Methyl esterified residues

Next to the subunit from which these oligomers were released, two other subunits were recognized a highly methyl esterified xylogalacturonan segment and residual stubs of the backbone rich in branched arabinose side chains. 

The methyl ester of operculinic acid E was obtained by basic hydrolysis and methylation of the crude resin glycoside mixture of 7. murucoides. Mumcoidins XII (53) and XIII (54) afford operculinic acid E as their oligosaccharide core. The lactonization site was placed at C-3 of the first rhamnose unit. These resin glycosides contain an esterifying residue that is composed of n-dodecanoic or (25)-methylbu-tyric acids at the C-2 or C-3 positions on the second rhamnose unit of the oligosaccharide core and (25)-methylbutyric acid at C-4 on the third rhamnose (30). 

L-rliamnopvranosyl residue D-galactopyranosyluronic acid residue methyl-esterified D-galactopyranosyluronic acid residue... 

In potato pectic polysaccharides, the RG-I domain accounts for 75% of the total, a much higher proportion than in pectic polysaccharides of other species ( 20-35%) (Oomen et al., 2003 Mohnen et al., 2008). RG-1 consists of a backbone of alternating a-D-galacturonic acid and a-L-rhamnosyl residues, linked as indicated in Figure 3.3, which in potato accounts for 14% of the total RG-1 (Oomen et al., 2003). Although the galacturonic acid residues are probably not methyl-esterified, they may be acetylated. This is so in potato, where a preparation... 

D-Galacturonic acid residues, partially methyl esterified presence of 1,2-linked L-rhamnosyl residues... 

Pectin consists predominantly of sequences of galacturonic acid residues (which are quite similar to the G units in alginate), with occasional interruptions by rhamnose residues. At least some of the carboxyl groups are methyl esterified, the precise distribution depending upon the plant source and age, and an important aspect still not fully understood. Reasonably in view of their structural similarity, pectins of low degree of esterification behave like alginates, and gel with divalent ions. The more esterified materials gel under conditions of low pH and decreased water activity, Le. where intermolecular electrostatic repulsions are reduced in this case the junction zones are thermoreversible at, say, 40 C. 

Pectins are important in cell wall assembly and detailed information of their structure will help to elucidate the relationship between the structures and physical properties. One possible approach is the chemical degradation of pectins. The specific degradation of the methyl esterified galacturonic acid residues of pectin to the corresponding... 

Needs, P. W., Rigby, N. M., Ring, S. G., MacDougall, A. J. Specific degradation of pectins via a carbodiimide-mediated Lessen rearrangement of methyl esterified galacturonic acid residues. Carbohydr. Res. 2001, 333,47-58. 

Pectic acid, pectin D-GalA L-Rha L-Ara D-Gal a-(l— 4)-linked D-GalpA (or methyl esterified GalpA) residues containing (1— 2)-linked B-L-Rha/> short arabinan and galactan side chains linked to C-4 of Rhap... 

Hakomori methylation of polysaccharides containing uronic acid residues results in their complete esterification. The ester group in the esterified residue (A in 12) is electron-withdrawing, allowing the hydrogen attached to C5 to become sufficiently acidic that on treatment with base it is eliminated giving the 4,5-unsaturated residue (B in 12). If the uronic acid is 4-linked, the substituent at C-4 is eliminated (Lindberg et al., 1975). 

Scheme 4.,32 Carhndiimide-mediated Lossen rearrangement of methyl-esterified galactnrnnic acid residues.

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