Towards lignin-protein crosslinking: Amino acid adducts of a lignin model quinone methide

Brett G. Diehl, Heath D. Watts, James D. Kubicki, Matthew R. Regner, John Ralph, Nicole R. Brown

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

The polyaromatic structure of lignin has long been recognized as a key contributor to the rigidity of plant vascular tissues. Although lignin structure was once conceptualized as a highly networked, heterogeneous, high molecular weight polymer, recent studies have suggested a very different configuration may exist in planta. These findings, coupled with the increasing attention and interest in efficiently utilizing lignocellulosic materials for green materials and energy applications, have renewed interest in lignin chemistry. Here we focus on quinone methides (QMs)-key intermediates in lignin polymerization-that are quenched via reaction with cell-wall-available nucleophiles. Reactions with alcohol and uronic acid groups of hemicelluloses, for example, can lead to lignin-carbohydrate crosslinks. Our work is a first step toward exploring potential QM reactions with nucleophilic groups in cell wall proteins. We conducted a model compound study wherein the lignin model compound guaiacylglycerol-β-guaiacyl ether 1, was converted to its QM 2, then reacted with amino acids bearing nucleophilic side-groups. Yields for the QM-amino acid adducts ranged from quantitative in the case of QM-lysine 3, to zero (no reaction) in the cases of QM-threonine (Thr) 10 and QM-hydroxyproline (Hyp) 11. The structures of the QM-amino acid adducts were confirmed via 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) calculations, thereby extending the lignin NMR database to include amino acid crosslinks. Some of the QM-amino acid adducts formed both syn- and anti-isomers, whereas others favored only one isomer. Because the QM-Thr 10 and QM-Hyp 11 compounds could not be experimentally prepared under conditions described here but could potentially form in vivo, we used DFT to calculate their NMR shifts. Characterization of these model adducts extends the lignin NMR database to aid in the identification of lignin-protein linkages in more complex in vitro and in vivo systems, and may allow for the identification of such linkages in planta.

Original languageEnglish (US)
Pages (from-to)1395-1407
Number of pages13
JournalCellulose
Volume21
Issue number3
DOIs
StatePublished - Jun 2014

Fingerprint

Lignin
Crosslinking
Amino acids
Proteins
Amino Acids
Hydroxyproline
Nuclear magnetic resonance
Isomers
Density functional theory
Threonine
Bearings (structural)
quinone methide
Nucleophiles
Uronic Acids
Carbohydrates
Rigidity
Nuclear magnetic resonance spectroscopy
Ethers
Alcohols
Ether

All Science Journal Classification (ASJC) codes

  • Polymers and Plastics

Cite this

Diehl, Brett G. ; Watts, Heath D. ; Kubicki, James D. ; Regner, Matthew R. ; Ralph, John ; Brown, Nicole R. / Towards lignin-protein crosslinking : Amino acid adducts of a lignin model quinone methide. In: Cellulose. 2014 ; Vol. 21, No. 3. pp. 1395-1407.
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Towards lignin-protein crosslinking : Amino acid adducts of a lignin model quinone methide. / Diehl, Brett G.; Watts, Heath D.; Kubicki, James D.; Regner, Matthew R.; Ralph, John; Brown, Nicole R.

In: Cellulose, Vol. 21, No. 3, 06.2014, p. 1395-1407.

Research output: Contribution to journalArticle

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T1 - Towards lignin-protein crosslinking

T2 - Amino acid adducts of a lignin model quinone methide

AU - Diehl, Brett G.

AU - Watts, Heath D.

AU - Kubicki, James D.

AU - Regner, Matthew R.

AU - Ralph, John

AU - Brown, Nicole R.

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