Furanoses pyranoses

FIGURE 25 5 Distribution of furanose pyranose and open chain forms of d ribose in aqueous solution as mea sured by H and NMR spectroscopy... 

Other alcohols, such as diols [67-69], polyols such as furanoses, pyranoses [70, 71] and polyvinyl alcohol [72] have been reported to enable the reduction of ketones to alcohols. 

As conformational anomeric effects represent only a fraction (—1 to —3 kcal/mol) of the global enthalpic anomeric effect or gem-dioxy stabilizing effect (—6 to —17 kcal/mol), additional factors have to be taken into account. Depending on substitution, steric factors can affect the relative stability of acetal conformers. Dubois et al.2S have demonstrated that in furanose pyranose derivatives a bulky substituent at the furanose... 

Fig. 13 Relative syn position of the two rings in furanose-pyranose structures bearing bulky R substituents.

An increase in solvent polarity further favours the open-chain tautomer in water there is no evidence for any cyclic form [79], This is remarkable in view of the fact that the furanose/pyranose equilibria of sugars, which are interconverted through the open-chain form, are also solvent-dependent [80, 81, 159], Arabinose, for example, in [Dsjpyridine consists of 66 cmol/mol pyranose form (a y9 = 33 33) and 34 cmol/mol furanose form (a y9 = 21 13), compared with 95.5 cmol/mol pyranose form (a y9 = 60 35.5) and 4.5 cmol/mol furanose form (a y9 = 2.5 2.0) in deuterium oxide as solvent [80, 159],... 

Castagnolo D, Botta L, Botta M (2009) One-pot multi-component synthesis of 2, 3-dihy-dropyrans new access to furanose-pyranose 1, 3-C-C-linked-disaccharides. Tetrahedron... 

When a monosaccharide exists in the heterocyclic intramolecular hemiacetal form, the size of the ring is indicated by the suffixes -furanose, -pyranose, and -septanose for five-, six-, and seven-membered rings, respectively. 

The chair DFAs are thermodynamically favored, and can be obtained in good yield if furanose-pyranose interconversion is prevented by protecting groups. Thus, even though compound 10 is a kinetic isomer when considering the whole set of DFAs, it is thermodynamically favored in the difuranose DFA subset. The boat conformers are neither kinetically nor thermodynamically favored. The term... 

The furanose/pyranose ratio can be modified by varying the Si/Al ratio in the MCM-41 used, (Table 9). 

Recall Define the following terms polysaccharide, furanose, pyranose, aldose, ketose, glycosidic hond, oligosaccharide, glycoprotein. 

Grubbs catalyst second-generation XXVin was used in 2009 by Botta and coworkers in a multicomponent procedure for the preparation of 2,3-dihydropyrans (Section 5.3.2.2, Scheme 5.57). As an application of this MCR, furanose-pyranose C—C-linked disaccharide 106 was obtained as a mixture of four diastereoisomers, which after equihbration with ZnClj and hydrogenation afford 107a,b (Scheme 5.80). This reaction constitutes a versatile and effective approach for the preparation of biologically interesting building blocks in carbohydrate chemistry [80]. 

The symbols represent the individual sugars or their residues. The use of the symbol to represent the free sugar is not recommended in textual material. The ring form is indicated by using the first letter of furanose, pyranose, or septanose, itahcised and uncapitalised, added after the abbreviated name of the monosaccharide. No abbreviations are recommended for deoxy sugars, except for deoxyribose which is abbreviated dRib. 

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