Shikimic Acid Pathway: Phenols

Abstract

Plant metabolites having one or more hydroxyl groups attached to an aromatic ring are known as phenols. Phenols are a heterogeneous group of compounds. One of the most important functions of phenols is in plant communication e.g., allelopathy, attracting pollinating and disseminating agents, attracting symbiotic bacteria, and inhibiting pathogens and predators. Some phenolic compounds (e.g., lignin) are structural components of plant cell wall. Phenols also protect the plant from oxidants and ultraviolet radiation. Due to the free radical scavenging properties, phenolics present in the human diet help to prevent chronic stress related diseases. Most of the phenolic compounds, such as hydroxycinnamic acids, hydroxybenzoic acids, monolignols, lignins, lignans, phenylpropenes, tannins, betalains, and many of the naphthoquinones are produced by the shikimic acid pathway. Some phenolic compounds follow mixed biogenetic pathways. Flavonoids, phlobaphene, curcuminoids, stilbenes and xanthones are produced through formation of polyketides by addition of malonyl-CoA to the phenolic acids. Anthraquinones, some naphthoquinones, benzoquinones and coumarin structures are formed after addition of MVA/MEP pathway derived isopentenyl diphosphate, dimethylallyl diphosphate, geranyl diphosphate or farnesyl diphosphate.