosphatidylethanolamine and analogues for natural killer T cells.

Plasmalogen lysophosphatidylethanolamine (pLPE) had been identified as a self antigen for natural killer T cells (NKT cells). It is very important in the development, maturation and activation of NKT cells in thymus. Besides, pLPE is a novel type of antigen for NKT cells. To evaluate the structure-activity relationship (SAR) of this new antigen, pLPE and its analogues referred to different aliphatic chains and linkages at the sn-1 position of the glycerol backbone were synthesized, and the biological activities of these analogues was characterized. It is discovered that the linkages between phosphate and lipid moiety are not important for the antigens' activities. The pLPE analogues 1, 3, 4, 7 and 9, which have additional double bonds on lipid parts, were identified as new NKT agonists. Moreover, the analogues 4, 7 and 9 were discovered as potent Th2 activators for NKT cells.

Neonatal adrenoleukodystrophy: a clinical, pathologic, and biochemical study.

Neonatal adrenoleukodystrophy constitutes a distinct genetic disorder of autosomal recessive inheritance, and is distinguishable from the cerebro-hepato-renal syndrome of Zellweger and X-linked juvenile adrenoleukodystrophy, although all three conditions store very long chain fatty acids. Abnormal clinical features in neonatal adrenoleukodystrophy are generally present at birth, and include muscle hypotonia, severe psychomotor retardation, and failure to thrive. These infants are generally blind and deaf, with seizures developing during their first few weeks. A retinopathic "leopard spot" is common, and should help identify this disorder. The brains of four infants who died of neonatal adrenoleukodystrophy were biochemically analyzed for complex lipids, including cholesterol, cholesterol esters, total phospholipids, total galactolipids, and gangliosides. Additional analyses included the separation and identification of very long chain fatty acids and various forms of brain plasmalogen. Analyses of brains with neonatal adrenoleukodystrophy revealed the chemical identification of at least two stored lipid products. Very long chain fatty acids are present, especially in cholesterol esters, and vinyl ether ethanolamine plasmalogens are markedly elevated. The storage of vinyl ether plasmalogen in brains of infants dying of neonatal adrenoleukodystrophy clearly distinguishes them from those with cerebro-hepato-renal syndrome of Zellweger, which fail to synthesize plasmalogens.

Catalytic Z-selective olefin cross-metathesis for natural product synthesis.

Alkenes are found in many biologically active molecules, and there are a large number of chemical transformations in which alkenes act as the reactants or products (or both) of the reaction. Many alkenes exist as either the E or the higher-energy Z stereoisomer. Catalytic procedures for the stereoselective formation of alkenes are valuable, yet methods enabling the synthesis of 1,2-disubstituted Z alkenes are scarce. Here we report catalytic Z-selective cross-metathesis reactions of terminal enol ethers, which have not been reported previously, and of allylic amides, used until now only in E-selective processes. The corresponding disubstituted alkenes are formed in up to >98% Z selectivity and 97% yield. These transformations, promoted by catalysts that contain the highly abundant and inexpensive metal molybdenum, are amenable to gram-scale operations. Use of reduced pressure is introduced as a simple and effective strategy for achieving high stereoselectivity. The utility of this method is demonstrated by its use in syntheses of an anti-oxidant plasmalogen phospholipid, found in electrically active tissues and implicated in Alzheimer's disease, and the potent immunostimulant KRN7000.

Synthesis and antioxidant properties of an unnatural plasmalogen analogue bearing a trans O-vinyl ether linkage.

To assess the antioxidant behavior of trans-1, we first synthesized trans-allyl ether 4 by opening an (S)-glycidol derivative with an (E)-alk-2-en-ol, and then produced the unnatural E-enol ether 1 by a stereoselective iridium(I)-catalyzed olefin isomerization. Natural cis-1 was preferentially degraded by HOCl and was more protective than trans-1 against lipid peroxidation induced by a free-radical initiator, demonstrating that the geometry of the 1'-alkenyloxy bond participates in the antioxidant defensive role of 1.

