sinapylalkohol

Sinapyl alcohol is a cinnamyl alcohol and one of the three primary monolignols that are incorporated into lignin in vascular plants. It represents the syringyl-type unit of lignin, distinguished by a benzene ring bearing two methoxy groups at the 3 and 5 positions and a hydroxy group at the 4 position, linked to a three-carbon side chain. Through radical coupling catalyzed by peroxidases and laccases, sinapyl alcohol units are polymerized to form the lignin network in plant cell walls.

In plant metabolism, sinapyl alcohol is produced via the phenylpropanoid pathway from phenylalanine, with enzymes such as phenylalanine ammonia-lyase and various O-methyltransferases contributing to the introduction of methoxy groups. It acts as a precursor to syringyl lignin units, which co-exist with guaiacyl and, in some taxa, p-hydroxyphenyl units in lignin. The relative abundance of syringyl units varies by species, with hardwoods typically showing higher S content, softwoods being richer in G units, and grasses presenting mixed compositions.

The composition of lignin, including the amount of syringyl units, influences plant cell-wall properties and industrial processing. Lignin rich in syringyl units is often associated with a less condensed structure and greater susceptibility to certain chemical treatments, affecting pulping, enzymatic digestion, and biofuel production. Sinapyl alcohol thus plays a central role both in plant biology and in the industrial utilization of lignin-containing biomass.