Bis glycosides

Bicyclic aromatic [283,284] or triazole [285] spacers were used to arrange oligosaccharides in a parallel fashion to investigate mimicry of cellulose I and II. Interesting aryl C,5-bis-glycosides of type 89 (O Scheme 17) have been obtained during the work on antithrombotic 1,5-dithiopyranosides [286]. 

Crocetin (329) occurs in the stigma of saffron flowers Crocus sativd) together with crocin, the bis(glycoside) with gentiobiose of crocetin. It is used as a yellow color in foods, in the form of intact stigma rather than as an extracted dye. 

Fig. 1 Fluorescence scan of a mixture of digitalis glycosides. Digoxin (DG3), digoxigenin bis-digitoxoside (DGj), digoxigenin mono-digitoxoside (DGi), digoxigenin (DG).

Based on these results, a novel method for the synthesis of hexose-6-aldehydes from natural carbohydrate sources has been developed by us. Preliminary results for the regioselective oxidation of the primaty alcohol group in glycosides by the dinuclear copper(ll) complex N, A-bis[(2-pyridylmethyl)-l,3-diaminopropan-2-olato] (p-acetato) dicopper(ll) perchlorate (Cu2(bpdpo), (4) are described below. 

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. 

Bielawska and Michalska [511] have introduced S-(2-deoxyglycosyl)phosphor-othioates as glycosyl donors. Activation of these compounds for glycosidation with silver salts (AgF, AgC104 or AgOTf) resulted in the formation of 2 -deoxydisacchar-ides as anomeric mixtures. Thiem and coworkers reported [507] an efficient activation method for S-(2-deoxyglycosyl)phosphorothioate donors 102 by using N-iodo-succinimide (NIS) or iodonium bis(2,4,6-trimethylpyridine) perchlorate (IDCP) (Scheme 4.94). 

Anhydroalditols can be easily generated by Lewis acid catalysed reduction of the corresponding aldoses or glycosides with triethylsilane (Fig. 2). The reaction requires protection of the hydroxyl groups, which can be performed temporarily by preliminary treatment with bis(trimethylsilyl)-trifluoroacetamide (BSTFA).1... 

An interesting linker is based on bis(4-hydroxyphenyl)disulfide 3 (Scheme 9.9). Both MPEG and the carbohydrate are linked as ethers, and for removal from MPEG, the linker s disulfide bond is reductively split by propanedithiol. The carbohydrate is freed as a glycoside of 4-hydroxyphenylmercaptan.38... 

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