Synthesis of a-gal epitope

Figure 11 Synthesis of a-gal tri- and pentasaccharide epitopes with the bifunctional protein gaZE-al,3-GT.

In general, it is difficult to express mammalian glycosyltransferases in E. coli, but some examples have been reported. " Wang s group used a truncated bovine al,3-galactosyltransferase for the synthesis of a series of a-Gal epitope derivatives for xenotransplantation. The enzyme was expressed successfully in E. coli after the deletion of the transmembrane domain." ... 

Dehydrativeglycosylation of 1-hydroxy donors with Ph2S0/Tf20 in conjunction with thioglycoside acceptors opens the way for sequential double glycosylation, one-pot procedures for trisaccharide synthesis, as exemplified by the efficient one-pot synthesis of the a-Gal epitope and a hyaluronan trisaccharide [566]. This study also shows the potential of selenoglycoside as acceptors in dehydrative glycosylation (Scheme 4.112). 

The commercially available enzymes have been employed in the synthesis of a large variety of natural and imnatural oligosaccharides [63-65]. The cost of nucleotide-sugar donors is also very high. UDP-Gal, used in the synthesis of the well-known a-gal (Galal-3Gal-R) epitopes is listed at 4000/g, making its stoichiometric use prohibitively expensive. 

Berger, E.G., Elling, L., Wandrey, C., and Uese, A. (2001) Chemo-enzymatic synthesis of the Galili epitope Gal(alpha)(l->3)Galbeta(l->4)GlcNAc on a homogeneously soluble PEG polymer by a multi-enzyme system. Bioorg. Med. Chem. Lett., 11, 2503-2506. 

Scheme 3. Recycling of UDP-Gal employing sucrose synthetase for the one-pot synthesis of the a-gal epitope.

Hanessian, S, Huynh, H K, Reddy, G V, Duthaler, R O, Katopodis, A, Streiff, M B, Kinzy, W, Oehrlein, R, Synthesis of Gal determinant epitopes, their glycomimetic variants, and trimeric clusters — relevance to tumor associated antigens and to discordant xenografts. Tetrahedron, 57, 3281-3290, 2001. 

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