Coniferyl alcohol, oxidation

It has also been proposed that under the acidic conditions found ia whiskeys, ethanol reacts with lignin (qv) to reduce an alcohol-soluble form of lignin (ethanol lignin). This can be converted into coniferyl alcohol, which can be oxidized to coniferaldehyde. The partial oxidation of ethanol lignin can produce siaapic and coniferyl alcohols that can be converted to syfingaldehyde and vanillin, respectively (8). 

As described above, the enzymatic polymerization of phenols was often carried out in a mixture of a water-miscible organic solvent and a buffer. By adding 2,6-di-0-methyl-(3-cyclodextrin (DM-(3-CD), the enzymatic polymerization of water-insoluble m-substituted phenols proceeded in buffer. The water-soluble complex of the monomer and DM-(3-CD was formed and was polymerized by HRP to give a soluble polymer. In the case of phenol, the polymerization took place in the presence of 2,6-di-O-methyl-a-cyclodextrin (DM-a-CD) in a buffer. Only a catalytic amount of DM-a-CD was necessary to induce the polymerization efficiently. Coniferyl alcohol was oxidatively polymerized in the presence of a-CD in an aqueous solution. ... 

However, in the light of the results presented herein, this cannot be stated unequivocally, otherwise it would follow that only guaiacyl type compounds would be obtained as softwood lignin degradation products. It has been found that the native lignin from the softwood white Scots pine also yields p-hydroxybenzaldehyde upon oxidation. Thus, it seems that either coniferyl alcohol is not the only lignin progenitor in woody tissues, or that this coniferyl compound is preceded in the process of... 

Since the oxidative polymerization of phenols is the industrial process used to produce poly(phenyleneoxide)s (Scheme 4), the application of polymer catalysts may well be of interest. Furthermore, enzymic, oxidative polymerization of phenols is an important pathway in biosynthesis. For example, black pigment of animal kingdom "melanin" is the polymeric product of 2,6-dihydroxyindole which is the oxidative product of tyrosine, catalyzed by copper enzyme "tyrosinase". In plants "lignin" is the natural polymer of phenols, such as coniferyl alcohol 2 and sinapyl alcohol 3. Tyrosinase contains four Cu ions in cataly-tically active site which are considered to act cooperatively. These Cu ions are presumed to be surrounded by the non-polar apoprotein, and their reactivities in substitution and redox reactions are controlled by the environmental protein. 

Condensed Structures in p-Hydroxyphenyl-Guaiacyl Type DHP. It has been difficult to determine the exact amount of p-hydroxyphenylpropane units in lignin. This can best be illustrated by an example nitrobenzene oxidation of a DHP prepared by the Zutropfverfahren method from a mixture of p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol, gave no detectable p-hydroxybenzaldehyde on alkaline nitrobenzene oxidation... 

To determine the reasons for this, DHP s were prepared from a mixture of [ring-2-3H] p-coumaryl alcohol and [or-14C] coniferyl alcohol in the presence of carbohydrates by the procedure described above (35). The LCC fraction so obtained was subjected to combustion, and the exact p-hydroxyphenylpropane guaiacylpropane ratio was determined from the activity of 3H20 and 14C02 released (Figure 2). A portion of the same LCC fraction was also oxidized with nitrobenzene and alkali, and the resulting liberated aromatic aldehydes were then analyzed by HPLC. Results are shown in Table V. 

Figure 2. Dehydrogenative polymerization of a mixture of p-coumaryl alcohol-[ring-2-3H] and coniferyl alcohol-[U-14C], and nitrobenzene oxidation of the DHP to give p-hydroxybenzaldehyde-[ring-2-3H] and vanillin-[formyl-14C].

As can be seen, the molar ratios of p-hydroxyphenyl to guaiacyi units were slightly lower for the DHP s when compared to the original mixtures. This implies that coniferyl alcohol tends to be incorporated into the polymer slightly more readily than p-coumaryl alcohol. On the other hand, the much-reduced ratio of p-hydroxybenzaldehyde to vanillin, liberated during alkaline nitrobenzene oxidation, proved that this DHP contained a larger amount of condensed p-hydroxyphenylpropane units than condensed guaiacyi units. 

