C-Oligosaccharides

C-branched sugars or C-oligosaccharides are obtainable through indium-promoted Barbier-type allylations in aqueous media.151 Indium-mediated allylation of a-chlorocarbonyl compounds with various allyl bromides in aqueous media gave the corresponding homoallylic chlorohydrins, which could be transformed into the corresponding epoxides in the presence of a base (Eq. 8.62).152... 

In an approach towards the synthesis of C-oligosaccharide containing a-D-Man-(l )-D-Man repeating units, C-4 allylated building block 183 was designed [69]. However, the allyla-tion of iodide 181 at C-4 with allyltributyltin and AIBN or dilauoryl peroxide (DLP) slow-... 

Fig. 2. Structures of glycans found in Dictyostelium discoideum. Structures of known carbohydrate components in Dictyostelium discoideum. The structures have been determined by physical/chemical methods or by the analysis of radiolabeled materials. (A) Lipid-linked oligosaccharide precursor of N-linked oligosaccharides [14] (B) truncated lipid-linked oligosaccharide precursor found in mutant strains HL24I and HL243[I4] (C) oligosaccharide with GlcNAc residues at the intersecting position and locations of the methylphosphate esters [16].

Fig. 19.9. Composition of starch syrups (acid hydrolysis). a Glucose, b maltose (disaccharide), c oligosaccharide (degree of polymerization DP = 3-7), d higher saccharides...

The n.m.r. spectra of the blood group tetra- and hexa-saccharide alditols (16) and (17), respectively, have been fully assigned by use of COSY and HOHAHA techniques, and the and n.m.r. spectra of mil)c oligosaccharides containing the blood group determinants Le , Le , or Le have been recorded and assigned by application of 2D shift-correlation... 

Rice, K. G. and Lee, Y. C. Oligosaccharide valency and conformation in determining binding to the asialoglycoprotein receptor hepatocytes. In Advances in Enzymology and Related Areas of Molecular Biololgy 66, (A. Meister, ed.), John Wiley Sons Inc., New Jersey, pp. 41-83, 1993. 

In general, the de novo approach applied by the Kishi group for the synthesis of C-oligosaccharides relies on acyclic stereocontrol for the construction of the contiguous chiral centers of at least one of the carbohydrate moieties. The first examples of this approach were reported by this group in 1987 and involved the synthesis of four C-disaccharides, including the C-analogs of methyl maltoside and cellobio-side, from a common synthetic intermediate [70]. 

Applying a conceptually different approach to the de novo design of C-oligosaccharides, Vogel and coworkers described the use of stereoselective transformations on the rigid oxa-norbomane bicyclic system some examples, shown in Schemes 25 and 26 in Section 20.3.1, rely on radical reactions for assembly of the two sugar units [51-53]. 

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