Synthetic Strategies for Carbon-Linked Disaccharides and Pseudosaccharides

223 SYNTHETIC STRATEGIES FOR CARBON-LINKED DISACCHARIDES AND PSEUDOSACCHARIDES 

Furan was identified as a masked sugar synthon for the stereoselective synthesis of d-and L-C4-C5 linked disaccharides. The d- and L-furanyl saccharides (45a and 45b) (1.8 1) obtained from the aldehyde (44) on oxidative umnasking gave the enone system (46a and 46b). Stereoselective reduction of the enone followed by cw-hydroxylation offered the C—C linked d-(47) and L-(48a and 48b) disaccharides. Thus, the de novo construction of a sugar moiety employing furan as a masked sugar synthon led to the distereospecific 

In a further study on the carbon-linked disaccharides, the Wittig ylide (69), a C4 synthon, derived from ethyl acetoacetate, was envisaged as a homolagative precursor for the 

CH2CL2, RT (d) CeCLa.THjO, NaBH4, MeOH, 0°C (e) EtjN, CHjClj (f) 0s04, NMO, ac-etone/water (4 1). 

Spiroacetal function is a characteristic substructure of several biologically important natural products that are produced from many sources,among which papulachan-drins A to represent a pyranoside-based spiroacetal class of natural products with 

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