What is Medicinal Chemistry (section 7)

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Section 7: Role of Natural Products in Drug Discovery

Natural products are chemical compounds that come from living organisms — plants, animals, microbes, and marine organisms. For centuries, humans have used natural substances to treat diseases. Even today, natural products play a major role in drug discovery and development.

In this section, you will learn how natural substances have been used in the past, how they are still important in modern drug discovery, and the advantages and challenges of using them.

1. What are Natural Products?

Natural products are organic molecules made by living organisms. They are found in:

  • Plants – alkaloids, flavonoids, terpenoids
  • Microorganisms – antibiotics like penicillin, streptomycin
  • Marine organisms – anticancer agents from sea sponges
  • Animals – toxins, hormones

Natural products can be used directly as medicines, or they can serve as templates (starting points) for designing new drugs.

2. Historical Importance of Natural Products

For thousands of years, natural products were the only source of medicines.

Examples from history:

  • Willow bark: Used for fever and pain, contains salicin (basis for aspirin).
  • Cinchona bark: Used by South American tribes to treat malaria (contains quinine).
  • Opium poppy: Source of morphine, used for pain relief.
  • Foxglove plant: Source of digoxin, used to treat heart failure.

Traditional medicine systems like Ayurveda, Traditional Chinese Medicine (TCM), and Unani rely on natural products.

3. Contributions to Modern Medicine

Many modern drugs are natural products or derived from them.

Natural Product

Source

Use

Penicillin

Fungus (Penicillium)

Antibiotic

Quinine

Cinchona bark

Anti-malarial

Morphine

Opium poppy

Painkiller

Paclitaxel

Pacific yew tree

Anticancer

Artemisinin

Artemisia annua

Anti-malarial

Lovastatin

Fungus (Aspergillus)

Lowers cholesterol

Streptomycin

Streptomyces bacteria

Antibiotic

Natural products have given us:

  • Over 60% of current anticancer drugs
  • Over 75% of antibiotics
  • Several heart, liver, and pain medicines

4. Why Are Natural Products So Useful?

Natural products are valuable because:

  • They have unique and complex structures not easily made in a lab.
  • They are often biologically active, meaning they affect cells or enzymes.
  • They show diversity, offering many types of molecules.
  • They may act on multiple targets, which is useful in diseases like cancer.

Nature has evolved these molecules over millions of years for survival — they are biologically “tuned”.

5. Methods of Using Natural Products in Drug Discovery

A. Direct Use (Unmodified)

Some natural products can be used directly as drugs.

Example: Penicillin, Morphine

B. Semi-Synthetic Derivatives

Scientists change the structure slightly to improve activity, reduce side effects, or increase stability.

Example: Ampicillin (from penicillin)

C. Natural Product as a Lead

Used as a template to design synthetic drugs.

Example: Salicylic acid → Aspirin

6. Sources of Natural Products

i. Plants

  • Largest source of natural medicines
  • Contain alkaloids, flavonoids, glycosides, tannins, etc.
  • Examples: Neem, Tulsi, Aloe vera

ii. Microorganisms

  • Major source of antibiotics
  • Especially Streptomyces, Penicillium, and Cephalosporium species

iii. Marine Organisms

  • Sea sponges, algae, and corals produce compounds with anticancer, antiviral activity.
  • Example: Cytarabine from sea sponge

iv. Animal Toxins

  • Snake venom, frog skin, etc., are being studied for pain and clotting disorders.

7. Techniques to Study Natural Products

A. Extraction

  • Solvents like ethanol, methanol, or water are used to extract compounds.

B. Isolation

  • Techniques like chromatography (TLC, column, HPLC) are used.

 

C. Structure Elucidation

  • Spectroscopy: NMR, MS, IR to determine chemical structure.

D. Bioassay-Guided Fractionation

  • Extract is tested for activity → active portion is isolated → purified → tested again.

8. Challenges in Using Natural Products

Despite their usefulness, natural products also pose some challenges:

Challenge

Explanation

Difficult to isolate

Complex mixtures with many components

Reproducibility issues

Plant quality depends on season, location, etc.

Low yield

Some compounds are present in small amounts

Complex structures

Hard to synthesise or modify in lab

Time-consuming process

Requires extensive purification and testing

Sustainability concerns

Overharvesting rare plants or animals is harmful

9. Modern Technologies in Natural Product Research

To overcome challenges, scientists now use:

  • Metabolomics: Study of all small molecules in an organism
  • Dereplication: Quickly identifying known compounds to avoid duplication
  • High-Resolution MS and NMR: Better tools for structure determination
  • Genomic mining: Predicting natural products from DNA sequences
  • Synthetic biology: Using engineered microbes to produce plant compounds

10. Natural Products in Modern Research Areas

  • Cancer: Taxol, Vincristine, Camptothecin
  • Antibiotic Resistance: New antibiotics from soil bacteria and fungi
  • COVID-19 Research: Phytochemicals screened for antiviral properties
  • Neurodegenerative Diseases: Curcumin, resveratrol for Alzheimer’s

 

11. Role of Natural Products in Ayurveda and Modern Integration

In India, the rich heritage of Ayurveda provides many natural formulations. Scientists now:

  • Analyse these formulations using modern chemistry
  • Standardise them for consistent quality
  • Validate them through clinical research

This integrative approach bridges traditional knowledge with evidence-based medicine.

12. Summary Table – Key Natural Drugs

Drug

Source

Use

Penicillin

Fungus

Antibiotic

Morphine

Opium poppy

Pain relief

Quinine

Cinchona bark

Anti-malarial

Taxol

Pacific yew tree

Anticancer

Artemisinin

Artemisia annua

Anti-malarial

Lovastatin

Fungus

Cholesterol

Digoxin

Foxglove plant

Heart failure

Reserpine

Rauwolfia serpentina

Antihypertensive

Conclusion

Natural products have been and continue to be a powerful source of life-saving drugs. From ancient healing herbs to modern antibiotics and anticancer agents, nature provides both inspiration and raw material for drug discovery. As science advances, combining natural wisdom with modern technology will continue to uncover new treatments for the world's toughest diseases.

 

 

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