Intramolecular glycosylation reaction

Monocyclic Ar-thiocarbonyl iminosugars are highly prone to undergo intramolecular glycosylation reactions when the resulting bicyclic structures... 

Another cyclomaltohexaose isomer was synthesized in which the D-glucose residues were replaced by D-mannose residues [63,64]. The key intermediate was the formation of a mannohexaosyl methylthioglycoside that was cyclized by an intramolecular glycosylation reaction using phenylselenyl triflate as a catalyst. 

The activation of NPGs during a glycosylation reaction (Scheme 5.7a) depends on electrophilic addition to the olefin (—>111), followed by intramolecular displacement by the anomeric oxygen to form the oxonium species IV. Trapping with a glycosyl... 

The enzyme activity is widely distributed in bacteria, yeasts, plants, and animals, and catalyzed by at least live structurally distinct enzyme groups (Takaha and Smith, 1999) as shown in Table 28.3. In addition to the inter-molecular trans-glycosylation reaction expressed in equation (4), 4aGT also catalyze the intramolecular transglycosylation reaction (cyclization reaction) of a-1,4 glucan to produce cyclic a-1,4 glucan as shown in equation 28.5 ... 

SCHEME 13. Intramolecularly H-bonded acceptors, which led to misreactivity in glycosylation reactions. 

T.-H. Tang, D. M. Whitfield, S. P. Douglas, I. G. Csizmadia, and J. J. Krepinsky, Differential reactivity of carbohydrate hydroxyls in glycosylation reactions I Intramolecular interaction of the 5 -hydroxyl group with the heteroaromatic base in a model compound of 2-deoxy-cytidine, Can. J. Chem., 70 (1992) 2434-2448. 

Tethering through dialkoxysilanes. The linking of hydroxyl groups from two molecules favor their subsequent reaction. More important, the tactic affords stereo-control in these reactions, as shown in an intramolecularized glycosylation. 

A. Chenede, E. Perrin, E. D. Rekai, and P. Sinay, Synthesis of C-disaccharides by a samarium diiodide induced intramolecular coupling reaction of tethered sugars, Synlett p, 420 (1994). P. de Poully, A. Chenede, J.-M. Mallet, and P. Sinay, Smlj-promoted chemistry at the anomeric center of carbohydrates. Reductive formation and reaction of glycosyl samarium (III) reagents Bull. Soc. Chim. Fr. 730 256 (1993). 

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