PREPARATION OF SYNTHETIC LIGNINS WITH SUPERIOR NMR CHARACTERISTICS VIA ISOTOPICALLY LABELED MONOLIGNOLS

Synthetic lignins are particularly valuable for studying aspects of li gnification, plant cell wall cross-linking, and lignin structure. If t hey are not too highly polymeric, they are soluble in normal Lignin so lvents and amenable to solution-state NMR studies. However, in the app lication of inverse-detected correlation experiments, particularly the popular HMQC and HMBC experiments, the spectra have annoying T-1-nois e ridges. These artifacts make it difficult to locate correlation peak s that are near the methoxy signal in the proton dimension. One soluti on is to use gradient-enhanced NMR but that requires additional hardwa re that is not yet ubiquitous. An alternative is to produce monolignol s in which the atoms of the methoxy group are NMR-invisible. We have a ccomplished this by preparing coniferyl and sinapyl alcohols using C-1 3-depleted deuterated methyl iodide ((C2H3I)-C-12). The methods, which incorporate steps simpler than have been used previously for labeled monolignols, are sufficiently low cost and straightforward that these monomers can be utilized for any synthetic lignins destined for NMR st udies. The NMR spectra of lignins derived from these 'methoxy-less' mo nomers are markedly superior to their normal-monomer counterparts. Sev eral popular NMR experiments are illustrated for synthetic lignins der ived from normal vs. isotopically labeled coniferyl alcohol, along wit h some useful experiments that have not been seen in lignin-related pu blications to date.