Monolignols are phytochemicals acting as source materials for biosynthesis of both lignans and lignin. The starting material for production of monolignols is the amino acid phenylalanine. The first reactions in the biosynthesis are shared with the phenylpropanoid pathway, and monolignols are considered to be a part of this group of compounds. Three monolignols predominate: coniferyl alcohol, sinapyl alcohol, and paracoumaryl alcohol. The ratio of these components varies with plant species. For example, Norway spruce lignin is almost entirely coniferyl alcohol, whereas paracoumaryl alcohol is found almost exclusively in grasses.
Monolignols are biosynthetised in the cytosol and linked to glucose, i.e. they are glucosides. The glucosyl group confers water-solublity. The glucosides are transported through the cell membrane to the apoplast. The glucose is then removed and the monolignols are polymerised into lignin.
The phenylpropenes are derived from the monolignols.