A Biomimetic Route to Lignin Model Compounds <i>via </i>Silver (I) Oxide Oxidation. 1. Synthesis of Dilignols and Non-cyclic Benzyl Aryl Ethers

Quideau, Stéphane; Ralph, John

doi:10.1515/hfsg.1994.48.1.12

Cited by 62 publications

(45 citation statements)

References 51 publications

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“…Yellow needle crystals (55.4 mg, yield 74%) were obtained from acetone-petroleum ether. NMR data were consistent with those reported previously (Quideau and Ralph, 1994;Sy and Brown, 1999).…”

Section: Chemical Synthesis Of Dilignols Trilignols and Tetralignolssupporting

confidence: 91%

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Profiling of Oligolignols Reveals Monolignol Coupling Conditions in Lignifying Poplar Xylem

et al. 2004

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Lignin is an aromatic heteropolymer, abundantly present in the walls of secondary thickened cells. Although much research has been devoted to the structure and composition of the polymer to obtain insight into lignin polymerization, the lowmolecular weight oligolignol fraction has escaped a detailed characterization. This fraction, in contrast to the rather inaccessible polymer, is a simple and accessible model that reveals details about the coupling of monolignols, an issue that has raised considerable controversy over the past years. We have profiled the methanol-soluble oligolignol fraction of poplar (Populus spp.) xylem, a tissue with extensive lignification. Using liquid chromatography-mass spectrometry, chemical synthesis, and nuclear magnetic resonance, we have elucidated the structures of 38 compounds, most of which were dimers, trimers, and tetramers derived from coniferyl alcohol, sinapyl alcohol, their aldehyde analogs, or vanillin. All structures support the recently challenged random chemical coupling hypothesis for lignin polymerization. Importantly, the structures of two oligomers, each containing a g-p-hydroxybenzoylated syringyl unit, strongly suggest that sinapyl p-hydroxybenzoate is an authentic precursor for lignin polymerization in poplar.

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Section: Chemical Synthesis Of Dilignols Trilignols and Tetralignolssupporting

confidence: 91%

“…Compound 2, G(8-5)G, 4-[3-hydroxymethyl-5-(3-hydroxy-propenyl)-7-methoxy-2,3-dihydrobenzofuran-2-yl]-2-methoxy-phenol], (8-5)-dehydrodiconiferyl alcohol, database number 2004: prepared as described previously (Quideau and Ralph, 1994).…”

Section: Chemical Synthesis Of Dilignols Trilignols and Tetralignolsmentioning

confidence: 99%

Profiling of Oligolignols Reveals Monolignol Coupling Conditions in Lignifying Poplar Xylem

et al. 2004

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“…Klason lignin content was used as covariate to adjust means and to increase precision. (Brunow et al 1989 ;Sipila and Brunow 1991a,b,c ;Quideau and Ralph 1994 ;Li and Helm 1995). In contrast, cell wall constituents cannot add to quinone methide intermediates of coniferaldehyde 5 because an a,b-enone structure 6 is formed by loss of the b-H and re-aromatisation (Connors et al 1970) thereby preventing cross-linking of lignin to other wall polymers.…”

Section: Resultsmentioning

confidence: 99%

Severe inhibition of maize wall degradation by synthetic lignins formed with coniferaldehyde

Grabber

Ralph

Hatfield

1998

J. Sci. Food Agric.

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“…Therefore, the peroxidase/hydrogen peroxide (H 2 O 2 ) system, a twostep one-electron transfer system, is commonly used as a biomimetic system for the preparation of dimeric lignin model compounds or dehydrogenation polymers. Oxidative radical coupling using silver (I) oxide (Ag 2 O) as the one-electron oxidant is another convenient approach to the synthesis of lignin model compounds (Zanarotti, 1985;Quideau and Ralph, 1994a). Here, we applied both methods to determine whether tricin is capable of reacting with monolignols under radical coupling conditions and to elucidate the nature of the resulting products.…”

