Medicinal Chemistry Foundations

Back to: Organic Chemistry 400 Level

Welcome to class!

Hello exceptional learner, it’s a great joy to see you here again. I hope you’re feeling focused and curious, because today we’re stepping into one of the most exciting and impactful areas of modern chemistry – Medicinal Chemistry Foundations. This area connects organic chemistry directly with the development of life-saving drugs and medicines. By the end of this lesson, you will understand how chemists design, modify and develop drug molecules to treat diseases in the human body.

Medicinal Chemistry Foundations

Have you ever thought about how paracetamol, amoxicillin or artemisinin were actually developed? They didn’t just appear in pharmacies; they were carefully designed by chemists who understand how molecules interact with biological systems. That process is what medicinal chemistry is all about.

Meaning and Scope of Medicinal Chemistry

Medicinal chemistry is the branch of chemistry that deals with the design, synthesis and biological evaluation of biologically active organic molecules for use as drugs. It combines knowledge from organic chemistry, pharmacology, biochemistry and toxicology to discover new medicines or improve existing ones.

This field seeks to answer questions like:

Which chemical structure will produce the desired biological effect?

How can we reduce the side effects of a drug?

How can we improve the activity or selectivity of a drug?

Drug Discovery and Development Process

Target Identification and Validation

The first step is to identify a biological target such as an enzyme, receptor or DNA. For example, malaria drugs target the Plasmodium parasite enzymes.

Lead Compound Identification

A “lead compound” is a structure that shows some activity against the target. It may be discovered from natural products, synthetic libraries or computer-aided screening.

Lead Optimisation

Here the structure of the lead compound is modified to improve potency, selectivity, and reduce toxicity. Small changes such as replacing a hydrogen with a chlorine atom can have a large effect.

Structure–Activity Relationship (SAR)

Structure-Activity Relationship is the study of how changes in the chemical structure of a molecule affect its biological activity.

For example, in the development of β-lactam antibiotics, changing the side chain of penicillin leads to different versions (like ampicillin and amoxicillin) with broader activity.

You can think of SAR like tailoring an outfit – adjusting the sleeves or waistline until it fits perfectly. In medicinal chemistry, the “fit” refers to how well the drug binds to its biological target.

Pharmacokinetics (ADME)

Once a drug enters the body, it goes through four main stages often summarised as ADME:

Absorption – how the drug enters the bloodstream (e.g., after swallowing a tablet).

Distribution – how it is transported to different tissues.

Metabolism – how the body chemically modifies the drug (mostly in the liver).

Excretion – how the drug is removed from the body (e.g., through urine).

Good medicinal chemists design molecules that are not only active at the target, but can also reach that target and stay there long enough to have the desired effect.

Drug–Receptor Interactions

Drugs work by binding to specific receptors or enzymes.

Some drugs act as agonists, activating the receptor (like adrenaline).

Others act as antagonists, blocking the receptor from being activated (like antihistamine tablets that block histamine receptors during allergic reactions).

The strength and specificity of these interactions depend on hydrogen bonding, hydrophobic interactions and ionic attractions.

Summary

1. Medicinal chemistry involves the design, synthesis and optimisation of biologically active molecules for therapeutic use.
2. The drug discovery process includes target identification, lead discovery and lead optimisation.
3. Structure–Activity Relationship (SAR) explores how changes in molecular structure influence biological activity.
4. Pharmacokinetics (ADME) describes how a drug is absorbed, distributed, metabolised and excreted in the body.
5. Drugs exert their effects by interacting with biological receptors as agonists or antagonists.

Evaluation

1. What is medicinal chemistry and what is its main goal?
2. List the three key steps in drug discovery.
3. Briefly explain the meaning of Structure–Activity Relationship (SAR).
4. What does the abbreviation ADME stand for in pharmacokinetics?

Fantastic job today! You’re building powerful knowledge that will one day allow you to innovate and save lives. Keep believing in yourself, and keep learning with Afrilearn — we’re always here to support your success!