Improved plasmalogen synthesis using organobarium intermediates.

An improved synthesis of plasmalogen type lipids is described. Transmetalation of lithioalkoxy allyl intermediates with BaI(2) and subsequent alkylation with 1-iodoalkanes enables the stereoselective formation of O-(Z)-alkenyl ether as precursors for the synthesis of plasmenyl- and bisplasmenylcholines. This method provides a simple and adaptable approach for the stereocontrolled synthesis of plasmenyl derivatives with variations at the sn-1, sn-2, and sn-3 positions of the glycerol backbone.

Direct synthesis of plasmenylcholine from allyl-substituted glycerols.

We report a new method for the facile preparation of plasmenylcholine via reaction of lithioalkoxy allyl intermediates with 1-iodoalkanes as the key step in the stereoselective formation of 1'-(Z)-alkenyl glyceryl ethers. The allyl anion intermediate is prepared by treating mono- or disiloxy-protected 1-allylglycerol precursors with s-BuLi at -65 to -80 degrees C. Subsequent addition of 1-iodoalkane solutions at low temperature gives moderate yields of gamma-coupled, Z-vinyl ethers as the major product and alpha-coupled product as the minor component. Several different preparative strategies for the total synthesis of plasmalogens are enabled by this simple transformation.

Facile synthesis of plasmalogens via Barbier-type reactions of vinyl dioxanes and vinyl dioxolanes with alkyl halides in LiDBB solution.

Plasmalogens (i.e. plasmenylcholines or plasmenylethanolamines) are a biologically important class of glycerophospholipids that have been difficult to synthesize due to the presence of an acid and oxidatively labile (Z)-vinyl ether substituent at the sn-1 position and a base-labile sn-2 acyl substituent that easily migrates during silica gel purification. We report two facile synthetic methods for the preparation of racemic plasmenylcholines via a tandem reductive vinyl dioxane/dioxolane ring opening and alkyliodide coupling process that proceeds in a single pot reaction. The key step in the formation of (Z)-vinyl ether precursors for the production of plasmenylcholines is accomplished using LiDBB under Barbier-type conditions to give the corresponding TBDMS-protected 1-O-Z'-vinylglycerol intermediate in moderate yields. This pathway is the most direct synthetic route for the formation of plasmenylcholines to date, requiring a total of six transformations from acrolein and glycerol or solketal as inexpensive starting materials, to generate glycerophosphocholine-type plasmalogens in 4% overall yield.

Plasmenylethanolamine facilitates rapid membrane fusion: a stopped-flow kinetic investigation correlating the propensity of a major plasma membrane constituent to adopt an HII phase with its ability to promote membrane fusion.

A critical step in membrane fusion involves the formation of a lipid intermediate which shares a conformational similarity with an inverted hexagonal phase (HII). Since plasmenylethanolamines possess a marked propensity for hexagonal phase formation and represent a major lipid constituent of several membrane systems which undergo rapid membrane fusion (e.g., plasma membranes and synaptic vesicle membranes), we compared the relative fusogenicity of lipid vesicles containing plasmenylethanolamine to that of vesicles containing their diacyl phospholipid counterpart (i.e., phosphatidylethanolamine). Vesicles comprised of equimolar mixtures of phosphatidylcholine and phosphatidylethanolamine fused slowly with phosphatidylserine vesicles in the presence of 10 mM CaCl2, as assessed either by lipid mixing (dequenching of octadecyl rhodamine fluorescence, 7.4 Fmax% s-1) or internal contents mixing (fluorescence enhancement from the resultant Tb/dipicolinic acid charge transfer complex, 8.7Fmax% s-1). In stark contrast, vesicles comprised of equimolar mixtures of phosphatidylcholine and plasmenylethanolamine fused three times more rapidly, as assessed by both lipid mixing (22.1 Fmax% s-1) and internal contents mixing (21.4Fmax% s-1) assays. The importance of an HII-like intermediate in membrane fusion was further substantiated by demonstration that plasmenylethanolamines containing arachidonic acid at the sn-2 position (which demonstrate a greater propensity for HII phase formation) exhibited the most rapid rate of membrane fusion (five times greater than phosphatidylethanolamine containing oleic acid at the sn-2 position). Furthermore, vesicles containing plasmenylethanolamines in physiologic ratios with other phospholipids (i.e., PC/PE/PS, 45:45:10, mol/mol) underwent fusion six times more rapidly (4.4Fmax% min-1) than corresponding vesicles in which plasmenylethanolamine was replaced with phosphatidylethanolamine (0.7Fmax% min-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of 1-O-alkyl-, 1-O-alk-1'-enyl-, and 1-O-acyl-2-acetyl-sn-glycero-3-phosphoethanolamines and -3-phosphocholines as agonists of the platelet-activating factor family.

