Revision Chapter 2 BWK20803:

1. Explain the concept of phytochemistry and discuss its importance in the

study of natural products.

Phytochemistry is the study of the chemical compounds produced by plants,

particularly secondary metabolites such as alkaloids, flavonoids, terpenoids,
and tannins. These compounds often play ecological roles in plant defense,
pollinator attraction, and environmental adaptation. Phytochemistry is
essential in the study of natural products because it helps identify bioactive
compounds that can be developed into pharmaceuticals, supports the creation
of functional foods and natural health products, aids in the quality control of
herbal medicines, and contributes to sustainable agricultural practices. By
bridging plant biology and chemistry, phytochemistry plays a vital role in drug
discovery, nutrition, and ecological research.

2. Discuss the role of phytochemicals in plants and their significance in

human health. Provide examples of phytochemicals commonly used in
traditional medicine.

Phytochemicals play crucial roles in plants by protecting them against pests,

pathogens, and environmental stress, as well as aiding in reproduction through
pollinator attraction. In human health, these compounds are valued for their
therapeutic properties, including antioxidant, anti-inflammatory, antimicrobial,
and anticancer effects.

3. What are the major techniques used in the extraction and analysis of
phytochemicals from plant materials? Briefly describe each technique.
Solvent Extraction This involves soaking plant material in
solvents like ethanol, methanol, or water
to dissolve and extract phytochemicals.
It's a simple and widely used method for
obtaining crude extracts.
Soxhlet Extraction A continuous extraction process where
solvents are repeatedly evaporated and
condensed to extract compounds more
efficiently, especially useful for non-
volatile and thermally stable
phytochemicals.
Ultrasound-Assisted Extraction (UAE) Uses ultrasonic waves to break plant cell
walls, enhancing the release and yield of
phytochemicals while reducing extraction
time and solvent use
Chromatography Used for the separation, identification,
and quantification of phytochemicals.
High-Performance Liquid
Chromatography (HPLC) and Gas
Chromatography (GC) are common for
detailed analysis of complex mixtures
Spectroscopy These techniques help identify chemical
structures. For example, UV-Vis
spectroscopy detects compounds based
on light absorption, while Mass
Spectrometry (MS) and Nuclear
Magnetic Resonance (NMR) provide
detailed molecular information.
4. Classify phytochemicals based on their chemical structure and function.
Provide examples for each class.
phytochemical structure function example
Alkaloids Nitrogen- Defense against Morphine
containing herbivores and
compounds, pathogens;
often medicinal
heterocyclic. properties like
analgesic or
stimulant effects.
Flavanoids Polyphenolic Antioxidant, anti- green tea
compounds with inflammatory, UV
a C6-C3-C6 protection.
skeleton
Terpenoids Built from Aroma, Menthol
isoprene units pigmentation, and
(C5H8); include defense; many
mono-, sesqui-, have medicinal
di-, and properties.
triterpenes.
Phenolic Compounds with Antioxidant, curcumin
one or more antimicrobial, and
hydroxyl groups anti-inflammatory
attached to activities.
aromatic rings.
Terpenes Built from Aroma, Limonene
isoprene units pigmentation, and
only defense; many
have medicinal
properties
Sulfur containing Compound vitamins thiamin Biotin
compound containing and biotin, some
sulphur odorous
compounds and
several other
compounds,
which are
important from
the viewpoint of
human nutrition
and health.
5. Discuss the major differences between primary and secondary
metabolites in the context of phytochemistry.

• Primary Metabolites are essential for the basic survival and growth of plants.
They are directly involved in processes like respiration, photosynthesis, and
nutrient assimilation. Examples include carbohydrates, amino acids, nucleic
acids, and lipids. These compounds are universally present in all plant cells.
• Secondary Metabolites, on the other hand, are not directly involved in growth
or reproduction but play crucial roles in plant defense, attraction of pollinators,
and environmental adaptation. They are species-specific and structurally
diverse. Examples include alkaloids, flavonoids, terpenoids, saponins, and
tannins.

In summary, while primary metabolites are necessary for life-sustaining functions,

secondary metabolites enhance a plant’s survival in its environment and are the main
focus of phytochemistry due to their medicinal and ecological significance.