Lignin. A polymer found in wood (25—30%). The structure of the lignin monomer is still not completely known. Its similarity to coniferyl alcohol, noted more than 75 years ago (Ref 1), is confirmed by the fact that it can be oxidized to vanillin and hydrogenated to compds of the cyclohexylpropyl type. 

Benzodioxanes (6, 516). The earlier synthesis of benzodioxanes by oxidative coupling of catechol derivatives with methoxypropenylphenols has been extended to the first synthesis of the complex benzodioxane silybin (3) shown in equation (I).2 The starting materials are (2R,3R)-dihydroqucrcctin (I) and coniferyl alcohol (2). In this case, the reaction is not regioselective, 3 and the isomeric 4 being obtained in nearly equal amounts. 

Already in 1897 Klason [52] suggested that gymnosperm lignin is derived from coniferyl alcohol. On the basis of experiments using isoeugenol as a model substance, Erdtman [53] advanced the hypothesis that lignin is a product of the oxidative polymerization of coniferyl alcohol ... 

From a physiological standpoint, molecular and biochemical studies have suggested that ozone stimulates phenolic metabolism and the biosynthesis of lignin or other substances partly derived from coniferyl alcohol [89]. Lignification of mesophyll cell walls might confer some protection against oxidation, and thus be a defence response against ozone [90]. 

Coniferyl alcohol guaiacyl ether (XXXIV) has not yet been isolated from the intermediate mixture, but the presence of an ether of this kind must be concluded from the formation of the acid (IX) on treating lignin with alkali, followed by methylation and oxidation 13). Its origin can be explained by combination of Ra and Rd followed by loss of the side chain of Rd. 

There are cases where the peroxidase is not activated by H202, but by a reaction product instead. Ferrer et al. (1990) described the oxidation of the auxin indole-3-acetic acid (LAA 2.49) and molecular oxygen by a cell wall peroxidase that was able to oxidize coniferyl alcohol (2.48) in the absence of H2C>2. 

Oxidation of IAA (2.49) results in cation 2.50, which undergoes decarboxylation and results in the skatolyl radical (2.51). This compound reacts with molecular oxygen to form peroxyl radical 2.52. With IAA or another cellular reductor, the hydroperoxide 2.53 is formed. It is this compound that activates the peroxidase, and thus allows the oxidation of other substrates, such as coniferyl alcohol. Among the degradation products of 2.53, 3-methylene 2-oxindole (2.54) is the most abundant. 

Ferrer, M. A., Pedreno, M. A., Munoz, R., and Ros Barcelo, A., 1990, Oxidation of coniferyl alcohol by cell wall peroxidases at the expense of indole-3-acetic acid and 02, FEBSLett. 276 127-130. 

Oxidative coupling polymerization provides great utility for the synthesis of high-performance polymers. Oxidative polymerization is also observed in vivo as important biosynthetic processes that, when catalyzed by metalloenzymes, proceed smoothly under an air atmosphere at room temperature. For example, lignin, which composes 30% of wood tissue, is produced by the oxidative polymerization of coniferyl alcohol catalyzed by laccase, an enzyme containing a copper complex as a reactive center. Tyrosine is an a-amino acid and is oxidatively polymerized by tyrosinase (Cu enzyme) to melanin, the black pigment in animals. These reactions proceed efficiently at room temperature in the presence of 02 by means of catalysis by metalloenzymes. Oxidative polymerization is observed in vivo as an important biosynthetic process that proceeds efficiently by oxidases. 

The network structure of lignin, which is made of phenol units, coagulates the cell wall in wood tissue, which is composed of cellulose and hemicellulose. Lignin is currently a waste product because of its complicated structure [1-4], It is produced by an oxidative polymerization of coniferyl alcohol, sinapil alcohol, and cumarol alcohol (Figure 1) catalyzed by metalloenzymes such as laccase and peroxidases. Laccase is a protein whose active center contains four coppers per one subunit [5-20],... 

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