Regioselectivity glycosylation using glycosyl

The synthesis of the methyl heptaglucoside 1 (Scheme 9.6) is an excellent example of a regioselective glycosylation of the primary hydroxyl in 4,6-diol using succinoylated MPEG and iodonium promoted glycosylations with thioglycoside... 

FIGURE 4A Examples of (a) glycosyl acceptors and (b) glycosyl donors used in trityl ether-assisted regioselective glycosylation. Tr, trityl. 

The synthesis of branched saccharides by multiple glycosylations onto a central monosaccharide normally requires the use of orthogonal protecting groups in the acceptor. In this context, regioselective glycosylation of diols or polyols would ease the number of protection-deprotec-tion steps in these synthetic protocols. 

Schmidt glycosylation [8b] was used twice to prepare the trisaccharide donor 17 (Scheme 9). Attempts to use xylopyranosyl imidate donor 28 in the regioselective glycosylation of diol 26, which has an equatorial 3-OH and an axial 4-OH as diol 11, were not successful. The deprotection of the anomeric allyl group of trisaccharide 29 was found to be problematic. When reactions were catalyzed by palladium spe-... 

Sinay and coworkers explored different approaches to the synthesis of the N-acetyldermosine disaccharide (IV.22) that resulted in the report of an improved synthetic route [93]. The strategy investigated initially used diol IV.5 (as an alternative glycosyl acceptor to IV.16) that relied on regioselective glycosylation of the more reactive equatorial 3-OH. This would eliminate the need for a deprotection sequence... 

Notes and discussion. This reaction exemplifies the use of lactose as a glycosyl donor with the P-galactosidase from B. circulans. Lactose has previously been shown to give good regioselective glycosylation of various glycosides as acceptor... 

Scheme 25 Dual B-/Pd-catalyzed regioselective glycosylations using pyranone-derived allylic carbonates...

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