Branched sugars

Recent progress of basic and application studies in chitin chemistry was reviewed by Kurita (2001) with emphasis on the controlled modification reactions for the preparation of chitin derivatives. The reactions discussed include hydrolysis of main chain, deacetylation, acylation, M-phthaloylation, tosylation, alkylation, Schiff base formation, reductive alkylation, 0-carboxymethylation, N-carboxyalkylation, silylation, and graft copolymerization. For conducting modification reactions in a facile and controlled manner, some soluble chitin derivatives are convenient. Among soluble precursors, N-phthaloyl chitosan is particularly useful and made possible a series of regioselective and quantitative substitutions that was otherwise difficult. One of the important achievements based on this organosoluble precursor is the synthesis of nonnatural branched polysaccharides that have sugar branches at a specific site of the linear chitin or chitosan backbone [89]. 

Pectins is a general term for a group of natural polymers based on polymerized galacturonic acid partly esterified with methanol. In addition these polymers must be considered as copolymers due to existence of neutral sugar branched zones. [1]. Some uronic acid units may also be esterified on 0-2 or 0-3 position with acetic acid. The pectins occur in the cell wall of higher plants and control at least partly the mechanical properties, the ion exchange properties and the swelling of the cell walls. 

Tables V-LVII detail H and F shift and coupling information, and Tables LVIII to LXXI incorporate the C-n.m.r. data. The data within this compilation are arranged according to the following outline hexoses prior to pentoses, followed by anhydro sugars, sugar acids and lactones, amino sugars (and their synthetic, A -containing precursors), mono-, di-, and tri-deoxy sugars, branched derivatives, ketoses, polyfluorinated monosaccharides, and, finally, difluorinated amino sugars. Within this compilation, and even within each table, pyranoid derivatives are listed prior to their furanoid counterparts, hexoses prior to pentoses, functionalized prior to deoxy compounds the arrangement within each sub-table is made alphabetically.

C-6,209,214 anhydro sugars,branched monosaccharides, fluori-nated amino sugars,difluorinated monosaccharides, and fluorinated monosaccharide phosphates,and phosphonates have been described. Further progress has been achieved in the synthesis and n.m.r.-spectral analysis of fluorinated avermectin Bu, tylono-lide, and neuraminic acid derivatives. " ... 

Deoxy sugars." Branched 2-deoxy sugars can be prepared by solvomercuration of a glycal followed by the Giese reaction with an electrophilic alkene, with marked preference for formation of an equatorial substituent. 

Interestingly, these crystal structures also make it possible to understand more subtle differences among the inhibitory effects of different macrolides. As a peptide elongates, the portion of the macrolide it first encounters will be the sugar branch that extends from C5 of the lactone ring (Fig. 4.6) towards the peptidyl... 

Branched-chain sugars. See Sugars, branched-chain. 

We will illustrate this strategy with an example found in the total synthesis of lysocellin by Yonemitsu [221,222]. As shown in Scheme 11.66, the Cl to C9 fragment was prepared by condensation of lactone 313 with the lithium salt of benzyl acetate. This part of the synthesis also serves as an illustration of sugar branching to reach a Prelog-Djerassi lactone type intermediate already mentioned in Section 11.3. A detailed discussion of this scheme follows. 

Aldol reaction Aza-sugars Branched-chain sugars Chain elongation Diels-Alder ... 

Occurrence, (i-i.-Xylose (11) occurs as a terminal sugar, branching on an l-rhamnan, in the O-chain polysaccharide of the lipopolysaccharide of Xanthomonas... 

Both approaches offer means of obtaining extended-chain unsaturated sugars, branched-chain unsaturated compounds, or C-glycosldes. 

Simple Sugars—Secondary Metabolites Nomenclature 2-Deoxyhexoses 6-Deoxyhexoses Methoxy Sugars Branched-Chain Sugars Sugar Carboxylic Acids Amino Sugars... 

Other unsaturated sugars - Branched chain sugars... 

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