Section: Radical Coupling Reactions Between Tricin and Monolignolsmentioning

confidence: 99%

“…The radical coupling reactions of tricin/sinapyl alcohol (87% overall yield) and tricin/pcoumaryl alcohol (90% overall yield) were carried out via the same method. The oxidation reaction using Ag 2 O was carried out according to the method used in a previous study (Quideau and Ralph, 1994a) with only slight modifications. Tricin (15.7 mg, 47.5 mmol) was dissolved in acetone (5 mL), and Ag 2 O (16.5 mg, 71.3 mmol) was added.…”

Section: Radical Coupling Reaction Between Tricin and Monolignolsmentioning

confidence: 99%

Tricin, a Flavonoid Monomer in Monocot Lignification

et al. 2015

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Tricin was recently discovered in lignin preparations from wheat (Triticum aestivum) straw and subsequently in all monocot samples examined. To provide proof that tricin is involved in lignification and establish the mechanism by which it incorporates into the lignin polymer, the 49-Ob-coupling products of tricin with the monolignols (p-coumaryl, coniferyl, and sinapyl alcohols) were synthesized along with the trimer that would result from its 49-O-b-coupling with sinapyl alcohol and then coniferyl alcohol. Tricin was also found to cross couple with monolignols to form tricin-(49-O-b)-linked dimers in biomimetic oxidations using peroxidase/hydrogen peroxide or silver (I) oxide. Nuclear magnetic resonance characterization of gel permeation chromatography-fractionated acetylated maize (Zea mays) lignin revealed that the tricin moieties are found in even the highest molecular weight fractions, ether linked to lignin units, demonstrating that tricin is indeed incorporated into the lignin polymer. These findings suggest that tricin is fully compatible with lignification reactions, is an authentic lignin monomer, and, because it can only start a lignin chain, functions as a nucleation site for lignification in monocots. This initiation role helps resolve a long-standing dilemma that monocot lignin chains do not appear to be initiated by monolignol homodehydrodimerization as they are in dicots that have similar syringyl-guaiacyl compositions. The term flavonolignin is recommended for the racemic oligomers and polymers of monolignols that start from tricin (or incorporate other flavonoids) in the cell wall, in analogy with the existing term flavonolignan that is used for the lowmolecular mass compounds composed of flavonoid and lignan moieties.Lignin, a complex phenylpropanoid polymer in the plant cell wall, is predominantly deposited in the cell walls of secondary-thickened cells (Vanholme et al., 2010). It is synthesized via oxidative radical coupling reactions from three prototypical monolignols, p-coumaryl, coniferyl, and sinapyl alcohols, differentiated by their degree of methoxylation ortho to the phenolic hydroxyl group. Considered within the context of the entire polymer, the main structural features of lignin can be defined in terms of its p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) units, derived respectively from these three monolignols (Ralph, 2010). Several novel monomers, all deriving from the monolignol biosynthetic pathway, have been found to incorporate into lignin in wild-type and transgenic plants. For example, monolignol acetate, p-hydroxybenzoate, and p-coumarate ester conjugates have all been shown to incorporate into lignin polymers and are the source of naturally acylated lignins (Ralph et al., 2004;Lu and Ralph, 2008); lignins derived solely from caffeyl alcohol were found in the seed coats of both monocot and dicot plants (Chen et al., 2012a(Chen et al., , 2012b; lignins derived solely from 5-hydroxyconiferyl alcohol were found in a cactus (for example, in a member of the genera Astrop...

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A Biomimetic Route to Lignin Model Compounds via Silver (I) Oxide Oxidation. 1. Synthesis of Dilignols and Non-cyclic Benzyl Aryl Ethers

Cited by 62 publications

References 51 publications

Profiling of Oligolignols Reveals Monolignol Coupling Conditions in Lignifying Poplar Xylem

Profiling of Oligolignols Reveals Monolignol Coupling Conditions in Lignifying Poplar Xylem

Severe inhibition of maize wall degradation by synthetic lignins formed with coniferaldehyde

Tricin, a Flavonoid Monomer in Monocot Lignification

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