6. Differentiate between terpenes and terpenoids in terms of structure and

biosynthesis. Provide examples of each.
feature terpenes terpemoids
structure Hydrocarbons Modified terpenes with
oxygen groups
composition Carbon and hydrogen Carbon, hydrogen, and
only oxygen
biosynthesis From isoprene units Derived from terpenes
via further enzymatic
change
example Limonene Methol

7. Explain the medicinal significance of terpenoids and provide examples

of terpenoid-containing plants and their therapeutic uses.
Medicinal value due to their wide range of biological activities, including anti-
inflammatory, antimicrobial, antiviral, antimalarial, anticancer, and antioxidant
effects
Absinthe raditionally used as a digestive aid, anthelmintic (expels worms), and
to stimulate appetite.
Camphor Used topically as a counterirritant, analgesic, and antipruritic
(relieves itching). Found in vapor rubs and balms for cough, congestion, and
muscle pain Used topically as a counterirritant, analgesic, and antipruritic
(relieves itching). Found in vapor rubs and balms for cough, congestion, and
muscle pain
Menthol Provides a cooling sensation, used in cough drops, nasal sprays, and
topical pain relievers. Acts as a mild anesthetic and decongestant.
8. Describe the structural features of flavonoids and their classification.
How do they differ from other phenolic compounds?

Flavonoids are a class of polyphenolic compounds with a characteristic C6-

C3-C6 carbon structure, consisting of two benzene rings connected by a
three-carbon chain. They are classified into several subtypes based on
structural differences, including flavones, flavonols, isoflavones, anthocyanins,
flavanols, and flavanones, each varying in functional groups like hydroxyl and
sugar attachments. Unlike other phenolic compounds, such as phenolic acids
(which have a single aromatic ring and a carboxyl group), flavonoids have a
more complex structure and are often more diverse in their biological
activities, including antioxidant, anti-inflammatory, and anticancer properties.
This structural complexity and functional diversity distinguish flavonoids from
simpler phenolic acids and other polyphenols, which may follow different
biosynthetic pathways.

9. What are alkaloids, and how are they classified based on their chemical
structure? Provide examples of each class.

Alkaloids are a diverse group of naturally occurring nitrogen-containing

compounds primarily found in plants, fungi, and some animals. They are
known for their biological activity and often have pharmacological effects on
humans and other animals
1. Pyridine and Piperidine Alkaloids
o Structure: Contain a pyridine ring (C₆H₅N) or piperidine ring (C₆H₁₁N).
o Examples:
▪ Nicotine A stimulant found in tobacco.
▪ Coniine A toxic compound found in poison hemlock.
2. Quinoline and Isoquinoline Alkaloids
o Structure: Derived from quinoline or isoquinoline rings (C₉H₇N).
o Examples:
▪ Quinine – Used in the treatment of malaria.
▪ Morphine analgesic derived from opium.
3. Indole Alkaloids
o Structure: Contain an indole ring (C₈H₉N).
o Examples:
▪ Reserpine – Used as an antihypertensive.
▪ Vincristine – Used in cancer treatment.
4. Terpenoid Alkaloids
o Structure: Contain a terpenoid backbone in addition to the nitrogen-
containing heterocyclic ring.
o Examples:
▪ Atropine – Used as an anticholinergic drug.
▪ Sparteine – A muscle relaxant.
5. Steroid Alkaloids
o Structure: Alkaloids with a steroid backbone and nitrogen.
o Examples:
▪ Solanine – Found in potatoes, it can be toxic in high doses.
▪ Tomatine – Found in tomatoes.
6. Tropane Alkaloids
o Structure: Contain a tropane ring (C₇H₁₁N).
o Examples:
▪ Hyoscyamine – Used in medicine as an antispasmodic.
▪ Cocaine – A stimulant and local anesthetic.
10. Describe the characteristics of sulphur-containing phytochemicals and
their significance in human health.
Sulfur-containing phytochemicals, found in plants like garlic, onions, and
cruciferous vegetables (e.g., broccoli and cabbage), possess bioactive
compounds such as allicin and sulforaphane that offer numerous health
benefits. These compounds are known for their anticancer properties,
antioxidant effects, and ability to reduce inflammation and lower cholesterol.
Sulfur compounds help detoxify the body, enhance cardiovascular health, and
combat microbial infections. They are particularly significant in preventing
chronic diseases like heart disease and cancer, highlighting their importance
in a healthy diet.

11. What are steroids, and how do they differ from other terpenoids?
Explain their biosynthetic origin.
Steroids are a class of lipids characterized by a core structure of four fused
carbon rings, and they play vital roles as hormones (e.g., cortisol, estrogen)
and components of cell membranes (e.g., cholesterol). They differ from other
terpenoids, which are derived from isoprene units and typically have flexible,
linear, or cyclic structures. While steroids have a rigid, tetracyclic ring system,
terpenoids can range in complexity and often serve ecological functions like
attracting pollinators or defending against herbivores. Steroids are
biosynthesized from squalene, a triterpene, via the mevalonate pathway,
undergoing cyclization to form lanosterol and then further modifications to
produce steroid hormones. In contrast, terpenoids follow different biosynthetic
pathways depending on their size and function, starting from simpler isoprene
precursors.