OIA2007 W4 MEVALONIC ACID PATHWAY

Secondary Metabolites

Primary classes

Terpenes (Terpenoids) form by isoprene units

Natural unsaturated condensation of products of isoprene units with aliphatic or aromatic properties

What isoprenes?

Isoprene unit: carbon skeleton of isoprene C5H8

*Identify & name isoprene unit types

Joined "head to tail"

What terpenes?

Class of terpenes (example) & sources:

1. Hemiterpenes (C₅)

Isoprene: oaks and poplars (byproduct of photosynthesis)

Prenol (3-methyl-2-buten-1-ol): various fruits (flavorings and fragrances)

2. Monoterpenes (C₁₀)

Menthol: mint/peppermint species such as Mentha arvensis and Mentha piperita.

Camphor: camphor tree wood (Cinnamomum camphora).

α-Phellandrene: essential oils of plants like eucalyptus and ginger.

Citral: Found in lemongrass (Cymbopogon citratus),

3. Sesquiterpenes (C₁₅)

α-Selinene: A major component of celery seed oil.

β-Caryophyllene: Found in clove oil, black pepper, and cannabis.

4. Diterpenes (C₂₀)

Vitamin A (Retinol): dietary β-carotene (carrots, sweet potatoes, and leafy greens)

Gibberellins: Plant hormones first isolated from fungus Gibberella fujikuroi

5. Sesterterpenes (C₂₅)

Scalarane-type sesterterpenoids: marine sponges and shell-less mollusks like nudibranchs. 

6. Triterpenes (C₃₀)

Cholesterol: synthesized in the liver.

Plant-derived: mango, holy basil, ginseng, and horse chestnuts.

7. Tetraterpenes / Carotenoids (C₄₀)

β-Carotene: carrots, sweet potatoes, and leafy greens.

Lycopene: red color of tomatoes, watermelons, and pink grapefruits.

8. Polyterpenes (C₅ₙ)

Natural Rubber (Polyisoprene): latex of the rubber tree (Hevea brasiliensis).

Gutta-percha: latex of Palaquium trees; (dentistry: insulating material)

These terpenoids play diverse roles in nature, including plant defense, pigmentation, and as precursors to vital biological molecules.

Triterpene: four fused rings

*Might ask in MCQ which terpene under which class: sesquiterpenes, a-Selinene & etc.

When join terpenes together, need to identify head & tail

*Redraw structure & identify isoprene units

Terpene synthesis by Mevaloinc Acid Pathway -> product: terpene & steroid

IPP (C5) + DMAP (C5): condensed = C10 Geranyl pyrophospate

IPP (C5) + GPP (C10) - C15 Farnesyl pyrophosphate

2*FPP (C15) - C30 Squalene synthesis

*Provide IPP structure and explain pathway of condensation from C5 - C30

Cholsterol not plant only, but animal & fungal also can

Squalene (squalene epoxidase) -> Squalene epoxide (cyclisation) -> lanosterol/ cycloartenol (demethylation) -> zymosterol (isomerised) -> demosterol (reduction by reductase) -> cholesterol transformation to form various form

MVA pathway -> cholesterol

Mevaloinc acid (MVA)

Phenylpropanoids - Shikimic Acid,

Polyketides (Penicillins) - Acetate,

Steroids - cholesterol syntehsis,

Glycosides - Glycolysis & etc.

Alkaloids - Shikimic & etc.