Submitted to: Tetrahedron
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 11, 1997
Publication Date: N/A
Interpretive Summary: A major component in all terrestrial plants, lignin is a polymer that limits digestion of plants by animals and must be removed from wood to make paper. One of its building blocks, trans-coniferyl alcohol, has been known for a long time. But there is another form of coniferyl alcohol, cis- coniferyl alcohol. Although this form can be found in some plants, it is not known whether lignin is made from it in plants. We have examined the production of lignin from cis-coniferyl alcohol to see if it forms the same lignin units. Basically, it does, but there are some new or different units that should eventually help us to determine whether plants utilize cis- coniferyl alcohol to make their lignin. Understanding this process is more important now as plants are being biogenetically engineered to allow them to be better utilized. Such studies are at the heart of efforts to improve agricultural sustainability and maximize our plant resources.
Technical Abstract: The (Z)-monolignols (hydroxycinnamyl alcohols) are found along with their predominant (E)-isomers in a number of plants. Their role in lignification is unknown. A new synthetic route to (Z)-coniferyl alcohol has been developed via Still and Gennari's modification of the Horner-Emmons olefination to produce (Z)-unsaturated esters. Although previous studies have shown that (Z)-coniferyl alcohol will polymerize by single-electron (radical) processes to produce synthetic lignins, the stereochemistry of units in the resulting structure had not been addressed. NMR analysis of a synthetic lignin from (Z)-coniferyl alcohol indicates that unsaturated sidechains in the resulting lignin retain their (Z)-geometry. Other structures are altered in their relative proportions but retain the same stereochemistry. Assignment of structures in these synthetic lignins provides the necessary database for more careful examination of real plant lignins.