Wood sitosterol

Triterpenoids occur in hardwood parenchyma resin, and closely related sterols are also present in softwoods (Fig. 5-6). Sterols typefied by the abundant /3-sitosterol, mostly have a hydroxyl group in the C-3 position. They also appear as the alcohol component in fatty acid esters (waxes). Triterpenoids and sterols are sparingly soluble substances contributing to pitch problems in pulping and paper making. Some trees contain polyterpenes and their derivatives known as polyprenols. Betulaprenols, present in birch wood, belong to this category of substances (Fig. 5-7). 

Figure 2. Plant sterols found in oil seed, vegetable, and wood sources. Of the more than 40 plant sterols identified, -sitosterol, stigmasterol, and campesterol are the most abundant.

All these lipophilic components perform a function for the living tree. The exact function is not understood for all substances. The composition of the lipophilic wood extractives varies from species to species, and is far from homogeneously distributed in the tree. All woods contain sterols, waxes, glycerides and other aliphatic extractives. However, softwood contains considerable quantities of rosin acids (e.g. abietic acid), but these acids do not exist in hardwood (e.g. birch and aspen). Certain components are predominantly located in the bark of the tree. The sterol fraction from birch and aspen bark comprises almost exclusively beta-sitosterol by way of example. 

Currently apphed processes for the chemical utilization of wood are almost exclusively geared towards chemical pulping. Although, to some extent, the utilization of by-products like vanillin, xylose, furfural, acetic acid or resins (tall oil, rosin and products thereof e.g. sitosterol) see Chapter 9.7) is also included, very often not more than 50% of material utilization is obtained e.g. sulphite mass balance in Figure 9.4.4). 

FIGURE 3.5 Some examples of extractives from wood and non-wood natural fibers (a) Abietic acid (diterpenoids), (b) Limonene (monoterpene), (c) Oleic acid (fatty acids), (d) Sitosteryl 3P-D-glucopyranoside, (e) palmitic acid, (f) octacosanol, (g) octacosanal, and (h) Sitosterol (Marques et. al., 2010). 

In the third phase of the search, a list of all plants in which each compound occurs was requested from NAPRALERT. In this case, the entire database was searched. Printouts were inspected to select only those compounds that occurred in wood or in woody plant parts, and the plants in which the compounds occurred were noted. During this phase of the search, it was noted that compounds (e.g., terpenes) that are components of essential oils or resins were sometimes listed as having been isolated from the wood, and sometimes from the wood essential oil or the resin of a particular species. Thus, for the sake of consistency, plant species in which the compound occurred in the wood essential oil or the resin of conifers were included in the list of plants from which the compound had been isolated. Several compounds that were found to be very widely distributed among woody plants (e.g., yS-sitosterol) were deleted from the analysis at this point for the sake of brevity. Data on the compounds and the plants from which they had been isolated were put into a microcomputer database system and used to construct Table 10.6.3. 

Lovberg, C.-E. (1983) Wood-derived 8-sitosterol - a raw material for the cosmetic industry. Seifen, Oele, Fette, Wachse, 109, 444-445. 

Benzene extracts of leaves, bark and wood were examined. Metabolites identified were of the neolignan, fiavonoid and steroid type. The leaves possess a steroidal fi-action. GC, HPLC and GC-MS studies incficated that it was composed of a mbcture of colesterol, sitosterol, stigmasterol and three other unidentified sterols (7). Four neolignans 8, 9,10 and 2c were also isolated in pure form (8,9). It was shown that compound 10 is produced by dehydration of 9 in acid medium. The substances 8, 9 and 10 were also identified in bark. Wood afforded three fiavonoids (10), a fiavone 11, an a-hydroxydehydrochalcone 12, and a 1,3-diarylpropane 13a, as well as an alkaloid, 3-indolcarboxaldehyde (77). 

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