Glycosidases carbohydrates

A. Patel and A. C. Richardson, 3-Methoxy-4-(2 -nitrovinyl)-phenyl glycosides as potential chromogenic substrates for the assay of glycosidases, Carbohydr. Res., 146 (1986) 241-249. 

Korytnyk, W, Angelino, N, Dodson-Simmons, O, Hanchak, M, Madson, M, Valentekovic-Horvath, S, Synthesis and conformation of 5-thio-D-glucal, an inhibitor of glycosidases, Carbohydr. Res., 113, 166-171, 1983. 

E. Saman, M. Claeyssens, H. Kersters-Hilderson, and C. K. De Bruyne, Azido compounds as potential affinity labels for glycosidases, Carbohydr. Res., 30 (1973) 207-210. 

V. Ferro, L. Weiler, and S. G. Withers, Convergent synthesis of a fluorescence-quenched glycopeptide as a potential substrate for peptide JV-glycosidases, Carbohydr. Res., 306 (1998) 531-538. 

Kwan, EM Boraston, AB McLean, BW Kilburn, DG. A.J. WR. N-Glycosidase-carbohydrate-binding module fusion proteins as immobilized enzymes for protein deglycosylation. BEDS, 2005, 18(10), 497-501. 

Faijes, M. and Planas, A. (2007) In vitro synthesis of artificial polysaccharides by glycosidases and glyco-synthases. Carbohydrate Research, 342, 1581-1594. 

Moracci, M., Cobucci-Ponzano, B., Perugino, G. et al. (2005) Recent developments in the synthesis of oligosaccharides by hyperthermophilic glycosidases, in Handbook of Carbohydrate Engineering (ed. K.J. Yarema), CRC Press LLC, Boca Raton, FL, pp. 587-612. 

Trihydroxyazepanes (trideoxy-l,6-iminohexitols) have also been prepared from carbohydrate precursors and activities as inhibitors of selected glycosidase enzymes assessed... 

The synthesis of complex carbohydrate structures can preferably be accomplished using several enzymes in one-pot or sequential mode. Crude intermediate products may be either directly processed by the follow-up enzyme, or a fast and simple purification step may be included like desalting, concentrating, etc. This approach saves both time and costs, however, it requires a relatively high specificity, regioselectivity and yields in all the steps, which somehow limits the choice of glycosidases available. 

A very important group of secondary hydroxyl modifications represent fluoroglycosides.104 When they interact with a retaining glycosidase, the highly electronegative fluorine on the carbohydrate ring causes the destabilization of both transition states and the reaction proceeds at a... 

The natural substrates for many enzymes do not show any significant spectral properties and alternative artificial substrates (analogues) may be used. Many hydrolytic enzymes can most easily be detected by using substrate analogues the glycosidases, for instance, may be measured using p-nitro-phenyl derivatives of the appropriate carbohydrates. Hydrolysis results in the production of p-nitrophenol, which can be measured at 404 nm. 

Monomeric carbohydrates in their cyclic form (furanoses and pyranoses) are hemiacetals, which, to become acetals, form 0-glycosyl conjugates. The C-atom C(l) that bears two O-atoms is the reactive, electrophilic center targeted by glycosidases. Nonenzymatic hydrolysis is also possible, although, as a rule, under physiological conditions of pH and temperature, the reaction is of limited significance. 

Beau has applied the DCC concept to a number of carbohydrate systems [13-16]. Carbohydrate-binding proteins often exhibit weak ligand interactions with millimolar dissociation constants, a quite different scenario to the enzyme-small molecule DCLs discussed thus far. The protein target initially chosen for study was hen egg-white lysozyme (HEWL), a glycosidase known to bind A-acetyl-o-glucosamine (d-G1cNAc) with... 

Carbohydrates mainly occur in food in the form of polymers (starches and glycogen). They are cleaved by pancreatic amylase into oligosaccharides and are then hydrolyzed by glycosidases, which are located on the surface of the intestinal epithelium, to yield monosaccharides. Glucose and galactose are taken up into the enterocytes by secondary active cotransport with Na"" ions (see p. 220). In addition, monosaccharides also have passive transport systems in the intestine. 

Recent developments in the enzymatic synthesis of carbohydrates can be classified into four approaches 1) asymmetric C-C bond formation catalyzed by aldolases (1-10 2) enzymatic synthesis of carbohydrate synthons (loll) 3) asymmetric glycosidic formation catalyzed by glycosidases (12.-17) and glycosyl transferases (18-23.) and 4) regioselective transformations of sugars and derivatives (24-25). These enzymatic transformations are stereoselective and carried out under mild conditions with minimum protection of functional groups. They hold promise in preparative carbohydrate synthesis. In connection with this book, we focus on the first two approaches. 

---