In our studies (Grabber et al., 2003), nonlignified walls of maize walls were artificially lignified with coniferyl alcohol at pH 4 or 5.5 to vary the propensity of quinone methide intermediates to couple with cell wall constituents (Fig.
Potential cross-linking of pectin to lignin via quinone methide intermediates was also investigated by treating nonlignified walls with pectin methyl esterase (PME) before DHP-CW formation at pH 4 (unpublished data, 2000 and 2003).
Reactivity of secondary hydroxyl groups in methyl [beta]-D-xylopyranoside toward a [beta]-O-4 type quinone methide. J.
Quinone methide intcrmediates formed from lignin during in vitro fermentation of corn stover.
The reactions of a [beta]-O-4-type quinone methide with carboxylic acids in the presence of phenols.
Reactivity of methyl 3-O-([alpha]-L-arabinofuranosyl)-[beta]-D-xylopyranoside and methyl [beta]-D-xylopyranoside towards a [beta]-O-4-quinone methide. J.
Calzada F, Mata R, Lopez R, Linares E, Bye R, Barreto VM, Del Rio F (1991) Friedelanes and triterpenoid quinone methides
from Hippocratea excelsa.
Considering that quinone methides
are the resonance hybrids between the quinoid and benzenoid structures, and their high reactivity to electrophiles and nucleophiles, it is evident that the polycondensation mechanism in all catalytic conditions can be explained by their participation.
"Believing" that pCA is attached at the [Alpha]-carbon suggests that the reaction scheme involves quinone methides
, intermediate products of radical coupling.
Phenolic resin prepared by the reaction of phenols and formaldehyde under alkaline conditions comprises complicated mixtures of mononuclear or polynuclear hydroxymethyl phenols (9, 10) and para-quinone methides (11).
The loss of phenolic hydroxyl functionality may be due to the formation of hemiformals (9, 12) and quinone methides; however, these theories could not be confirmed and need further investigation.
Figueiredo JN, Raz B, Sequin U (1998) Novel quinone methides
from Salacia kraussii with in vitro antimalarial activity.