Study of carbohydrate-carbohydrate interactions: total synthesis of 6d-deoxy Lewis pentaosyl glycosphingolipid

This article describes total synthesis of 6d-deoxy Lewis^x pentaosyl glycosphingolipid, a useful tool for study of the Lewis^x-Lewis^x interaction. A 6-deoxy galactose donor was condensed with a diol of glucosamine to provide regioselectively a β 1→4 linked disaccharide, which was further fucosylated to a protected deoxy Lewis^x trisaccharide. Glycosylation of a lactoside diol with the 6d-deoxy Lewis^x trisaccharide gave regio- and stereoselectively a pentasaccharide in excellent yield. After chemical modification, this pentasaccharide reacted with the 3-O-benzoylated azidosphingosine to form a glycosphingolipid, which, after azide reduction followed by condensation with stearic acid and deprotection, afforded the target compound.     

First synthesis of 3′-deoxy Lewisx pentasaccharide

The total synthesis of 3′-deoxy Lewis^x pentasaccharide is reported. 4-O-Acetyl-2,6-di-O-benzoyl-3-deoxy-β-d-xylo-hexopyranosyl trichloroacetimidate was condensed with a diol of glucosamine to give a disaccharide, which was further fucosylated to a Lewis^x trisaccharide analogue. Glycosylation of a lactoside diol with this trisaccharide provided a pentasaccharide, which after deprotection, afforded the target pentasaccharide.     

N-连接的糖蛋白核心甘露五糖及其异构体的合成研究

以1,2-O-亚乙基-4,6-O-亚苄基-β-D-甘露糖(2)和2,3,4,6-四-O-苯甲酰基-α-D-甘露吡喃糖基三氯乙酰亚胺酯(3)为基本原料，经一些简单的化学转换和选择性的糖基化反应，得到了甘露核心五糖及其异构体。     

Synthesis of tri- and pentasaccharide fragments corresponding to the O-antigen of Shigella boydii type 6

A convenient synthetic strategy for the synthesis of the acidic pentasaccharide repeating unit and its trisaccharide fragment corresponding to the O-antigen of Shigella boydii type 6 has been successfully developed. A stereoselective sequential glycosylation method has been exploited to obtain the target tri- and pentasaccharide derivatives. Most of the synthetic intermediates were solid and prepared in high yields from commercially available reducing sugars following a series of protection–deprotection reactions. A late-stage TEMPO mediated selective oxidation reaction finally resulted in the pentasaccharide containing a glucuronic acid unit. A 2-(4-methoxyphenoxy) ethyl group has been chosen as the anomeric protecting group to provide trisaccharide and pentasaccharide derivatives linked to an ethylene glycol linker.     

Total synthesis of sialylated and sulfated oligosaccharide chains from respiratory mucins

The total syntheses of several complex oligosaccharide moieties that occur in the core structure of sulfated mucins are reported. A trisaccharide acceptor was obtained through regio- and stereoselective sialylation of methyl (6-O-pivaloyl-beta-D-galactopyanosyl)(1-->3)-4,6-O-benzylidene-2-a cetamido-2-deoxy-alpha-D-galactopyranoside with a novel sialyl donor. A tetrasaccharide, pentasaccharide, and hexasaccharide were constructed in predictable and controlled manner with high regio- and stereoselectivity after the successful preparation and employment of a disaccharide donor, trisaccharide donor, disaccharide acceptor, and trisaccharide acceptor building blocks. Finally, a mild oxidative cleaving method was adopted for the selective removal of 2-naphthylmethyl (NAP) in the presence of benzyl groups.     

New synthesis of idraparinux,the non-glycosaminoglycan analogue of the antithrombin-binding domain of heparin

Idraparinux, the fully O-sulfated, O-methylated, heparin-related pentasaccharide possessing selective factor Xa inhibitory activity, was prepared by a new synthetic pathway. This route was based on a [2+3] block synthesis utilizing a 6-O-silyl-protected l-idose-containing trisaccharide acceptor, which was glycosylated with a disaccharide donor containing a non-oxidized precursor of the glucuronic acid. The unique strategy of multiple functionalizations at pentasaccharide levels, involving triple methylation followed by oxidation of the glucose and the idose precursors into d-glucuronic and l-iduronic acids in one step, proved to be highly efficient, providing the target pentasaccharide through a 39-step synthesis starting from d-glucose and methyl α-d-glucopyranoside.     

