Disaccharides, furanosyl

The stereoselectivity in cyclizations of vinyl ether systems to form furanosyl disaccharides is controlled by both the side chain substituent (1,4-asymmetric induction) and the configuration of the existing pyranoside linkage (equation 49).142 Substrates with no side chain substituent show no stereoselectivity. 

Fluoride-induced condensation of the 5-deoxy-5-nitro furanoside 85 with the a-C-furanosyl formaldehyde 55 obtained by ring contraction of glucosamine and subsequent functional group manipulation lead to a diastereomeric mixture of the nitroaldols 86. An acetylation-elimination sequence followed by reduction of the alkene, denitration and hydrogenolysis provide the C-disaccharide 88. 

Virgilia oroboides gum contains a complex array of peripheral units, and controlled, partial hydrolysis with acid affords the disaccharides 5-O-a-L-arabinopyranosyl-L-arabinofuranose (29), 5-O-a-L-arabino-furanosyl-L-arabinofuranose (57), and 5-0-/3-D-xylopyranosyl-L-ara-binofuranose (35), together with traces of oligosaccharides to which the structures 3-O-a-L-arabinofuranosyl-L-arabinose (25) and O-a-L-arabinopyranosyl-(l - 5)-0-L-arabinofuranosyl-(l - 5)-L-arabino-furanose (58) have been assigned. 

An extensive report from Prinzbach s laboratory has described the synthesis of the pseudodisaccharide sannamycin (1), its 2-epimer and various other isomers, including the enantiomers of sannamycin and its 2-epimer. A detailed study was made of the glycosylations necessary to assemble these sytems. Various other novel pseudodisaccharides have also been prepared, including the a-D-arabino-furanosyl systems 2 (R=H, a-NHa, jJ-NHa), and the pyranose these workers also describe a Ferrier carbocyclization at the disaccharide level, using an acid labile 2 -deoxy-disaccharide, to give the aminocyclitol derivative 4. ... 

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