Sialyltransferases oligosaccharides

Example 5 Hayakawa and Noyori group in their studies on new activators for phosphoroamidite coupling reactions have applied the most effective member of the group of acid/azole complexes AT-(phenyl)imidazolium tri-flate (N-PhIMT) in the efficient synthesis of biologically important compounds [20j]. A noteworthy example is synthesis of cytidine-5 -monophos-pho-AT-acetylneuraminic acid. This compound is a source of sialic acid in the sialyltransferase-catalysed biosynthesis of sialyl oligosaccharides [25]. 

Substrate-specificity studies on microsomal, frog-liver sialyltrans-ferase revealed the presence of (2—>3) and (2—>6) activities.277 This enzyme system readily sialylates oligosaccharides, but is almost inactive with asialofetuin, which is in contrast to the sialylation of oligosaccharides, as well as asialofetuin, by rat-liver sialyltransferase.278 The conclusion from this observation is that acceptor specificity of sialyl-transferases isolated from liver of evolutionary distant animals is similar for substrates of low molecular weight, but differs for compounds of high molecular weight.279... 

G. F. Herrmann, Y. Ichikawa, C. Wandtey, F. C. A. Gaeta, J. C. Paulson, and C.-H. Wong, A new multi-enzyme system for a one-pot synthesis of sialyl oligosaccharides Combined use of P-galactosidase and a(2,6)-sialyltransferase coupled with regeneration in situ of CMP-sialic acid, Tetrahedron Lett. 34 3091 (1993). 

It is conceivable that the natural receptor binding structure for Sendai virus has only one terminal NeuAc residue, but it is also possible that some of the oligosaccharide moieties received a disialosyl linkage during the incubation with the specific sialyltransferase. 

Fig. 8. Enzymatic glycosylation in the solid-phase synthesis of oligosaccharides elongation of the glycopeptide with /M, 4-galactosyltrans-ferase and a-2,3-sialyltransferase. The glycopeptide is finally released by cleavage with a-chymotrypsin.

Sialyltransferases transfer sialic acid moieties as the terminal residues in oligosaccharide side chains of animal cell coat proteins and gangliosides. In this assay, CMP-7V-acetylneuraminic acid was reacted with asialoglycoprotein to form cytidfne 5 -monophosphate (CMP) and the O-acetylneuraminic acid derivative of the protein. 

Enzymatic glycosylation on SP was first reported by Schuster et al. (157) and since then has been used to perform multiple glycosylations. Two examples are reported in Fig. 2.28. The synthesis of oligosaccharides 2.94 and 2.95 related to the sialyl Lewis X antigen was carried out via glycosylations mediated by P-l,4-galactosyltransferase and a-2,3-sialyltransferase (171) and by p-l,4-galactosyltransferase, a-2,3-sialyl-transferase, and fucosyltransferase (172), respectively. The use of unprotected saccha-... 

CMP-neuraminic acid can be used in oligosaccharide synthesis as a substrate for various a2-6-sialyltransferases isolated from rat liver [50] or bovine colostrum [51] as well as a2-3-sialyltransferases isolated from porcine liver [52] and porcine submaxillary glands [53]. Recently, the enzyme has been overexpressed in a baculovirus system [54]. 

Since the chemical synthesis of oligosaccharides requires many synthetic steps including protection and deprotection procedures, the enzymatic approach has attracted much attention for the rapid s)uithesis of oligosaccharides. In addition, the perfect regio- and stereoselectivities of enzymatic methods with glycosyltransferases are quite attractive. Several transferases such as 8(l,4)-galactosyltransferase, a(l,3)-fucosyltransferase, and a-sialyltransferase have been used for polymer-supported enzymatic synthesis [70,71,72,73,74,75]. The selection of the pol)uner support is very important for the pol)uner-supported enz)unatic synthesis of oligosaccharides. 

---