First Total Synthesis of Trehalose‐Containing Branched Oligosaccharide OSE‐1 of Mycobacterium gordonae (Strain 990)

The first total synthesis of the branched oligosaccharide OSE‐1 of Mycobacterium gordonae (strain 990) is reported. An intramolecular aglycon delivery approach was used for constructing the desymmetrized 1,1′‐α,α‐linked trehalose moiety. A [3+2] glycosylation of the trisaccharide donor and trehalose acceptor furnished the right hand side pentasaccharide. Regioselective O3 glycosylation of L ‐rhamnosyl 2,3‐diol allowed expedient synthesis of the left hand side tetrasaccharide. The nonasaccharide was assembled in a highly convergent fashion through a [4+5] glycosylation.     

Convergent synthesis of a common pentasaccharide-repeating unit corresponding to the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12

A convergent chemical synthesis of a pentasaccharide found in the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12 has been achieved in excellent yield. A [3+2] block synthetic strategy has been adopted to couple a disaccharide donor 11 with a trisaccharide acceptor 10 for the construction of the pentasaccharide derivative 12 which on deprotection furnished target pentasaccharide 1 as its 4-methoxyphenyl glycoside. Disaccharide thioglycoside donor 11 and trisaccharide acceptor 10 were prepared from suitably protected monosaccharide intermediates. Yields were excellent in all steps.     

Water Compatible Photoarylation of Amino Acids and Peptides

A novel photoarylation of amino acids and peptides is described, which tolerates the presence of water. Irradiation of Boc‐protected amino acids in the presence of N‐protected 2‐azidobenzimidazoles leads to selective arylation of carboxy termini or side chains. The new reaction also works for peptides. Irradiation of the nonapeptide H‐SPSYVYHQF‐OH also resulted in selective arylation of the tyrosine side chains, as indicated by ESI‐MS/MS fragmentation. Chemo‐ and regioselectivity could add the title reaction to the repertoire of photoaffinity labeling methods.     

Gangliosides from the starfishEvasterias echinosoma: identification of a disialoganglioside containing 8-O-methyl-N-acetylneuraminic acid andN-formylgalactosamine

Gangliosides were isolated from the starfishEvasterias echinosoma and their structures were elucidated by chemical and physicochemical methods. Two major gangliosides were found to be disialogangliosides, whose carbohydrate chain is based on the trisaccharide β-N-acylgalactosaminyl-(l→3)-β-galactosyl-(l→4)-β-glucose (acyl is formyl or acetyl), both residue at of 8-O-methyl-N-acetylneuraminic acid being attached to theN-acylgalactosamine residue at positions 3 and 6. The minor components are disialogangliosides with linear carbohydrate chains in which the terminal sialic acid residue is attached to the penultimateN-acetylneuraminic acid residue at positions 4, 8, or 9. The lipid part of the gangliosides consists of sphingenine and unsubstituted fatty acids (mainly, palmitic and stearic acids). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–161, January, 2000.     

Gangliosides from the starfishEvasterias echinosoma: identification of a disialoganglioside containing 8-O-methyl-N-acetylneuraminic acid andN-formylgalactosamine

Gangliosides were isolated from the starfishEvasterias echinosoma and their structures were elucidated by chemical and physicochemical methods. Two major gangliosides were found to be disialogangliosides, whose carbohydrate chain is based on the trisaccharide β-N-acylgalactosaminyl-(l→3)-β-galactosyl-(l→4)-β-glucose (acyl is formyl or acetyl), both residue at of 8-O-methyl-N-acetylneuraminic acid being attached to theN-acylgalactosamine residue at positions 3 and 6. The minor components are disialogangliosides with linear carbohydrate chains in which the terminal sialic acid residue is attached to the penultimateN-acetylneuraminic acid residue at positions 4, 8, or 9. The lipid part of the gangliosides consists of sphingenine and unsubstituted fatty acids (mainly, palmitic and stearic acids). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 156–161, January, 2000.     

