Chemical glycosylation

Structural information chemical formula and stereochemistry in the case of a New Chemical Entity (NCE) or amino acid sequence and glycosylation sites in the case of a biotech product... 

Evidence for a glycosyl-enzyme intermediate of finite lifetime with inverting a-D-glycosidases, and details of its reaction, came from studies with 2,6-anhydro-l-deoxyhept-l-enitols and glycosyl fluorides. - Analysis of hydration and hydrolysis products on the one hand, and of glycosyla-tion products on the other, indicated an intermediate that could be approached by water from the yff-face only of the ring, and by other glycosyl acceptors only from the a-face (see Schemes 4 and 5 This can be considered a proof of the principle of microscopic reversibility of chemical reactions. 

The solubility of iridoids depends on their state (free, glycosylated, acetylated), but usually they are extracted with polar solvents methanol, ethanol, aqueous alcohols, and rarely acetone. Iridoid glycosides are more or less stable some of them are very sensitive to acids and alkalis. Some iridoid glycosides such as aucubin suffer color modification after chemical or enzymatic hydrolysis they give first a blue to green... 

Marcaurelle LA, Mizoue LS, Wilken J, et al. Chemical synthesis of lymphotactin a glycosylated chemokine with a C-terminal mucin-like domain. Chemistry 2001 7 1129-32. 

These observations have several implications for studies of glycoproteins (i) the resonances of anomeric carbon atoms that are involved in N-glycosylic linkages will be rather difficult to identify, because of their proximity to nonanomeric-carbon resonances and (ii) due to the proximity of the chemical shifts of C-l and C-5 (they are only 0.6 p.p.m. apart for / -d-G1cNAc — Asn), it may be difficult, but not impossible, to ascertain whether N-glycosylic linkages exist in the glycoprotein (see later). 

A distinct feature that may not be readily noticeable is that the chemical shift of the C-l atom of an a-D-mannosyl residue is highly dependent on its residue linkage to another a-D-mannosyl unit. The chemical shift for C-1 of an a-D-mannosyl linked to 0-2 or 0-3 of another a-D-mannosyl residue resonates at 103.5 p.p.m., whereas that of an a-D-mannosyl residue linked to 0-6 of another a-D-mannosyl unit will resonate at — 100.6 p.p.m. Moreover, if 0-2 of an a-D-mannosyl residue is glycosylated, the chemical shift of C-l of that residue will move —1.5 p.p.m. from its expected position. 

C-N.m.r. Chemical-shift Data for Various a- and /J-D-Glycosyl-L-serine Derivatives... 

Now that the general considerations concerning the 13C-n.m.r.-spec-tral data for O-glycosylated model compounds have been discussed, attention may be focused on some specific cases. Table IV gives the 13C-n.m.r.-spectral data for L-serine that has been glycosylated with various carbohydrates, such as a- and / -d-G1c, a- and /9-D-Gal, a- and / -d-Xyl, a-D-Man, and a-D-GalNAc. As mentioned earlier, the specific resonance-assignments to amino acid carbon atoms were based on chemical... 

C-N.m.r. Chemical-shift Data for the Anomeric-Carbon Atoms and C, and Coupling Constants ( /ch) Measured for Selected Gland /S-D-Glycosyl-L-threonine Model Compounds19- 1,82-84... 

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