cis-p-Coumarates acylate the lignin sidechain in grasses and other plants

10 páginas- 5 figuras.- 2 tablas.- referencias.-

In this study, we present evidence that the lignins of grasses and other plants undergo partial acylation by cis-p-coumarate. Unlike the more widely observed trans-p-coumarates, cis-p-coumarates represent a novel acylation pattern on the lignin sidechains. The finding was substantiated by detailed NMR analyses (HSQC, HSQC-TOCSY, HMBC) and alkaline hydrolysis of the lignin isolated from abacá, a plant that exhibits substantial amounts of cis-p-coumarate. The presence of cis-p-coumarates broadens the range of groups known to acylate lignin sidechains and suggests that subtle variations in the acylation pattern can modulate the final structure and properties of the lignin. A broad survey of lignins from diverse plant species revealed that all lignins incorporating trans-p-coumarates also incorporated cis-p-coumarates, albeit in varying proportions. The cis-p-coumarate content ranged from 2 % to 12 % of the total p-coumarate units, depending on the plant species. As cis-p-coumarate is formed through the isomerization of trans-p-coumarate triggered by UV light, this transformation may occur at various stages, including at the free p-coumaric acid level, at the monolignol p-coumarate level, or directly within the lignin polymer. The potential pathways through which cis-p-coumaric acid becomes incorporated into the lignin are discussed.

This work was financed by MCIN/AEI/10.13039/501100011033 (project PID2023–152543OB-I00) co-financed by the European Regional Development Fund (ERDF) “A way to make Europe”. J. Ralph was supported by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, Biological and Environmental Research Program under Award Number DE-SC0018409.

Peer reviewed