Four naturally occurring platelet-activating factor (PAF) analogs, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphocholine, 1-hexadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, 1-octadecanoyl-2-acetyl-sn-glycero-3-phosphocholine, and 1-alkyl-2-acetyl-sn-glycero-3-phosphoethanolamine, stimulated human neutrophils (PMN) to mobilize Ca2+, degranulate, and produce superoxide anion. They were, respectively, 5-, 300-, 500-, and 4000-fold weaker than PAF in each assay; inhibited PMN-binding of [3H]PAF at concentrations paralleling their biological potencies; and showed sensitivity to the inhibitory effects of PAF antagonists. PAF and the analogs, moreover, desensitized PMN responses to each other but not to leukotriene B4 and actually increased (or primed) PMN responses to N-formyl-MET-LEU-PHE. Finally, 5-hydroxyeicosatetraenoate-enhanced PMN responses to PAF and the analogs without enhancing the actions of other stimuli. It stereospecifically raised each analog's potency by as much as 100-fold and converted a fifth natural analog, 1-alk-1'-enyl-2-acetyl-sn-glycero-3-phosphoethanolamine from inactive to a weak stimulator of PMN. PAF and its analogs thus represent a structurally diverse family of cell-derived phospholipids which can activate, prime, and desensitize neutrophils by using a common, apparently PAF receptor-dependent mechanism.

Semisynthesis and purification of homogeneous plasmenylcholine molecular species.

Methods for the efficient use of limiting amounts of fatty acid probes in the synthesis of individual molecular species of plasmenylcholine have been developed. Plasmenylcholine molecular species were synthesized through acylation of homogeneous 1-O-(Z)-hexadec-1'-enyl-sn-glycero-3-phosphocholine utilizing fatty acid anhydrides generated in situ from combined pools of reactant and recycled fatty acids by repeated addition of small amounts (10 mol%) of N,N'-dicyclohexylcarbodiimide. The efficient generation of reactive anhydrides was accomplished through minimizing irreversible formation of N-acyl urea adducts by maintaining a persistent molar excess of fatty acid (with respect to carbodiimide) during the entire reaction time course. The synthesis of multiple different sn-2 labeled plasmenylcholine probes for utilization in fluorescence, ESR, or 2H NMR spectroscopy as well as isotopically labeled plasmenylcholines for metabolic studies has been achieved in good yield (40-50% of theoretical yield based on fatty acid) by these methods. Rapid and effective purification methods utilizing high-performance liquid chromatography were developed for both large- and small-scale purifications of individual reaction mixtures which collectively resulted in the isolation of homogeneous plasmenylcholine molecular species in high yield from limiting amounts of fatty acid probes.

Disparate molecular dynamics of plasmenylcholine and phosphatidylcholine bilayers.

