Notes

Analysis Oligosaccharide Shows Account Sugar Chains
In addition, the absence of the dominant xylosidated- and fucosylated-type sugar chains confirms that the transformed cells can be used to produce glycoproteins without the highly immunogenic glycans typically found in plants. These results demonstrate the synthesis in plants of N-linked glycans with modified and defined sugar chain structures similar to mammalian Synthesis and NMR spectroscopic analysis of acylated pentasaccharide fragments Chemistry, The University of Alberta, Gunning-Lemieux Chemistry Centre, The mycolyl-arabinogalactan (mAG) complex, a large glycolipid composed of arabinofuranose and galactofuranose monosaccharides and mycolic acid lipids, provides mycobacteria with substantial protection from their environment. It has been proposed that the presence of flexible furanose rings in the mAG facilitates the packing of the hydrophobic mycolic acids, forming a dense protective barrier of low permeability. In a previous article, we probed this flexible scaffold hypothesis through the synthesis and NMR analysis of di- and trisaccharide fragments of the mAG acylated with linear fatty acids. However, 2'-Fucose lactose saw few conformational changes due to the presence of the acyl chains. We proposed that branched pentasaccharide glycolipids 5-8 might exhibit larger changes due to the presence of more acyl chains, and studies with these compounds are described here.

The carbohydrate portion of 5-8 was synthesized in a 1 + 2 + 2 manner. First, 2'-Fucose lactose was treated with an excess of appropriately protected thioglycoside donor to give a trisaccharide, which, following selective deprotection to a diol, was converted to the pentasaccharide in a one-pot glycosylation. The resulting differentially protected pentasaccharide gave glycolipids 5-8 upon removal of the protecting groups at the primary positions, acylation, and hydrogenolysis. The conformations of 5-8 were probed using NMR spectroscopy, and chemical shift selective filtering 1D-TOCSY spectra allowed for the determination of all the ring coupling constants. It was found that the addition of four fatty acids to the parent pentasaccharide had little effect on the conformation of the compounds in Solid-phase oligosaccharide synthesis of a small library of N-glycans.Solid-phase oligosaccharide synthesis is based on a hydroxymethylbenzyl benzoate spacer linker which is connected to the Merrifield resin (1 P). Glycosylation was performed with O-glycosyl trichloroacetimidates of glucosamine, mannose, and galactose permitting chain extension (2e, 5e), branching (4b, 7b, 8b), and chain termination (3t, 6t, 9t) with the use of O-benzyl, O-benzoyl, and N-dimethylmaleoyl as permanent and O-fluorenylmethoxycarbonyl (Fmoc) and O-phenoxyacetyl (PA) as temporary protecting groups.

The steps required on solid phase are i) glycosylation under TMSOTf catalysis, ii) selective cleavage of the temporary protecting groups, Fmoc with NEt3 and PA with equivalents of NaOMe in CH2Cl2MeOH, and iii) product cleavage from the resin with 4 equivalents of NaOMe in CH2Cl2MeOH and following O-acetylation for convenient product isolation. Thus a highly successful synthesis of a small library of seventeen N-glycan structures was made possible comprising the N-glycan pentasaccharide core structure 53 and two further chain extended hexa- and heptasaccharide N-glycans with a glucosamine or a lactosamine residue, respectively, which is attached to one of the mannose residues of the core structure (56 and 59).Highly efficient chemoenzymatic synthesis of novel branched thiooligosaccharides by substrate direction with glucansucrases.Continuous-flow fast atom bombardment-mass spectrometry of permethylated oligosaccharides a comparative study of direct mixture analysis with packed capillary column liquid chromatography-fast atom bombardment-mass spectrometry.Boulenguer P(1), Leroy Y, Alonso JM, Montreuil J, Ricart G, Colbert C, Duquet D, Conventional positive fast atom bombardment (FAB) and continuous-flow FAB analysis were carried out with permethylated lacto-N-tetraose. This latter method, a new approach, has been used to analyze a mixture of permethylated oligosaccharides by liquid chromatography-mass spectrometry (LC-MS) with a packed capillary fused-silica column and the continuous-flow probe as interface. Under these conditions, we found the continuous-flow probe to be superior to the conventional probe because its low matrix level increased the signal-to-noise ratio.
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