Glycosylation sialic acid

K. Ikeda, Y. Ueno, S. Kitani, R. Nishino, and M. Sato, Ferrier glycosylation reaction catalyzed by Bi(OTf)3-Montmorillonite K-10 Efficient synthesis of 3,4-unsaturated sialic acid derivatives, Synlett (2008) 1027-1030. 

Add 106-108cells/ml in a PBS solution (lOmM sodium phosphate, 0.15M NaCl, pFI 7.4) containing ImM sodium periodate and incubate on ice for 30 minutes in the dark. This level of periodate addition will target the oxidation only to sialic acid residues (Chapter 1, Section 4.4). If additional sites of glycosylation also are to be labeled, increase the periodate concentration to 10 mM and do the reaction at room temperature in the dark. 

The following protocol describes the use of biotin-hydrazide to label glycosylated proteins at their carbohydrate residues. Control of the periodate oxidation level can result in specific labeling of sialic acid groups or general sugar residues (Chapter 1, Section 4.4). 

Incomplete (N-linked) glycosylation prompts decreased in vivo activity due to more rapid hepatic clearance of the EPO molecule. Enzymatic removal of terminal sialic acid sugar residues from oligosaccharides exposes otherwise hidden galactose residues. These residues are then free to bind specific hepatic lectins, which promote EPO removal from the plasma. The reported plasma tm value for native EPO is 4-6 h. The tm for desialated EPO is 2 min. Comparison of native human EPO with its recombinant form produced in CHO cells reveals very similar glycosylation patterns. 

Selenoglycosides of sialic acid have been successfully prepared in excellent yields from the corresponding peracetylated glycosyl chloride with phenylselenol in the presence of N,N-di-isopropylethylamine [519]. This reagent combination succeeded where others were less effective or failed (Scheme 4.98 [520]. 

Anomeric triphenylphosphonium salts have been used as well as phenylsul-fides,but in the latter case extra stabilization is necessary (see below). Anomeric nitrosugars, which have been extensively studied in C-glycosylation reactions by Vasella, will be covered in Sect. 2.2.1 and ester enolates derived from 3-deoxy-2-ketoulosonic acids (sialic acid and KDO derivatives), which bear a structural similarity to 2-deoxy pyranosides, will be covered in Sect. 4.4. Deprotonation of anomeric phenylsulfones has been discussed in Sect. 2.1.1 and additional transformations on closely related compounds are presented in Scheme 14 [20]. Alkylation of phenylsulfone 54 with epoxide 55 provides adduct 56 which eliminates benzenesulfinic acid at room temperature to give the C(l)-alkylated glycal 57 a similar elimination is also observed with adducts derived from... 

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