Glycopeptides formation

Saha, U. and Schmidt, R. (1997) Efficient synthesis of 0-(2-acetamido-2-deoxy-(3-D-glucopyranosyl)-serine and -threonine building blocks for glycopeptide formation./. Am. Chem. Soc. Perkin TransI., 1855-1860. 

Spiro RG Protein glycosylation nature, distribution, en2ymatic formation, and disease implications of glycopeptide bonds. Glycobiology 2002 12 43R-... 

A typical procedure calls for reaction of the hemiacetal donor with dicydohexyl carbodiimide and copper(I) chloride (0.1 equiv) at 80 °C, followed by an addition of the acceptor and continued heating. As an early demonstration of this protocol, oc-riboside 86 was prepared in moderate yield but with exclusive stereoselectivity [141]. Further measures were required for the glycosylation of monosaccharide acceptors, such as addition of p-toluenesulfonic add (0.1 equiv) to promote the formation of disaccharide 87 [144]. The method was more suitably applied to the synthesis of O-acyl glycopeptides, as evidenced by the formation of 88 in 60% yield [143,144]. Various peptides with non-nudeophilic side chains were found to be amenable to this stereoselective reaction. The [3-selectivity was suggested to arise from a preponderance of the a-isourea intermediate 85 in the activation step. 

III. 3-6>-Glycopeptides of l-Serine or l-Threonine 1. Formation of the 3-O-Glycosidic Linkage... 

Carboxylic acid-terminated organosilanes were used in the early studies on chemically bonded glycopeptides to immobilize vancomycin and thiostrepton via then-amino groups, leading to the formation of stable amide bonds between antibiotics and modified silica [7]. In a typical reaction, 4 g of dry silica gel is slurried on 50 mL of dry toluene. Two grams of [l-(carbomethoxy)ethyl]methyldichlorosilane or [2-(carbomethoxy)ethyl]trichlorosilane is dissolved in 15 mL of dry toluene contained in a dropping flask. The organosilane solution is added dropwise over 30 min... 

For glycopeptide synthesis, much attention has to be paid to the stereoselective formation of the natural-type glycosidic bond which must remain unchanged in the course of the synthesis. Therefore, in comparison to peptide synthesis, the compatibility and chemoselectivity of the applied reaction is fundamental in glycopeptide synthesis. 

Scheme 1 Potential Side Reactions of Glycopeptides (A) with Acid, (B) with Base, and (C) by Aspartimide Formation 47-49 ...

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