Glycosylation intramolecular

Scheme 5.101 Concepts for intramolecular glycosylation. X= leaving group, Nu glycosy acceptor.

Table 5.6A Intramolecular glycosylations via prearranged glycosides - glucose donors.

One aspect, besides the size of the ring that forms upon intramolecular glycosylation, governing the stereoselective outcome using this concept has been shown to be... 

Yet another approach uses peptides as tethers for intramolecular glycosylations via prearranged glycosides (Scheme 5.113) [326,327]. The regio- and anomeric selectivity of the intramolecular glycosylation depends on the amino acid sequence of the peptide, which links glycosyl donor and acceptor. 

An approach to the total synthesis of cyclodextrins is outlined. Intramolecular glycosylative cyclizations are investigated as the key step, using appropriately protected malto-ollgosyl fluorides, for successful synthesis of completely protected cyclomalto-hexa-, hepta-, and -octaoses. Deprotection of these Intermediates afforded the desired, unsubsituted cyclodextrins. 

Retrosynthetic analysis of cydodextrins led us to design a linear, key intermediate U which could be suitable for a possible intramolecular glycosylation for the synthesis of alpha, gamma, and some isomeric cydodextrins, according to the kind of protective group at C-6 of the nonreducing glucopyranosyl residue,... 

The crucial intramolecular glycosylation of 6 with SnCl2— Ag0S02CF2 afforded a 20% yield of compound 5 the latter was debenzylated with Pd-C—HCO2H—Me0H(1 0) to give cyclomaltohexaose (alpha oyclodextrin) quantitatively. 

In conclusion, by employing three key intermediates 6, 29, and 30, intramolecular glycosylative ring closures were executed to afford alpha, gamma, and "iso-alpha" oyclodextrins, respectively.(11)... 

Laursen, J B, Petersen, L, Jensen, K J, Intramolecular glycosylation under neutral conditions for synthesis of 1,4-linked disaccharides, Org. Lett., 3, 687-690, 2001. 

Other methods of preparation of these valuable compounds are shown in O Scheme 3. All of them are based on the intramolecular glycosylation of glycals by a terminal hydroxyl group. Treatment of the 3,4-di-O-benzoyl-D-glucal (4 R = Bz) with iodonium dicollidine perchlorate (IDCP) results in formation of the anhydro derivative 5a (R = Bz), while activation of the hydroxyl group in a free glycal (4 R = H) with (Bu3Sn)20 followed by iodocyclization pro-... 

Intramolecular Glycosylation Approach to the Synthesis of 1,4-Linked Disaccharides... 

DISAL-Based intramolecular glycosylation approach to 1,4-linked disaccharides... 

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