Fucosyl residues

From the abalone Haliotis japonica has been isolated a neutral pentagly-cosylceramide containing one glucosyl residue, one galactosyl residue, one 2-acetamido-2-deoxygalactosyl residue, and two fucosyl residues.125 The structure of this compound has been identified, from the data given by partial and total acid hydrolysis, methylation, and H-n.m.r. spectroscopy, as... 

Paulsen and co-workers [156] have also prepared the blood group B (type 2) tetrasaccharide (324) from the lactosamine derivative (318). They attached the 2 -0-l-fucosyl residue using the fucosyl bromide (322) in the presence of mercury(II) bromide and molecular sieves and obtained (319) in 80% yield. Removal of the benzoyl group and glycosidation with 2,3,4,6-tetra-O-benzyl-oc-gaIactopyranosyl bromide in the presence of mercury(II) bromide and molecular sieves at 20 °C or with silver triflate — silver carbonate at —25 °C gave the 3 -0-a-D-galactosyl derivative (323) in 80% yield. In this paper Paulsen discusses in detail the conditions (reactivity of alcohol,... 

Nashed and Anderson [155] prepared an isomer of the blood-group B (type 2) tetrasaccharide with lactosamine substituted at the 4 -position with an a-D-galactosyl residue and at the 2 -position with an a-L-fucosyl residue. For this purpose, the lactosamine derivative (331), prepared via (330), was a-glycosylated with tetrabenzyl-galactosyl bromide in the presence of silver carbonate and silver triflate and the benzoyl group removed from the product so that the 2 -position could be fucosylated with the bromide (302) in the presence of bromide ion. If the fucose residue was added first to the lactosamine derivative (332), then the product (333) [which was converted into the trisaccharide of the blood group H (type 2)] would not react with the tetrabenzyl-galactosyl bromide. 

Lacto-N-fucopentaose II also contains an a-L-fucosyl residue linked to a lacto-iV-tetraose molecule, but in this case it is linked to C4 of the 2-acet-amido-2-deoxy-D-glucose unit. The sequence and linkages were again established by hydrolysis of the permethylated saccharide alcohol.279... 

The consitution of the hexasaccharide lacto-A7-difucohexaose has not yet been fully elucidated, but it appears to have the structure of lacto-iV-fuco-pentaose I, together with an extra L-fucosyl residue, probably linked as in lacto-AT-fucopentaose II.253... 

Figure 8. Molecular models of oligosaccharides. The line indicates the position of an arbitrary plane normal to the page above which lacto-N-tetraose (LNT) is unaltered by substitution of fucosyl residues to form lacto-N-fucopentaose I (LNF I) or lacto-N-fucopentaose II (LNF II). In lacto-N-neotetraose (LNnT) nonreducing terminal galactose projects below this plane (see Table I for the structure of the oligosaccharides).

Noel, K.D., Box, J.M., Bonne, VJ 2-O-Methylation of fucosyl residues of a rhizobial lipopolysac-charideis increased in response to host exudate and is eliminated in a symbiotically defective mutant. Appl Environ Microbiol 70 (2004) 1537-1544. 

The mechanism whereby the chain-terminating step for oligosaccharide formation is regulated is not well understood. It has been proposed that certain structural features, such as the presence of sialyl or fucosyl residues, and an uncommon anomeric configuration,138,139 act as signals to halt the synthesis of the oligosaccharide chain. Additional studies are needed in order to clarify the role of these structural features in the chain-terminating process. 

Inbar and coworkers689 determined that [3H]-acetylated lectin did not bind to the surface of normal cell-lines (hamster and rat embryo, and mouse 3T3 cells) or to the transformed counterparts of these cells. Trypsinization did not alter these results. The authors concluded688 that L-fucosyl residues were not exposed on the cell surface. In view of the specificity studies of Kabat and coworkers,200,686 this interpretation may be incorrect L-fucosyl residues may be rendered sterically inaccessible by glycosylation of neighboring sugar residues. 

Fucose has been detected in many fungi. It is formed on hydrolysis of the cell walls of the yeast-like fungi Mucor adventitius, Mucor hiemalis, Mucor javanicus, Mucor plumbeus, Mucor racemosus, Mucor spinosus, and Mucor sylvaticus, and in Rhizopus oryzae, Rhizoptts tamari, Rhizopus tonkiniensis, and Zygorrhyncus vuillemmU. The acidic, exocellular polysaccharide of Mucor racemosus contains L-fucosyl residues. ... 

Lacto- -fucopentaose / (8% of the total oligosaccharides) is a derivative of lacto-Af -tetraose in which the terminal n-galactose residue is substituted at C-2 by an a-n-fucosyl residue" and it has, therefore, been alternatively named monofuco-lacto-AT-tetraose I. The systematic name is 0-a-L-fuco-... 

Lacto- N-difucohexaose (7% of the total oligosaccharides) has not yet been fully characterized, but it appears to be a di-O-fucosyl derivative of lacto-Af -tetraose in which the a-L-fucosyl residues are linked to C-2 of the terminal n-galactose residue (as in lacto-AT-fucopentaose I) and to C-4 of the 2-acetamido-2-deoxy-D-glucose residue (as in lacto-iV-fucopentaose II). ... 

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