phenols

What structural feature defines a phenolic compound?

An aromatic ring with at least one hydroxyl (–OH) group attached.

Are phenolic groups acidic or basic?

Weak acids (pKa ~9–10).

Why are phenolics important in plants?

they function as secondary metabolites involved in defence, pigmentation, structure, and signalling.

Two ways phenolics occur in plants?

As intermediates in metabolic pathways or as secondary metabolites.

What is raspberry ketone used for?

Perfumes, cosmetics, food flavouring; marketed for weight loss (no human evidence)

What is gallic acid?

 A common plant phenolic found in gall nuts, tea, oak bark; part of tannins.

What is capsaicin and where is it concentrated in peppers?

Phenolic compound causing “heat” in chillies; highest in placental tissue.

Why does milk help with chilli burn?

 Casein binds capsaicin and removes it; capsaicin is hydrophobic.

Name 3 medicinal phenolics?

• THC

• L-DOPA

• salicylic acid

• propofol.

What defines a polyphenolic compound?

Contains more than one phenolic unit.

Name three major polyphenolic groups?

• Hydrolysable tannins

• flavonoids

• lignins/condensed tannins.

Common dietary sources of polyphenols?

Tea, berries, wine, cocoa, nuts, coffee, olive oil.

What two sugars feed into the shikimate pathway?

• Erythrose-4-phosphate

• phosphoenolpyruvate (PEP).

 Why is shikimic acid important industrially?

Used to produce antiviral drug Tamiflu.

What does shikimic acid cyclise to produce?

Many phenolic precursors including gallic acid, cinnamic acid, flavonoids.

What is the difference between lignans and lignins?

• Lignans = dimers

• lignins = large polymers.

What reaction forms lignans?

Phenolic oxidative coupling of hydroxycinnamyl alcohols.

Plant role of lignins?

• Strengthen cell walls

• defence (antimicrobial, antifungal, antifeedant).

Medicinal significance of lignans?

Possess antitumour and antiviral activity.

Precursor to coumarins?

Cinnamic acid.

What is dicoumarol and how is it formed?

Anticoagulant produced from spoiled sweet clover.

Which drug did dicoumarol lead to?

warfarin

Mechanism of coumarins?

Inhibit blood clotting (vitamin K antagonists).

What is the basic carbon skeleton of flavonoids?

C₆–C₃–C₆

Give two general health benefits of flavonoids?

Antioxidant activity; protection against CVD and cancers.

What plant functions do flavonoids serve?

Colouration, UV protection, defence.

Basic structure of flavones?

2-phenyl chromen-4-one

How are flavones categorised?

By substitutions at C2 and C3.

Basic structure of isoflavones?

3-phenyl chromen-4-one.

Which plant family produces most isoflavones?

Leguminosae/Fabaceae (beans, soy).

Name two isoflavones?

Genistein and daidzein.

Basic structure of neoflavones?

4-phenylchromen (no OH at position 2).

What is the most common flavan-3-ol in tea?

Catechin

What % of tea leaf dry weight is catechins?

25%

What charge do anthocyanins carry?

positive charge

Difference between anthocyanins and anthocyanidins?

Anthocyanins = glycosides

anthocyanidins = aglycones (no sugar).

What colours do anthocyanins produce?

Red, purple, blue (pH dependent).

What sensory effect do tannins cause?

Astringency (dry, puckering mouthfeel).

Are condensed tannins hydrolysable?

No — linked by strong C–C bonds.

What monomers form condensed tannins?

Catechin units.

What are hydrolysable tannins made of?

A carbohydrate core esterified with phenolic acids (e.g., gallic acid).

What happens during hydrolysis of hydrolysable tannins?

They break into the sugar + phenolic acid.

Basic skeleton of anthraquinones?

Anthracene (three fused rings).

Natural sources of anthraquinones?

Aloe, rhubarb, fungi, lichens.

Common physiological effect of anthraquinones?

Laxative action.

Name a medicinal anthraquinone derivative?

Daunorubicin (anticancer).