| Abstract: | The cyclodimerisation of trans-p-coumaric (tCA; (E)-3-(4-hydroxyphenyl) propenoic acid) and trans-ferulic (tFA; (E)-3-(4-hydroxy-3-methoxyphenyl) propenoic acid) acids to form substituted truxillic and truxinic acids has been investigated since dimers of this type are present in graminaceous cell waits and are likely to be of importance in limiting wall biodegradability. Irradiation of a thin film of a mixture of tCA and tF A, under ‘daylight’ fluorescent tubes and incandescent lamps in a growth cabinet, produced three cyclodimers corresponding to 16 % conversion of monomers. Under the same conditions of irradiation, a thin film of FA alone yielded only 2% of F A-F A. When tF A crystals were irradiated, no dimerisation occurred, whereas tCA crystals were totally dimerised to CA-CA. Lower yields of dimers were obtained using UV irradiation. The dimers were shown, by capillary gas-liquid chromatography and mass spectrometry, to be derivatives of truxillic acid (t-2, c-4-diphenyl-r-1, t-3-cyclobutanedicarboxylic acid) composed of CA-CA, CA-FA and FA-FA, and to have gas chromatographic retention times identical to those of dimeric compounds found in grass cell walls. The results are considered in relation to dimerisation of phenolic acids in plant cell walls under the influence of sunlight. |