Dual inhibition of mycobacterial fatty acid biosynthesis and degradation by 2-alkynoic acids

2-Hexadecynoic acid and 2-octadecynoic acid have cidal activity against Mycobacterium smegmatis and Mycobacterium bovis BCG. At subinhibitory concentrations, M. smegmatis rapidly transformed [1-(14)C]-2-hexadecynoic acid into endogenous fatty acids and elongated them into mycolic acids. Toxic concentrations of 2-hexadecynoic acid resulted in accumulation of 3-ketohexadecanoic acid, which blocked fatty acid biosynthesis, and 3-hexadecynoic acid, an inhibitor of fatty acid degradation. The combination of these two metabolites is necessary to achieve the inhibition of M. smegmatis. We conclude that 2- and 3-hexa/octadecynoic acids inhibit mycolic acid biosynthesis, fatty acid biosynthesis, and fatty acid degradation, pathways of significant importance for mycobacteria.     

Synthesis of Lacto‐ and Neolacto‐series Ganglioside Analogs Containing N‐Glycolylneuraminic Acid: Probes for Investigation of Specific Receptor Structures Recognized by Influenza A Viruses

Sialic acids are essential components of host‐cell surface receptors for infection of influenza virus. To investigate the specific receptor structures recognized by various influenza A viruses, a series of lacto‐ and neolacto‐series ganglioside analogs containing N‐glycolylneuraminic acid (Neu5Gc) have been synthesized. The pentasaccharide structures of Neu5Gc‐α‐(2→3)/(2→6)‐lactotetraose (IV³⁽⁶⁾Neu5GcLcOse) and Neu5Gc‐α‐(2→3)/(2→6)‐neolactotetraose (IV³⁽⁶⁾Neu5GcnLcOse) were constructed by glycosylation of the suitably protected trisaccharide acceptors (2A and 2B) with the Neu5Gc‐α‐(2→3)/(2→6)‐Gal trichloroacetimidate donors (1 and 21), respectively. Transformation of the 2‐(trimethylsilyl)ethyl group at the reducing end in 4, 11, 23, and 30 into the trichloroacetimidate group gave a series of Neu5Gc‐α‐(2→3)/(2→6)‐lacto‐ and neolactotetraose donors (7, 13, 26, and 33), which were coupled with 2‐(tetradecyl)hexadecanol (8), to give the corresponding glycolipids (9, 14, 27, and 34). Finally, the complete removal of the O‐acyl groups and saponification of the methyl ester group gave the desired ganglioside analogs (10, 15, 28, and 35).     

Hydrophobic match between cholesterol and saturated fatty acid is required for the formation of lamellar liquid ordered phases

Palmitic acid and cholesterol have been shown to form, under certain conditions, bilayers in the liquid ordered (lo) phase. In the present work, the contribution of the hydrophobic match between cholesterol (chol), and the acyl chain of saturated fatty acids (FA) has been examined. The behavior of FA/chol mixtures where the FA acyl chain length was varied between 12 and 24 carbon atoms was investigated by infrared and 2H NMR spectroscopy, as well as by differential scanning calorimetry. It was found that only fatty acids with acyl chains of 14-18 carbon atoms lead to the formation of lo phase bilayers. The length of these chains corresponds, in fact, to the length of the long axis of the cholesterol molecule. Therefore, the hydrophobic match between the apolar parts of the molecular constituents appears to be a requisite for the formation of lamellar lo phases.     

