Complex glycans

Some of the multibranched complex glycans of hen ovomucoid have been analyzed by f.a.b.-m.s. together with e.i.-m.s. These glycans exhibit exceptional structural features, because their mannotriose core can be highly substituted, as shown in 25. All samples gave abundant [M+Na]" ions when analyzed as their permethylated alditols, and this permitted the... 

Fig. 15.1. The A/-glycan biosynthetic pathway, illustrating how the three classes of A/-glycans (high mannose, hybrid and complex glycans) are derived from a common biosynthetic precursor. The trimannosyl-chitobiose core, which is common to all A/-glycans, is outlined on the precursor A/-glycan. Glc, o Man, GIcNAc.

The following method for carbohydrate conjugation to dendrimers may be used to couple a variety of reducing sugars to amine-dendrimers, including saccharides, longer-chain carbohydrates, and even complex glycans after release from a protein (see Chapter 1, Section 4.6). 

Gal/GalNAc or Man/GlcNAc, there are also receptors (e.g., the macrophage sialic acid receptor) for the recognition of sialylated complex glycans.10... 

However, the azide-based protocol often has problems with the formation of byproducts under both azide formation and subsequent reduction. 388 Therefore, mainly aminolysis is used. Glycosylamines are prepared from GlcNAc, GlcNAc2, Glc, maltotriose, mal-toheptaose, and di- and triantenneary complex glycans, isolated from asialofetuin by preparative hydrazinolysis. A modification of the method by Likhosherstov is also employed. 379 ... 

For the study of polyprenyl glycosyl phosphates as intermediates in the synthesis of complex glycans, several techniques have been developed, and these have been described elsewhere in detail.18 20 Two important features should be emphasized. First, the very small amounts of polyprenyl phosphates that are present in most tissues for this reason, the use of radioactive techniques for the detection of products is obligatory. Second, on account of the hydrophobic nature of these compounds, and as the enzymes involved in the reactions are membrane-bound, the use of detergents and organic solvents becomes necessary. 

D. J. Harvey, R. H. Bateman, R. S. Bordoli, and R. Tyldesley, Ionisation and fragmentation of complex glycans with a quadrupole time-of-flight mass spectrometer fitted with a matrix-assisted laser desorption/ionisation ion source, Rapid Commun. Mass Spectrom., 14 (2000) 2135-2142. 

A diverse range of glycan forms may be produced in some recombinant proteins. For example, the HIV envelope glycoprotein (gpl20) produced from CHO cells contains 24 occupied sequons, of which 13 are complex glycans and 11 are high mannose or hybrid structural forms (Leonard etal., 1990). 

The assembly of complex glycans via either a linear or a block approach is often subject to tedious purification (chromatography) steps that lower the overall chemical yield. It would be desirable to use an approach that strives to lower the number of purifications, particularly as the synthesis advances. Toward this end, many groups have developed and refined one-pot... 

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