Carbohydrate linkage sites

Different degradation techniques are commonly used for the analysis of LCC isolated from plant tissues. This approach includes cleavage of lignin-carbohydrate bonds and identification of the resulting products by way of alkaline hydrolysis (saponification) [20], acid hydrolysis [36,66], Smith degradation [67], ozonolysis [68], methylation analysis [69-72], and DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone) oxidation [18,73-76]. The two last techniques are the most common for the analysis of carbohydrate linkage sites in LCC preparations. 

As it has been shown earlier, the quantification of LCC linkages with traditional wet chemistry methods is limited mostly to relative quantification of carbohydrate sites linked to lignin. In contrast, our quantitative 2D NMR approach [21] allows for quantification of lignin sites involved in LCC linkages of different types. However, it does not provide information on the specific carbohydrate linkage sites yet. Therefore, a combination of quantitative NMR analysis and appropriate wet chemistry methods, such as a routine carbohydrate analysis, along with the methylation and DDQ oxidation degradation techniques, could be the best approach for comprehensive LCC analysis. 

Scheme 1. Estimation of linkage sites in lignin-carbohydrate moieities.

The DDQ oxidation technique identifies only the linkage sites of carbohydrates involved in benzyl ether-type LCC bonds (Fig. 5) [18,73-76]. Briefly, an LCC preparation is thoroughly acetylated, then subjected to DDQ oxidation to induce the oxidative cleavage of LCC bonds of the benzyl ether type into the corresponding a-carbonyl in acetylated lignin and terminal hydroxyl groups in acetylated carbohydrate moieties, respectively. The resulting carbohydrate mixture is then methylated by Prehm s procedure and hydrolyzed... 

An example of the use of Smith degradation for carbohydrate sequencing is a study on the sites of AcNeu-Gal-GlcNAc linkages to... 

---