Benzyl ether LCC linkages

FIGURE 1 Major structural moieties of hemicelluloses, lignin, and LCC linkages. (A) Phenyl glycoside, (B) benzyl ether LCC linkages, (D) p-O-4/a-OH, (O ) P-O /a-OH... 

There is numerous evidence that lignin and polysaccharides are covalently linked, forming manifestations of the so-called lignin-carbohydrate complex (LCC) [2,7,17-19]. In spite of there being relatively low amounts of these linkages in wood [20,21], they play a very important role, as almost all wood lignin is covalently linked to polysaccharides, mainly to hemicelluloses [22]. There are three types of LCC linkages benzyl ether, phenyl... 

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... 

Apphcation of 2D NMR methods overcame this obstacle and elucidated various LCC linkages in preparations isolated from softwoods, HWs, and pulps [21,25,29,48,50,51]. A HSQC correlation 2D NMR technique allowed for the first time direct detection of phenyl glycoside (Structure A, Fig. 1) and benzyl ether (Structure C, Fig. 1) LCC linkages [25,29]. In contrast to the common belief [2,14,17,18], no benzyl ester (a-ester) LCC linkages were detected in these studies. However, y-ester LCC moieties (Structure B, Fig. 1)... 

Signals of LCC benzyl ether of the C2 type are overlapped with a signal of the spirodienone structure (E, Fig. 1). The latter can be quantified from another individual signal and the amount of C2-type LCC linkages can be determined then by the difference [21]. However, considering the relatively low amounts of these structures, this type of quantification should be considered semiquantitative. 

The numbers (5 is the highest, 1 is the lowest) are relative and approximate rather than quantitative. BE, benzyl ether, PhGly, phenyl glycoside LCC linkages. ... 

---