Radical formation and coupling of hydroxycinnamic acids containing 1,2-dihydroxy substituents

Wendy Roslyn Russell, Mark Burkitt, Lorraine Scobbie, Andrew Chesson

Research output: Contribution to journalArticle

11 Citations (Scopus)

Abstract

Hydroxycinnamic acids involved in the deposition and cross-linking of plant cell-wall polymers do not usually contain 1,2-dihydroxy substituents, despite the presence of both 3,4-dihydroxycinnamic acid and 4,5-dihydroxy-3-methoxycinnamic acid as intermediates in the biogenesis of lignin. Since the O-methyl transferases, enzymes catalysing methylation, are targets for the genetic manipulation of lignin biosynthesis, the potential incorporation of these 1,2-dihydroxated substrates becomes increasingly significant. Using EPR spectroscopy, it was observed that 1,2-dihydroxy substituents did not have an inhibitory effect on radical formation. Increasing the extent of hydroxylation and methoxylation, resulted in an increased ease of substrate oxidation. Despite formation of the parent radicals, coupling did not proceed, under conditions that generally result in phenylpropanoid polymerisation. It is postulated that intermolecular radical-coupling reactions are inhibited due to rapid conversion to the o-quinone. In contrast, when methoxylated at C3, as in 4,5-dihydroxy-3-methoxycinnamic acid, radical coupling proceeds with the major product resulting from 8-O-3 radical coupling and formation of a substituted 2,3-dihydro-1,4-dioxin ring.

Original languageEnglish
Pages (from-to)206-215
Number of pages10
JournalBioorganic Chemistry
Volume31
Issue number3
Early online date28 May 2003
DOIs
Publication statusPublished - Jun 2003

Fingerprint

Coumaric Acids
Lignin
Hydroxylation
Acids
Methylation
Biosynthesis
Plant Cells
Substrates
Transferases
Polymerization
Cell Wall
Paramagnetic resonance
Spectrum Analysis
Polymers
Spectroscopy
Oxidation
Enzymes
benzoquinone
caffeic acid
1,4-dioxin

Keywords

  • Hydroxycinnamic acid
  • EPR
  • O-Methyl transferase
  • Lignin biosynthesis
  • Caffeic acid
  • Catechol

Cite this

Radical formation and coupling of hydroxycinnamic acids containing 1,2-dihydroxy substituents. / Russell, Wendy Roslyn; Burkitt, Mark; Scobbie, Lorraine; Chesson, Andrew.

In: Bioorganic Chemistry, Vol. 31, No. 3, 06.2003, p. 206-215.

Research output: Contribution to journalArticle

Russell, Wendy Roslyn ; Burkitt, Mark ; Scobbie, Lorraine ; Chesson, Andrew. / Radical formation and coupling of hydroxycinnamic acids containing 1,2-dihydroxy substituents. In: Bioorganic Chemistry. 2003 ; Vol. 31, No. 3. pp. 206-215.
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AB - Hydroxycinnamic acids involved in the deposition and cross-linking of plant cell-wall polymers do not usually contain 1,2-dihydroxy substituents, despite the presence of both 3,4-dihydroxycinnamic acid and 4,5-dihydroxy-3-methoxycinnamic acid as intermediates in the biogenesis of lignin. Since the O-methyl transferases, enzymes catalysing methylation, are targets for the genetic manipulation of lignin biosynthesis, the potential incorporation of these 1,2-dihydroxated substrates becomes increasingly significant. Using EPR spectroscopy, it was observed that 1,2-dihydroxy substituents did not have an inhibitory effect on radical formation. Increasing the extent of hydroxylation and methoxylation, resulted in an increased ease of substrate oxidation. Despite formation of the parent radicals, coupling did not proceed, under conditions that generally result in phenylpropanoid polymerisation. It is postulated that intermolecular radical-coupling reactions are inhibited due to rapid conversion to the o-quinone. In contrast, when methoxylated at C3, as in 4,5-dihydroxy-3-methoxycinnamic acid, radical coupling proceeds with the major product resulting from 8-O-3 radical coupling and formation of a substituted 2,3-dihydro-1,4-dioxin ring.

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