Glycal epoxide method

The glycal epoxide method turned out to be useful for the construction of complex 2-branched [3-aryl glycosides, which are salient features of the potent antibiotic vancomycin [75a]. Glycal epoxide glycosylation with sodium salts of indoles pro-... 

The glycal epoxide method was also applied to the synthesis of a-O-glycosides [133] and of 2-deoxy-(5-0-glycosides [134]. Although interesting results were reported in both cases, other strategies seem to be preferable for these purposes (see sections 3.3 and 3.5). 

The glycosidic bonds present in KS-502 and rebeccamycin provided especially attractive contexts for evaluation of the glycal epoxide method (Scheme 13). Treatment of the furanose glycal with DMDO gave the furanose epoxide 69 ster-eoselectively [38]. Reaction of this epoxide with the phenol 70 afforded an 81% yield of the desired aryl-glycoside 71. Subsequent steps completed the synthesis of KS-501 (42) and KS-502 (43). These furanoid epoxides were also used in the synthesis of nucleosides [39]. 

Evans developed a new method for the synthesis of [(-C-allylglycosides, based on BusSnOTf-mediated ring-opening of glycal epoxides with allylstannanes as nucleophiles [81a], This methodology has been efficiently used in the (3-stereoselective introduction of the side chain (C44-C51) of spongistatin 2 (Scheme 8.43) [81b,c]. 

R. J. Patch, H. Chen, and C. R. Pandit, Multivalent templated saccharides Convenient syntheses of spacer-linked 1, l -bis -and 1, 1, 1 "-tris-/i-glycosides by the glycal epoxide glycosidation method, /. Org. Chem., 62 (1997) 1543-1546. 

An early example of the 1,2-participation-migration strategy termed the glycal assembly method was developed by Samuel Danishefsky and coworkers (Scheme 4.5a) [22], In this approach, the double bond of a glycal is converted into an epoxide or... 

Glycal assembly method (Section 25.9) a method of polysaccharide synthesis in which a glycal is converted into its epoxide, which is then opened by reaction with an alcohol. 

Several efficient methods for the preparation of amino sugars have been developed57 and the following general methods can be identified nucleophilic displacement reactions, epoxide opening, additions to glycals, reduction of oximes and intramolecular substitutions. 

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