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oxidatively coupled ferulates. Carbohydr. Res. 1999, 320, 82–
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(13) Ishii, T. Isolation and characterization of a diferuloyl arabinoxylan
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The main tetramer is likely formed by 4-O-5-coupling of two
preformed 8-5(cyclic)-diferulates. Formation of 4-O-5-linkages
is not favored in the dimerization process of ferulates (38).
However, in analogy to lignin biosynthesis, the formation of a
4-O-5-linkage between preformed dimers is logical; 5-5- and
4-O-5-linkagesinligninpredominantlystemfromoligomer-oligomer
coupling (36). Two ferulate tetramers have been isolated from
corn bran to date (20). Both tetramers contained a central 5-5-
linkage, but both tetramers also contained a 5-5/8-O-4-dehy-
drotriferulate moiety, probably the predominant trimer in corn
bran. Therefore, it was hard to deduce whether those tetramers
were formed by coupling of a fourth unit to a preformed trimer
or whether two preformed dimers were coupled by the formation
of a 5-5-linkage. In our model system the dominant tetramer
most likely stems from 4-O-5-coupling of two dimers, possibly
giving a hint that also the corn bran tetramers were formed by
5-5-dimer-dimer coupling. Whereas a trimer analogous to
compound 1 was already isolated from a natural source, the
race will now be to isolate or identify a tetramer analogous to
compound 2 from a natural source.
(14) Bunzel, M.; Allerdings, E.; Ralph, J.; Steinhart, H. Cross-linking
of arabinoxylans via 8-8-coupled diferulates as demonstrated by
isolation and identification of diarabinosyl 8-8(cyclic)-dehy-
drodiferulate from maize bran. J. Cereal Sci. 2008, 47, 29–40.
(15) Funk, C.; Ralph, J.; Steinhart, H.; Bunzel, M. Isolation and
structural characterisation of 8-O-4/8-O-4- and 8-8/8-O-4-coupled
dehydrotriferulic acids from maize bran. Phytochemistry 2005,
66, 363–371.
(16) Bunzel, M.; Ralph, J.; Funk, C.; Steinhart, H. Structural elucidation
of new ferulic acid-containing phenolic dimers and trimers isolated
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ferulic acid from maize bran. Phytochemistry 2003, 63, 899–903.
(19) Bunzel, M.; Ralph, J.; Funk, C.; Steinhart, H. Isolation and
identification of a ferulic acid dehydrotrimer from saponified maize
bran insoluble fiber. Eur. Food Res. Technol. 2003, 217, 128–
133.
(20) Bunzel, M.; Ralph, J.; Bru¨ning, P.; Steinhart, H. Structural
identification of dehydrotriferulic and dehydrotetraferulic acids
from insoluble maize bran fiber. J. Agric. Food Chem. 2006, 54,
6409–6418.
(21) Carvajal-Millan, E.; Landillon, V.; Morel, M.-H.; Rouau, X.;
Doublier, J.-L.; Micard, V. Arabinoxylan gels: Impact of the
feruloylation degree on their structure and properties. Biomacro-
molecules 2005, 6, 309–317.
(22) Ralph, J.; Helm, R. F.; Quideau, S. Lignin-feruloyl ester cross-
links in grasses. Part 2. Model compound syntheses. J. Chem.
Soc., Perkin Trans. 1 1992, 2971–2980.
(23) Quideau, S.; Ralph, J. A biomimetic route to lignin model
compounds Via silver(I) oxide oxidation. 1. Synthesis of dilignols
and non-cyclic benzyl aryl ethers. Holzforschung 1994, 48, 12–
22.
(24) Ralph, J.; Garcia-Conesa, M. T.; Williamson, G. Simple prepara-
tion of 8-5-coupled diferulate. J. Agric. Food Chem. 1998, 46,
2531–2532.
(25) Liu, H.-L.; Wan, X.; Huang, X.-F.; Kong, L.-Y. Biotransformation
of sinapic acid catalyzed by Momordica charantia peroxidase. J.
Agric. Food Chem. 2007, 55, 1003–1008.
(26) Monien, B. H.; Henry, B. L.; Raghuraman, A.; Hindle, M.; Desai,
U. R. Novel chemo-enzymatic oligomers of cinnamic acids as
direct and indirect inhibitors of coagulation proteinases. Bioorg.
Med. Chem. 2006, 14, 7988–7998.
(27) Liu, H.-L.; Kong, L.-Y.; Takaya, Y.; Niwa, M. Biotransformation
of ferulic acid into two new dihydrotrimers by Momordica
charantia peroxidase. Chem. Pharm. Bull. 2005, 53, 816–819.
(28) Ward, G.; Hadar, Y.; Bilkis, I.; Konstantinovsky, L.; Dosoretz,
C. G. Initial steps of ferulic acid polymerization by lignin
peroxidase. J. Biol. Chem. 2001, 276, 18734–18741.
(29) Mu¨nzenberger, B.; Hammer, E.; Wray, V.; Schauer, F.; Schmidt,
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ABBREVIATIONS USED
DAD, diode array detector; SEC, size exclusion chromatog-
raphy; THF, tetrahydrofuran.
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