Synthesis and Biological Evaluation of the Forssman Antigen Pentasaccharide and Derivatives by a One‐Pot Glycosylation Procedure

The synthesis and biological evaluation of the Forssman antigen pentasaccharide and derivatives thereof by using a one‐pot glycosylation and polymer‐assisted deprotection is described. The Forssman antigen pentasaccharide, composed of GalNAcα(1,3)GalNAcβ(1,3)Galα(1,4)Galβ(1,4)Glc, was recently identified as a ligand of the lectin SLL‐2 isolated from an octocoral Sinularia lochmodes. The chemo‐ and α‐selective glycosylation of a thiogalactoside with a hemiacetal donor by using a mixture of Tf₂O, TTBP and Ph₂SO, followed by activation of the remaining thioglycoside, provided the trisaccharide at the reducing end in a one‐pot procedure. The pentasaccharide was prepared by the α‐selective glycosylation of the N‐Troc‐protected (Troc=2,2,2‐trichloroethoxycarbonyl) thioglycoside with a 2‐azide‐1‐hydroxyl glycosyl donor, followed by glycosidation of the resulting disaccharide at the C3 hydroxyl group of the trisaccharide acceptor in a one‐pot process. We next applied the one‐pot glycosylation method to the synthesis of pentasaccharides in which the galactosamine units were partially and fully replaced by galactose units. Among the three possible pentasaccharides, Galα(1,3)GalNAc and Galα(1,3)Gal derivatives were successfully prepared by the established method. An assay of the binding of the synthetic oligosaccharides to a fluorescent‐labeled SLL‐2 revealed that the NHAc substituents and the length of the oligosaccharide chain were both important for the binding of the oligosaccharide to SLL‐2. The inhibition effect of the oligosaccharide relative to the morphological changes of Symbiodinium by SLL‐2, was comparable to their binding affinity to SLL‐2. In addition, we fortuitously found that the synthetic Forssman antigen pentasaccharide directly promotes a morphological change in Symbiodinium. These results strongly indicate that the Forssman antigen also functions as a chemical mediator of Symbiodinium.     

Synthesis of three regioisomers of the pentasaccharide part of the Skp1 glycoprotein of Dictyostelium discoideum

Three regioisomers of the linear pentasaccharide part of the Skp1 glycoprotein, found in Dictyostelium discoideum, were prepared in the form of (2-trimethylsilyl)ethyl glycosides by means of 2+3 block syntheses using the disaccharide donor at the non-reducing end, and three different trisaccharide acceptors at the reducing end. Fucosylation of (2-trimethylsilyl)ethyl 3,4,6-tri-O-benzyl-β-d-galactopyranosyl-(1→3)-4,6-O-benzylidene-2-deoxy-2-NPhth-β-d-glucopyranoside with different fucosyl donors carrying an O-(2-naphthyl)methyl ether as a temporary-protecting group at positions C2, C3 or C4 gave rise to the protected core trisaccharides. After selective removal of the (2-naphthyl)methyl group, the resulting acceptors were glycosylated with the α(1→6) linked digalactosyl donor to yield the respective three regioisomeric pentasaccharides. Transformation of the phthalimido moiety into an N-acetyl group, followed by catalytic hydrogenation of the reducible-protecting groups furnished the free target pentasaccharides, which should be able to assist during the elucidation of the exact structure of the natural pentasaccharide.     

Total synthesis of the aminopropyl functionalized ganglioside GM1

GM1 is a common ganglioside pentasaccharide present on mammalian cell surface.It has been shown to play important roles in cellular communications and initiation of β-amyloid aggregation.In order to synthesize GM1,an efficient synthetic route was developed via a [3+2] strategy.The GM3 trisaccharide acceptor bearing an azido propyl group at the reducing end was prepared using the traditional acetamide protected sialyl thioglycosyl donor,which gave better stereoselectivity than sialyl donors protected with trichloroacetamide or oxazolidinone.The glycosylation of the axial 4-hydroxyl group of GM3 by the disaccharide donor was found to be highly dependent on donor protective groups.Donor bearing the more rigid benzylidene group gave low glycosylation yield.Replacing the benzylidene with acetates led to productive coupling and formation of the fully protected GM1 pentasaccharide.Deprotection of the pentasaccharide produced GM1 functionalized with the aminopropyl side chain,which will be a valuable probe for biological studies.     

