Monosaccharides ring size

The compounds usually known as monosaccharide anhydrides or glycose anhydrides (earlier glycosans ), formation of which involves the anomeric hydroxy group, are named by the same procedure. In these cases the order of preference of ring size designators is pyranose > furanose > septanose. However, three- or four-membered rings should normally be cited as anhydro if there is a choice. 

This is the form employed by the carbohydrate databank CarbBank, and is preferred for most purposes. Each symbol for a monosaccharide unit is preceded by the anomeric descriptor and the configuration symbol. The ring size is indicated by an italic / for furanose or p for pyranose, etc. The locants of the linkage are given in parentheses between the symbols a double-headed arrow indicates a linkage between two anomeric positions. In CarbBank, omission of a/p, D/L, or ftp means that this structural detail is not known. 

Ring fusion methods, 145-146 Ring shape, notation, cyclic monosaccharides, 69 Ring size, cyclic monosaccharides, 59... 

Monosaccharides can differ in their formulas, their ring sizes, and the spatial orientations of their hydroxyl groups. To analyze the differences between two monosaccharides, begin with structural drawings of the molecules, oriented so the ether linkages are in comparable positions. Then examine the stmctures to locate differences in constituents and bond orientations. 

CONVENTIONS FOR INDICATING RING SIZE AND ANOMER CONFIGURATIONS OF MONOSACCHARIDES... 

Table Fl.4.7 contains typical H- H coupling constants for the monosaccharides commonly identified in anthocyanins. When the ring size of the anthocyanin monosaccharides has been reported, all but one have been reported as pyranoses (arabinofuranosyl has been identified in zebrinin Idaka et al., 1987). When examined, the anomeric configurations of the glucosyl, galactosyl, xylosyl and glucuronyl...

Using methods similar to Fischer s, the straight-chain form of any monosaccharide can be worked out. As we have seen, however, monosaccharides exist mostly as cyclic pyra-nose or furanose hemiacetals. These hemiacetals are in equilibrium with the open-chain forms, so sugars can react like hemiacetals or like ketones and aldehydes. How can we freeze this equilibrium and determine the optimum ring size for any given sugar Sir Walter Haworth (inventor of the Haworth projection) used some simple chemistry to determine the pyranose structure of glucose in 1926. 

The Ring Size of Monosaccharide Units and the Position of Linkages... 

Cyclization forms the more stable ring size in a given molecule. The most common monosaccharides, the aldohexoses like glucose, typically form a pyranose ring, so our discussion begins with forming a cyclic hemiacetal from D-glucose. 

Certain monosaccharides— notably aldopentoses and ketohexoses—form furanose rings, not pyranose lii, in solution. The same principles apply to drawing these structures as for drawing pyranose rings, except the ring size is one atom smaller. 

Additionally, H and NMR spectroscopy provide valuable means for ascertaining the ring size and a preferred conformation of functionalized protected monosaccharides such as benzylidene acetals [27,28]. 

We have followed the unraveling of the structure of D-( f )-glucose, and with it structures of the other monosaccharides, to the final working out of the ring size in 1926. Left to be discussed is one aspect whose importance has been realized only since about 1950 conformation. 

The above methodology proved very successful for accessing pure standards of DFAs 5, 7, 10, and 14, which are among the most abundant DFAs in kinetic mixtures of diastereomers as well as in caramel. It is, however, intrinsically limited to compounds having identical ring size at both monosaccharide moieties. Moreover, the di-p-D-fructofuranose l,2 2,l -dianhydride isomer 12 remained elusive. 

In a useful variant of the classical methylation procedure for linkage analysis in the structural determination of oligo- and poly-sacccharides, the fully methylated oligomer is treated with triethylsilane and boron trifluoride etherate or triethylsilane and trimethylsilyl trifluoromethanesulfonate. This procedure produces partially methylated anhydroalditols. These are acetylated and analyzed by GLC-MS.222 223 This reductive-cleavage method makes possible simultaneous determination of identity, ratio, linkage position, and especially the ring size for each monosaccharide component. 

In the second procedure used to determine a monosaccharide s ring size, an acetal of the monosaccharide is oxidized with excess periodic acid. (Recall from Section 20.7 that periodic acid cleaves 1,2-diols.)... 

Solution A trisaccharide is a carbohydrate that consists of three monosaccharides. Hydrolysis breaks the glycosidic bonds between the monosaccharides and we note that D-raffinose is made up of D-glucose, D-galactose and D-fructose. We can determine the ring size and the order of the component sugars by examining the products of D-raffinose s methylation and hydrolysis. These compounds are ... 

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