ANWSER
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Question 1:
(a) List Five classes of terpenoids:
1. Monoterpenoids (C10)
2. Sesquiterpenoids (C15)
3. Diterpenoids (C20)
4. Triterpenoids (C30)
5. Tetraterpenoids (C40)
(b) State the precursor required for the biosynthesis of each class:
1. Monoterpenoids: Geranyl pyrophosphate (GPP)
2. Sesquiterpenoids: Farnesyl pyrophosphate (FPP)
3. Diterpenoids: Geranylgeranyl pyrophosphate (GGPP)
4. Triterpenoids: Squalene
5. Tetraterpenoids: Phytoene
(c) Assign the precursor for the biosynthesis of the listed terpenoids:
(i) Myrcene: GPP
(ii) Humulene: FPP
(iii) Bisabolene: FPP
(iv) Ξ³-terpinene: GPP
(v) Ξ±-terpineol: GPP
(vi) Ξ±-Phellandrene: GPP
(vii) Squalene: Squalene (from FPP)
(viii) Germacrene A: FPP
(ix) Lanosterol: Squalene
(x) Thymol: GPP
(d) Use suitable chemical equations to illustrate the biosynthesis of a terpenoid:
Example: Biosynthesis of Myrcene from GPP
GPP β Linalyl pyrophosphate β Myrcene (via elimination of pyrophosphate and rearrangement).
(e) Class of terpenoids that predominate in essential oils:
Monoterpenoids and Sesquiterpenoids.
(f) Five methods to extract essential oils from plant material:
1. Steam distillation
2. Solvent extraction
3. Cold pressing
4. Supercritical fluid extraction (CO2)
5. Enfleurage
(g) Procedure for steam distillation:
1. Place plant material in a distillation apparatus.
2. Pass steam through the material to vaporize the essential oils.
3. Condense the vapor mixture (oil + water) in a condenser.
4. Separate the oil from the water using a separatory funnel.
(h) Instrumental technique to establish terpenoids in essential oils:
Gas Chromatography-Mass Spectrometry (GC-MS).
(i) Principle of GC-MS:
GC separates the components of a mixture based on their volatility and affinity to the stationary phase, while MS identifies and quantifies the compounds by their mass-to-charge ratio (m/z).
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Question 2:
(a) Precursors for prostaglandin biosynthesis:
1. Arachidonic acid (20:4, Ο-6) β Prostaglandin series (e.g., PGE2, PGF2Ξ±).
2. Eicosapentaenoic acid (EPA, 20:5, Ο-3) β Prostaglandin series (e.g., PGE3).
(b) Series of prostaglandins from precursors:
– Arachidonic acid: Series 2 (e.g., PGE2).
– EPA: Series 3 (e.g., PGE3).
(c) Prostanoic acid skeleton for each series:
Prostanoic acid skeleton: 20-carbon carboxylic acid with a 5-membered ring (cyclopentane) and two side chains.
(d) Five classes of prostaglandins:
1. PGA (e.g., PGA1)
2. PGB (e.g., PGB1)
3. PGD (e.g., PGD2)
4. PGE (e.g., PGE2)
5. PGF (e.g., PGF2Ξ±)
(e) Structure of one prostaglandin from each class:
– PGE2: Cyclopentane ring with hydroxyl at C9, keto at C11, and double bonds at C5, C13.
– PGF2Ξ±: Similar to PGE2 but with hydroxyl at C9 and C11.
(f) Prostaglandins used as drugs in obstetrics:
1. Dinoprostone (PGE2) β Induces labor.
2. Misoprostol (PGE1 analog) β Prevents ulcers, induces labor.
3. Carboprost (15-methyl-PGF2Ξ±) β Controls postpartum hemorrhage.
(g) Applications:
– Dinoprostone: Cervical ripening and labor induction.
– Misoprostol: Labor induction and abortion.
– Carboprost: Treats postpartum bleeding.
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Question 3:
(a) Four classes of steroidal hormones:
1. Glucocorticoids (e.g., Cortisol)
2. Mineralocorticoids (e.g., Aldosterone)
3. Androgens (e.g., Testosterone)
4. Estrogens (e.g., Estradiol)
(b) Name and structure of one compound per class:
– Cortisol: 21-carbon steroid with hydroxyl at C17, keto at C3, C20.
– Aldosterone: Similar to cortisol with aldehyde at C18.
– Testosterone: 19-carbon steroid with keto at C3, hydroxyl at C17.
– Estradiol: 18-carbon steroid with aromatic A-ring, hydroxyl at C3, C17.
(c) Hydrocarbon skeleton for nomenclature:
– Gonane (for estrogens).
– Estrane (for estradiol).
– Androstane (for testosterone).
– Pregnane (for cortisol, aldosterone).
(d) Structure of hydrocarbon skeletons:
– Gonane: Tetracyclic (no C19 methyl).
– Pregnane: 21-carbon skeleton (C20, C21 side chain).
(e) Common hydrocarbon skeleton:
Cyclopentanoperhydrophenanthrene (sterane).
(f) Significance of steroidal hormones:
– Cortisol: Regulates metabolism and immune response.
– Aldosterone: Controls electrolyte balance.
– Testosterone: Male sexual development.
– Estradiol: Female sexual development.
(g) Spectroscopic techniques:
1. Infrared Spectroscopy (IR).
2. Nuclear Magnetic Resonance (NMR).
(h) Principle of techniques:
– IR: Measures vibrational transitions of functional groups (e.g., OH, C=O).
– NMR: Detects nuclear spin transitions in a magnetic field (e.g., 1H, 13C).
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Question 4:
(a) Roles in plants:
– Alkaloids: Defense against herbivores.
– Flavonoids: Pigmentation, UV protection.
– Chlorophylls: Photosynthesis.
(b) Utilities to man:
– Alkaloids: Drugs (e.g., morphine).
– Flavonoids: Antioxidants.
(c) Chemical tests:
– Alkaloids: Dragendorffβs reagent (orange precipitate).
– Flavonoids: Shinoda test (red color with Mg/HCl).
(d) Isolation procedure for caffeine (alkaloid):
1. Extract plant material with organic solvent.
2. Purify via column chromatography.
(e) Usefulness of caffeine:
Stimulant, improves focus.
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Question 5:
(a) Types of alkaloids:
1. True alkaloids (e.g., nicotine).
2. Protoalkaloids (e.g., ephedrine).
(b) Precursors:
– Nicotine: Ornithine + Nicotinic acid.
(c) Classification based on structure:
1. Pyrrolidine (e.g., hygrine).
2. Piperidine (e.g., coniine).
(d) Examples:
– Morphine (benzylisoquinoline).
– Quinine (quinoline).
(e) Importance:
– Morphine: Pain relief.
– Quinine: Antimalarial.
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