Analysis by fast-atom bombardment tandem mass spectrometry of phosphatidylcholine isolated from heart mitochondrial fractions: Evidence of incorporation of monohydroxylated fatty acyl moieties

Phosphatidylcholine (PC) is one of the main phospholipids present in mitochondrial membranes. According to current knowledge, the predominant fatty acyl moieties in this phospholipid are 16, 18, 20, or 22 carbon atoms long with chains that contain only carbon and hydrogen atoms. We have conducted a detailed analysis of the fatty acid substituents of the phospholipids present in mitochondrial fractions by using fast-atom bombardment tandem PC extracted from mitochondrial fractions of rat heart. The structure of one of these monohydroxylated fatty acids has been elucidated and corresponded to 12-hydroxy 9-octadecenoic acid. Indications that concern the structure of the five other monohydroxylated fatty acids are presented. These monohydroxylated fatty acyl groups are preferentially associated in the PC molecule with C-18 and C-20 fatty acyl moieties. We present arguments to suggest that the formation of these compounds is probably not due to a free-radical initiated mechanism. The potential implication of these monohydroxylated fatty acids in several physiological functions is suggested by the fact that free hydroxylated fatty acids that are identical or closely related to those found in the mitochondrial fractions possess various biological activities.     

Biomimetic monoacylation of diols in water. Lanthanide-promoted reactions of methyl benzoyl phosphate

The direct monoacylation of diols by acyl phosphate monoesters in water is a biomimetic analogy to the enzymic aminoacylation of tRNA by aminoacyl adenylates. Without catalysis, acyl phosphate monoesters react rapidly with amines but very slowly with water and alcohols. Lanthanide ions dramatically and selectively facilitate the base-catalyzed monoacylation of diols in water by methyl benzoyl phosphate (MBP), a typical acyl phosphate monoester, in neutral solutions where reactive amines are protonated and unreactive. The reaction patterns and reactivity of various diols with MBP in the presence of lanthanides are consistent with a mechanism that involves internal addition from the conjugate base of the bis-bidentate complex of the lanthanide with the diol and MBP. The method is also applicable to reactions of nucleosides as evidenced by the selective monoacylation of the 2'- or 3'-hydroxyl group of adenosine, without reaction of the 5'-hydroxyl group or the 6-amino group. Analogues of adenosine without the diol are unreactive. This suggests that the method will selectively monoacylate the hydroxyl groups at the unique diol in tRNA that forms the 3'-terminus.     

Lipidomics of the Edible Brown Alga Wakame (Undaria pinnatifida) by Liquid Chromatography Coupled to Electrospray Ionization and Tandem Mass Spectrometry

The lipidome of a brown seaweed commonly known as wakame (Undaria pinnatifida), which is grown and consumed around the world, including Western countries, as a healthy nutraceutical food or supplement, was here extensively examined. The study was focused on the characterization of phospholipids (PL) and glycolipids (GL) by liquid chromatography (LC), either hydrophilic interaction LC (HILIC) or reversed-phase LC (RPLC), coupled to electrospray ionization (ESI) and mass spectrometry (MS), operated both in high and in low-resolution mode. Through the acquisition of single (MS) and tandem (MS/MS) mass spectra more than 200 PL and GL of U. pinnatifida extracts were characterized in terms of lipid class, fatty acyl (FA) chain composition (length and number of unsaturations), and regiochemistry, namely 16 SQDG, 6 SQMG, 12 DGDG, 5 DGMG, 29 PG, 8 LPG, 19 PI, 14 PA, 19 PE, 8 PE, 38 PC, and 27 LPC. The FA (C16:0) was the most abundant saturated acyl chain, whereas the monounsaturated C18:1 and the polyunsaturated C18:2 and C20:4 chains were the prevailing ones. Odd-numbered acyl chains, iJ., C15:0, C17:0, C19:0, and C19:1, were also recognized. While SQDG exhibited the longest and most unsaturated acyl chains, C18:1, C18:2, and C18:3, in the sn-1 position of glycerol, they were preferentially located in the sn-2 position in the case of PL. The developed analytical approach might pave the way to extend lipidomic investigations also for other edible marine algae, thus emphasizing their potential role as a source of bioactive lipids.