The Monosaccharide Components

The monosaccharide components will now be discussed. Usually, the component attached directly to the aglycon is of primary interest, because the odd or unusual sugars are almost always found in this place, an exception being D-xylose in the second position in glycoside I of Erysimum cheiranthoides.  

The material of Calotropis latex, according to Hesse and associates, contains no sugar but cychc hydroxy ketones with an ether-like linkage and, sometimes, with an additional thiazoline ring. The direct, acid hydrolysis of these materials is difficult. Pyrolysis or the action of mild alkali produces reductic acid derivatives which are easily identifiable. The investigation of these materials requires special methods.  

To date, the monosaccharides presented in formulas (13)-(42) have been identified in cardiac glycosides. The great majority of these sugars 

The literature references given, except for D-glucose and L-rhamnose, cite, so far as possible, the author who first crystallized or synthesized the sugar in pure, crystalline form. Older literature is usually cited in the references given. Unless otherwise noted, the specific rotations are those for dilute, equilibrated, aqueous solutions at 5892.5 A. 

D-Oleandrose (38) has so far only been isolated from the digitanol glycoside lanafolein, but never from a cardenolide. With the exception of L-acofriose (27), L-acovenose (31), and L-diginose (42), all of these sugars have been prepared synthetically. A glycoside from Beaummtia grandiflora contains L-cymarose, which was recently obtained crystalline. 

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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. 

Many are neutral glucans, being composed of the monosaccharide component... 

Abbreviations for biosynthetic types are composed from abbreviations of nucleoside residues of activated forms of the monosaccharide components. 6 See footnote a to Table VI lin. and br. mean linear and branched polysaccharides. c Including other bacterial amphi-philes of Gram-negative, outer membranes. d Including amphiphiles of Gram-positive cell-membranes. 

Of theoretical and practical value has been the use of anti-carbohydrate antibodies to determine the d or l configurations of monosaccharides. Antibodies generated with the d enantiomer of the sugar in the antigen are inhibited by the d enantiomer of the monosaccharide, but not by the l. The reverse holds for antibodies generated with the l enantiomer of the monosaccharide component in the antigen. Some representative... 

Fig. 3-119. Separation of the monosaccharide components present in glycoprotein hydrolysates. — Separator column CarboPac PA-1 eluent 0.022 mol/L NaOH flow rate 1 mL/min detection pulsed amperometry at a Au working electrode after post-column addition of 0.3 mol/L NaOH injection volume 50 pL solute concentrations 2.5 nmol each of fucose (1), 2-deoxyglucose (2), galactosamine (3), glucosamine (4), galactose (5), glucose (6), and mannose (7) (taken from [111]).

The particular value of acid hydrolysis is that, used in conjunction with paper chromatography, much evidence may be obtained from very small amounts of compound. As the identification of monosaccharides by paper chromatography is well established, the use of this technique in conjunction with total, acid hydrolysis provides a ready means for identifying, both qualitatively and quantitatively, the monosaccharide components of an oligosaccharide. Acid stability of different glycosidic links differs, and total hydrolysis may require from one to four hours at 100° in N acid even more vigorous conditions may be required when amino sugar or uronic acid residues are present. Very rapid hydrolysis in dilute acid,... 

A further investigation was carried out on the EPSs from oleander strain grown on the King s B medium [127], As proved by preliminary results, P. savastanoi in these conditions produces a complex mixture of polysaccharides that were partially purified by gel-filtration chromatography. The main fractions were characterised by chemical and spectroscopic methods. The monosaccharide components were fucose, galactose, N-acetyl-2-deoxy-2-aminogalactose and N-acetyl-2-deoxy-2-... 

Although other differences in peak intensities can be observed for (l->2)-, (l->3)-, and (l- 4)-linked aldosyl-aldoses, the reason for these differences is not yet well understood, but they may also depend on differences in anomeric configuration and in the monosaccharide components. Therefore, at present, authentic reference-materials should be used for establishing these linkage types by m.s. Disaccharides (l->5)- and (l->6)-linked give almost identical spectra typical for these linkages. The formation of typical fragments at m/e 583 (46 and 47) is shown in Scheme 44. 

In the above three formulas the group R represents the alkamine component. The order of attachment of the monosaccharide components was determined by partial and progressive hydrolysis. The pyranose type and the position of coupling of the sugars was determined from the periodic acid oxidation, but the complete structures are not known with certainty. 

Glycosides are compounds in which the substituent is bound to the anomeric carbon. This group comprises numerous natural products the primary metabolites. The most important are nucleosides, the basic structural units from which nucleotides and nucleic acids are formed. The monosaccharide component of the nucleoside is D-ribose or its partially reduced form D-deoxyribose. In biochemistry and molecular biology the most important are the nucleosides in which ribose is bonded to heterocyclic molecules called nucleic bases. The most common nucleic bases are pyrimidines and purines. 

The monosaccharide component of DNA is 2-deoxy-D-ribose (the 2-deoxy refers to the absence of a hydroxyl group at the 2 position), whereas that of RNA is D-ribose. The glycosidic bond is between C-1 (the anomeric carbon) of ribose or 2-deoxyribose and N-1 of a pyrimidine base or N-9 of a purine base. Figure 20.2 shows the structural formula for uridine, a nucleoside derived from ribose and uracil. 

This monosaccharide can be both synthesized by the body and derived from dietary sources (especially from the disaccharide, lactose, where it constitutes one of the monosaccharide components). It is metabolized by the liver to glucose and glycogen. A failure to metabolize galactose occurs in the inborn error ol metabolism, galactosaemia. 

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