Model, glycosylation

Model glycosylations aimed at the synthesis of pradimicin-benanomicin antibiotics have used fluoride 105 as a donor in a range of acceptors including anthracene derivative 106. ... 

For the synthesis of HA oligosaccharides, model glycosylations were carried out in solution and on PEG support. A glucosamine acceptor coupled with hydrojyl-terminated PEG monomethyl ether 11 was efficiently glycosylated with trichloroacetimidate donor 10 afford an orthogonally protected disaccharide 12 which can be used for the synthesis of HA sequences, see Scheme 3. 

Scheme 10 Model glycosylation reaction with donor 53.

Scheme 19 Synthesis of Kdo thioglycosides and model glycosylation reactions.

Fig. 12. Model for the P-adenergic receptor. It is proposed that the receptor possesses seven hydrophobic heUces that span the plasma membrane and are connected by alternating extracellular and intracellular loops (79). The site of glycosylation is represented as CHO. Reprinted with permission from Elsevier...

The effects of pH under model conditions (0.6 to 5.5 for 24 hr) were covered by Nielsen et al. for four anthocyanins (3-O-glucoside, glycosylated cyanidin, rutinoside, and delphinidin rutinoside). After 24 hr, over 90% of the anthocyanins were intact up to pH 3.3, while instabihty greatly increased at pH greater than 4.5. 

The glycosyl-linkage compositions of our three RG-II preparations were similar (Table 2) and corresponded to the relative sugar molar ratios obtained from compositional (TMS derivatives) analyses indicating that methylation was complete. Almost all the methyl ethers obtained could be attributed to known residues of the RG-II molecule (Figure 1) and our data were in accordance to that previously reported for RG-II from different plant origins [3,8,12,20,26]. The relative molar ratios of these "characteristic" methyl ethers (calculated on the basis of 1 residue of 3,4-linked fucose) were almost all in stoichiometric amounts (Table 3), confirming thus that our three preparations corresponded to the accepted model for RG-II. 

Fig. 3. (A) Disposition of afi unit in the membrane, based on sequence information [14,15], selective proteolytic digestion of the a subunit [5,6] and hydrophobic labelling (Table 1). The model for the (S subunit is based on sequencing of surface peptides and identification of S-S bridges [64,65]. T, T2 and C3 show location of proteolytic splits. CHO are glycosylated asparagines in the P subunit. (B) Peptide fragments remaining in the membrane after extensive tryptic digestion of membrane-bound Na,K-ATPase from outer medulla of pig kidney as described by Karlish et al. [7,58].

Hunt, J.V., Dean, R.T. and Wolff, S. (1988). Hydroxyl radical production and autoxidative glycosylation. Glucose oxidation as the cause of protein damage in the experimental glycation model of diabetes mellitus and ageing. Biochem. J. 256, 205-212. 

D-Gal — hydroxy-L-histidine,4950 d-G1cA — hydroxy-L-tryptophan,51 d-GlcA — hydroxy-L-phenylalanine,51 d-G1cA — L-Ser,51 and carbohydrates N-glycosylated to the a-amino group of the N-terminal portion of proteins.51-53 Most of these compounds will be discussed in more depth later in this article, in terms of model compounds for oligosaccharide linkages to proteins. 

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... 

C-N.m.r. Chemical-shift Data for Glycopeptides Carrying a Glycosyl Group1 at the C-Terminal Part of the Peptide, and also for Some Related Model Compounds... 

Fig. 8.1 Hypothetical two-dimensional model of human P-glycoprotein. Small circles amino acid residues large circles ATP sites squiggly lines N-linked glycosylation sites (modified from [15]).

T. A. Gerken, Kinetic modeling confirms the biosynthesis of mucin core 1 (/i-Gal (1 -3)x-Gal YAc-O-Ser/Thr) O-glycan structures are modulated by neighboring glycosylation effects, Biochemistry, 43 (2004) 4137—4142. 

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