Immobilized glycosyl donors

Scheme 5.10 Application of NPGs in solid-phase synthesis (a) immobilization of the glycosyl donor (b) immobilization of the glycosyl acceptor.66...

Nicolaou [47] has applied this methodology in synthetic studies towards the antibiotic everinomicin 13,384-1. Glycosylation of immobilized fluoride donors such as 258 (Scheme 65) with sugar acceptors allowed the synthesis of disaccharides such as 259, attached to solid support through a selenium fink-... 

Immobilized 38 also proved to be an appropriate glycosyl acceptor when coupled with a full benzylated trichloroacetimidate donor (Scheme 10.8). Thus, TMSOTf mediated coupling of 38 with an excess of 48 gave resin-bound 49, which was further coupled with acceptor 38 to give trisaccharide 60 (60% overall yield based loading of the resin). 

Early on [84,85] it could be demonstrated that glycosyl fluorides were excellent donor substrates for glycosidases [86]. In an example immobilized a-glucosidase (EC 3.2.1.20) could be used for self transfer of a-glucopyranosyl fluoride to give isomaltose (6%), a-isomaltosyl fluoride (25%), and the trisaccharide panose (6%) [87] (O Scheme 14). 

Uridine diphosphate glucose (UDP-Glc) serves as a glucosyl donor in many enzymatic glycosylation processes. A multiple enzyme, one-pot, biocatalytic system was developed for the synthesis of UDP-Glc from low cost raw materials maltodextrin and uridine triphosphate. Three enzymes needed for the synthesis of UDP-Glc (maltodextrin phosphorylase, glucose-l-phosphate thymidyly-transferase, and pyrophosphatase) were expressed in Escherichia coli and then immobilized individually on amino-functionalized magnetic nanoparticles. The conditions for biocatalysis were optimized and the immobilized multiple-enzyme biocatalyst could be easily recovered and reused up to five times in repeated syntheses of UDP-Glc. After a simple purification, approximately 630 mg of crystallized UDP-Glc was obtained from 1 L of reaction mixture, with a moderate yield of around 50% (UTP conversion) at very low cost. ... 

Glycosylation. The use of DMTST continues to be an important way to activate thioglycosides for the synthesis of polysaccharides and other O-glycosides (e.g., eq 2), including the immobilizing of monosaccharide donors in solid-phase synthesis... 

Boons and coworkers have used the polystyrylboronic acid as a temporary polymeric support for oligosaccharide synthesis (Scheme 16.3). Polystyrylboronic acid 5, easily prepared from the corresponding bromide by treatment with trimethyl borate and n-BuLi in high loading capacity, was introduced on the 4,6-0 positions of the acceptor 6 by heating in pyridine. The immobilized boronate acceptor 7 was glycosylated with thioglycoside donor... 

---