Branched monosaccharides

Several branched monosaccharides have trivial names, some established by long usage. Examples are given below, together with systematic names for the (cyclic or acyclic) forms illustrated. (See also the alphabetical listing of trivial names in the Appendix.) Enantiomers of the sugars listed should be named systematically. 

If the branched monosaccharide forms a cyclic hemiacetal or hemiketal, the chain which includes the ring atoms rather than any alternative open chain must be the basis of the name. Otherwise the parent is chosen according to the principles given in 2-Carb-2.1. 

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. " ... 

Lubineau reported a series of research works on the preparation of C-branched monosaccharides and C-disaccharides under indium promoted Barbier-type allylation in aqueous media [49]. In the case of substrate 97, the reaction, which took place in H20/Et0H (1 2) at 50 °C, gave unique stereoisomer 98 with complete regio- and diastereoselectivity. From... 

D-Apiose a branched monosaccharide, M, 150.13, Kd +9° (pure syrup). d-A. is found in various glyco-... 

Branched monosaccharides are treated according to the afore-stated principles as substituted unbranched sugars, with customary trivial names... 

FIGURE 7.21 Amylose and amylopectin are the two forms of starch. Note that the linear linkages are o (1 4), but the branches in amylopectin are o (1 6). Branches in polysaccharides can involve any of the hydroxyl groups on the monosaccharide components. Amylopectin is a highly branched structure, with branches occurring every 12 to 30 residues. 

Branchand and coworkers have used cobriloximes as alkyl rathcM precursors for the cross-conphng reacdon v/ith rutronates." This method Is very useful for producing branched-chain monosaccharides, as shovm in Eq. 5.39." ... 

This is a modified form of the 1980 recommendations [4]. Priority is now given to naming cyclic forms, since in most cases branched-chain monosaccharides will form cyclic hemiacetals or hemiketals. 

A branched-chain monosaccharide is named as a substituted parent unbranched monosaccharide, as outlined in 2-Carb-16.1 to 2-Carb-16.4. 

Chart V. Choice of parent in branched-chain monosaccharides. In the first names given for examples 1,3 and 4, side-chain configuration is specified by use of R and S. This approach is generally preferred in all but the simplest cases, as less open to misinterpretation. 

IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN), Nomenclature of branched-chain monosaccharides (Recommendations 1980), Eur. J. Biochem., 119, 5-8... 

This group includes a set of anionic polysaccharides secreted by unrelated bacteria. The common theme, however, is that their main chains have the same tetrasaccharide repeat. Although (high acyl) native gellan (42) and (deacylated) gellan (40,41) are linear polymers, welan (43) is a branched polymer in which a monosaccharide side chain is regularly attached to each repeat. Other members of this family, such as S-657 and rhamsan, are also branched, like welan."0... 

Polysaccharides are condensation products of more than ten monosaccharide units examples are the starches and dextrins, which may be linear or branched polymers. Polysaccharides are sometimes classified as hexosans or pentosans, depending upon the identity of the constituent monosaccharides. 

Rhamnogalacturonan 11 (RG-11) is a structurally complex, pectic polysaccharide that is present in the primary cell-walls of higher plants. It is composed of 60 glycosyl residues, and is a very complex molecule indeed. For example, on acid hydrolysis, at least ten different monosaccharides are formed, including the novel aceric acid (30), which is the only branched-... 

A further complication that may be encountered in the nomenclature of branched-chain monosaccharides is in the numbering of the carbon atoms of the molecule. There is some precedent for numbering the carbon atoms of the branched moiety continuously with the carbon atoms of the main chain. However, this can result in confusion and ambiguity, especially when there are further substituents on the branched carbon atoms. In this connection, the Geneva system of nomenclature11 provides a reasonable solution, which is illustrated in the naming of compounds XII10 and XIII. 

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