Pinoresinol structures, being important components of softwood lignin, are readily detected by NMR. They escaped detection from β-ether cleaving degradation analysis presumably due to linkage at their 5-positions in 5-5- or 4-O-5linked units. In this study, new lignin model compounds related to such pinoresinol structures have been synthesized via a peroxidase-catalyzed H2O2 oxidative coupling reaction using 5-5- or 4-O-5-linked coniferyl alcohol (proposed intermediates) and coniferyl alcohol (CA). It was found that 5-5- or 4-O-5-linked coniferyl alcohol can cross-couple with CA producing pinoresinols in addition to other homo- and cross-coupled products. A total of seven new model compounds have been obtained and characterized by NMR. Based on NMR data of these model compounds, it was demonstrated that 5-5-linked pinoresinol and 4O-5-linked pinoresinol models could be differentiated in HMBC spectra. With appropriate modification (etherification) to the model compounds obtained in this study, it is likely t hat 5-5- or 4-O-5-linked pinoresinol structures in softwood lignin can be identified.
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