Rhamnogalacturonan ferulic acid

In many plant species, the 05 of ot-L-Ara/ residues in plant cells walls is esterified with ferulic acid. One-electron oxidation results in cross-linking, both of feruloylated polysaccharides to each other, as with the terminal ot-L-Ara/ residues esterified with ferulic acid in the arabinan of rhamnogalacturonan 1 and to lignin (Figure 4.62). 

Figure 4. (A). A partial structure of homogalacturonan. In primary walls between 50 and 80% of the GalpA are esterified. (B). A partial structure of rhamnogalacturonan I (1) the backbone of RG-I is composed of the disaccharide repeating unit — 4)-a-D-GalpA-(l— 2)-a-L-Rhap-(l—The GalpA residues are often O-acetylated. Some of the rhamnosyl residues are substituted at C-4 with oligosaccharides composed predominantly of Ara/ and Galp residues (2 and 3). Some side chains contain (4-0-Me)GlcpA (4). In the Chenopodiaceae, the side chains are esterified with phenolic acids such as ferulic acid (5). Oxidative coupling of the phenolic acids may be a way in which pectins are cross-linked.

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