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Structures of the three commonly occurring monolignols

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. There are three main monolignols: coniferyl alcohol, sinapyl alcohol and paracoumaryl alcohol. Different plants use different monolignols. For example, Norway spruce lignin is almost entirely coniferyl alcohol while paracoumaryl alcohol is found almost exclusively in grasses.

Monolignols are synthetised in the cytosol as glucosides. The glucose is added to the monolignol to make them water-soluble and to reduce their toxicity. 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.