OIA2007 PHENYLPROPANOIDS

Phenylpropanoids

Secondary plant metabolites composed of a phenyl ring (C6) and a three-carbon side chain (C3); basic C6–C3 structure.

Precursor amino acids

Phenylalanine and tyrosine via the shikimic acid pathway.

Distribution in plants

Found in all plant tissues: leaves, flowers, fruits, seeds, stems.

Phenolic nature

Contain aromatic rings with hydroxyl groups; classified as phenolics.

Pollinator attraction

Contribute to flower pigmentation (e.g. anthocyanins) to attract pollinators.

UV protection

Block harmful UV radiation, protecting nucleic acids in plant cells.

Light filtering

Allow selective transmission of red and blue-green light for photosynthesis.

Defense role

Reduce palatability, repel herbivores (e.g. caterpillars), and deter microbial pathogens.

Symbiotic interaction

Modulate bacterial/mycorrhizal relationships (promote or inhibit).

Antioxidant role

Prevent cellular aging by scavenging free radicals.

Anti-inflammatory

Reduce inflammation by modulating prostaglandins and cytokines.

Analgesic effects

Alleviate pain through bioactive pathways.

Antiallergic effects

Stabilize mast cells, reducing histamine release.

Vasoprotective

Protect capillaries and blood vessels (↓ fragility, ↓ phlebitis, ↓ edema).

Anticancer properties

Inhibit tumor growth and cancer cell proliferation.

Antioxidant

Scavenge reactive oxygen species (ROS).

Antimicrobial activity

Effective against a variety of microbes.

Gastroprotective

Protect the gastric mucosa and reduce ulcer formation.

Cardioprotective

Improve blood flow, reduce oxidative damage to vessels.

Derived from shikimic acid

Shikimic acid → phenylalanine/tyrosine → phenylpropanoids.

Polyketide pathway

Combines with acetate/malonate derivatives to form flavonoids and related compounds.

Biosynthesis involves

CO₂, H₂O, O₂, monosaccharides, and other metabolic intermediates.

Flavonoid structure

C6–C3–C6 skeleton; subclass of phenylpropanoids.

Flavonoid classification

Flavonols, flavones, flavanones, flavandiols, chalcones, isoflavones, anthocyanidins.

Anthocyanins

Red/blue/purple pigments in flowers and fruits — attract pollinators.

Flavonols/Flavones

Colorless in leaves; regulate light, protect against UV, cause autumn leaf color change.

Isoflavones

Found mainly in legumes; exhibit allelopathy, inhibit herbivory/pathogens.

Coumarin structure

Shikimate-derived lactones with hydroxyl group at C7.

Examples (Coumarin)

Umbelliferone and skimin — UV-absorbing agents (protect skin).

Synthetic derivatives (Coumarin)

Warfarin — an anticoagulant.

Other compounds (Coumarin)

Psoralen and bergapten (furanocoumarins) — used in sunscreens.

Definition (Tannins)

Water-soluble polyphenols with the ability to bind and precipitate proteins.

Industrial use (Tannins)

Used in leather tanning, dyeing, adhesives, and flavoring.

Biological functions (Tannins)

Antiseptic, antioxidant, antimicrobial, aid in hydrogen transfer.

Hydrolysable tannins

Esterified to sugars and release phenolic acids on hydrolysis (e.g. gallic acid, ellagic acid).

Sources of hydrolysable tannins

Clove, rhubarb, chestnut, nutmeg.

Condensed tannins

Not hydrolysable; composed of flavan-3-ol units (e.g. catechin); form phlobaphenes (red pigments).

Sources of condensed tannins

Green tea, cinnamon, cinchona bark.

Examples of catechin structures

(+)-Catechin and flavan-3,4-diol dimers.

Tannin applications

Medicinal (anti-diarrheal, antimicrobial, antioxidant), perfumes, herbicides, metal detox.