The molecular dynamics of binary dispersions of plasmenylcholine/cholesterol and phosphatidylcholine/cholesterol were quantified by electron spin resonance (ESR) and deuterium magnetic resonance (2H NMR) spectroscopy. The order parameter of both 5-doxylstearate (5DS) and 16-doxylstearate (16DS) was larger in vesicles comprised of plasmenylcholine in comparison to phosphatidylcholine at all temperatures studied (e.g., S = 0.592 vs. 0.487 for 5DS and 0.107 vs. 0.099 for 16DS, respectively, at 38 degrees C). Similarly, the order parameter of plasmenylcholine vesicles was larger than that of phosphatidylcholine vesicles utilizing either spin-labeled phosphatidylcholine or spin-labeled plasmenylcholine as probes of molecular motion. The ratio of the low-field to the midfield peak height in ESR spectra of 16-doxylstearate containing moieties (i.e., spin-labeled plasmenylcholine and phosphatidylcholine) was lower in plasmenylcholine vesicles (0.93 +/- 0.01) in comparison to phosphatidylcholine vesicles (1.03 +/- 0.01). 2H NMR spectroscopy demonstrated that the order parameter of plasmenylcholine was greater than that of phosphatidylcholine for one of the two diastereotopic deuterons located at the C-2 carbon of the sn-2 fatty acyl chain. The spin-lattice relaxation times for deuterated plasmenylcholine and phosphatidylcholine in binary mixtures containing 0-50 mol % cholesterol varied nonmonotonically as a function of cholesterol concentration and were different for each phospholipid subclass. Taken together, the results indicate that the vinyl ether linkage in the proximal portion of the sn-1 aliphatic chain of plasmenylcholine has substantial effects on the molecular dynamics of membrane bilayers both locally and at sites spatially distant from the covalent alteration.

Endothelium-dependent vasorelaxation induced by Cn-acetal plasmalogens.

In this study the effects of the synthetic acetal plasmalogens (AP) C17-AP, C13-AP, C9-AP on isolated rabbit aorta were investigated with emphasis on their putative relationship with endothelium-dependent relaxing factor (EDRF). The various AP were obtained by total synthesis from the related fatty acid chlorides. In isolated rabbit aorta precontracted with phenylephrine (PE, 10(-7) M), C17-AP (greater than 10(-6) M) and C13-AP (greater than 10(-5) M) exerted an endothelium-dependent relaxation (EDR). In contrast, C9-AP was totally devoid of effect. Given 30 or 45 min before PE, C17-AP (greater than 10(-6) M) and C13-AP (greater than 10(-5) M) abolished the carbachol-induced ERD; moreover, following preincubation with C17-AP, enhanced contraction was obtained with carbachol. Similar effects were obtained with preincubation of aortas with both AA(10(-4) M) and A 23 187 (10(-8) M). Conversely preincubation of aortas with carbachol (3X 10(-6) M) and ATP (3 X 10(-5) M) did not significantly modify the carbachol-induced EDR. Atropine (3 X 10(-7) M) did not affect the relaxation induced by C17-AP and C13-AP. The in vivo effects are correlated with the in vitro actions of acetal plasmalogens: C17-AP and C13-AP but not C9-AP, given iv (5 mg/kg) induced a pronounced but transient hypotension which lasted 2-3 min and which was followed by a persistent hypertensive state. Atropine (0.5 and 1 mg/kg; iv) given 5 min before C17-AP inhibited the secondary hypertensive phase. These results show that C17-AP and C13-AP should be added to the list of compounds capable of releasing EDRF.

Semi-synthetic approach for the preparation of homogeneous plasmenylethanolamine utilizing phospholipase D from Streptomyces chromofuscus.

A simple method for the preparation of homogeneous molecular species of plasmenylcholine and plasmenylethanolamine was developed. The method utilized reverse phase high performance liquid chromatography to isolate homogeneous molecular species of plasmenylcholine prepared by acylation of lysoplasmenylcholine. Plasmenylcholine was directly converted to plasmenylethanolamine by transphosphatidylation utilizing phospholipase D from Streptomyces chromofuscus. This method permits the facile labeling of homogeneous molecular species of plasmalogens in the polar head group, the sn-2 acyl chain, or both, for the first time.