medicinal chemistry

1. Medicinal Chemistry
Chapter 1 Introduction
College of Pharmacy, SDU

2. Definition
• Medicinal chemistry is a chemistry-based
discipline, involving aspects of biological, medical
and pharmaceutical sciences. It is concerned with
the invention, discovery, design, identification and
preparation of biologically active compounds, the
study of their metabolism, the interpretation of
their mode of action at the molecular level and
the construction of structure-activity
relationships (SARs).

3. • In particular, Medicinal chemistry also
involves the discovery of new chemical
entities for the treatment of diseases and the
systematic study of the structure-activity
relationships of the active compounds. Such
studies provide the basis for development of
better medicinal agents from lead compounds
found via random screening, systematic
screening and rational design.

4. • Drug is any substance presented for treating,
curing or preventing disease in human beings
or in animals. It may also be used for making a
medical diagnosis or for restoring, correcting,
or modifying physiological functions.

5. • Structure-activity relationship (SAR) is the
relationship between chemical structure and
pharmacological activity for a series of
compounds.
• Lead compound is a compound that has a
desirable biological activity with therapeutic
relevance, but typically has some shortcoming
that is likely to be overcome through the
development of analogs.

6. Emphasis
• 1. Chemcially structural feature, physico-chemical
property, stability.
• 2.Biological effect, adverse effects,
biotransformation etc.
• 3. Structure-activity relationship, drug targets in
living bodies as well as mode of action.

7. The important role of
drugs in human society
• Drugs have irrevocably changed the fabric of
society by improving both the individual
quality of life and life expectancy.
• Some examples are shown as follows:

8. • 1. Bacterial and virus infections: polio,
smallpox, tuberculosis and related diseases
have, to a very major extent, become minor
public health concerns.
• 2. An increase in life expectancy resulting
from drug therapy has also led to a shift in
population demographics toward a more
healthy, elderly population.
• 3. Drug regimens for birth control have
improved individual life choices and the
quality of life.

9. • 4. HIV protease and reverse transcriptase
inhibitors for the treatment of HIV infections have
changed a disease with a fatal prognosis to a
potentially chronic one.
• 5. Cancer is also being viewed as a potentially
chronic, rather than fatal disease with newer, non-
cytotoxic approaches.
• Notes: HIV, Human immunodeficiency virus

10. Section 1
Origins of Medicinal Chemistry
1. Early investigations of natural products
• 1.1.In the so-called pre-scientific era
• Natural products having a history as folk
remedies were in use. Fore examples, opium,
belladonna, cinchona bark, etc. Many drugs
originally used as folk remedies, nowadays,
have been abandoned.

11. • 1.2. In the late eighteenth and early nineteenth
centuries, chemical experimentation led
ultimately to its use in the discovery of new
drugs.
• In 1853, Henry How conceived the idea that
functional groups in natural products might be
modified by chemical reagents.
He heated morphine with methyl iodide, hoping to
convert the alkaloid to codeine. He obtained, however, a
new substance of the quaternary salt of morphine.
HO O
H OH
N

12. • In 1898, the first commercially available
semisynthetic morphine derivative (ethyl ether)
was introduced as a cough sedative in preference
to codeine or other opiates.
• Meanwhile, diacetylmorphine was introduced as a
safer pain reliever than morphine. It quickly
became popular throughout the world.
• Four years passed before its addictive properties of heroin
were recognized. Laws were later passed by governments
to restrict its use.

13. • 1.3. Developments of MC Leading to Various
Medicinal Classes of Drugs
• During the 1840s, the first use of synthetic
organic chemicals were introduced for
anesthesia during a tooth removal, such as
nitrous oxide, ether, and chloroform.
• In 1864, barbituric acid had been synthesized as
a useful hypnotic.

14. • In 1875, salicylic acid was introduced as a
possible cure for typhoid fever. It was found to
be an effective antipyretic.
• In 1899, Aspirin was marketed as an antipyretic
without the unpleasant side effects. This
indicated that the chemical structures from
natural products were changed into better drugs.
• Medicinal Chemistry began.

15. 2. Fast Development from 1900’s to 1960’s
• 1920’s~1930’s: Anesthetics, Hypnotics, Analgesics
were used extensively. In research for functional
“pharmacophore”, structure-function relationship
was investigated gradually.

16. • After 1930’s: The development of new drugs was
speeded greatly by the close combination of
Medicinal Chemistry and Experimental
Pharmacology.
• Theory of antimetabolite was formed by using
metabolic products as lead compounds.
• Discovery of penicillin which is the first antibiotics
is an epoch-making achievement.
• Afterward, tetracycline, streptomycin, chloramphenicol,
erythromycin were introduced one after another.

17. • In 1940’s, the first drug used for treating cancer
as a biological alkylating agent was nitrogen
mustard, which began tumor chemical therapy.
• In 1960’s, oral steroidal contraceptive agents
were discovered. Corticosteroids have become
an important drugs.

18. • After 1950’s, aging disease, cerebrovascular and
cardiovascular diseases became first reason for
human death. New drugs design based on
enzymes or receptors as drug targets.
• In 1964, first β-Adrenergic blocking agent,
Propranolol, was marketed.
• In 1979, Nifedipine, Calcium Channel Blocker was
marketed.
• In 1981, Captopril, Angiotensin Converting Enzyme
(ACE) Inhibitor was launched.

19. Future of Medicinal Chemistry
• New drugs will be
discovered or invented by
investigating human
genomics and human
disease genomics.

20. 3. Drug Target and Drug Design
• Mechanism based drug design
• Structure based drug design
• Known targets: 480，receptors: 45%; enzymes: 28%
(See p5~6)

21. 3.1. Receptor Used as Drug Target
• Receptors: M acetylcholine receptor; adrenergic
receptor; angiotensin receptor; dopamine receptor;
serotonin receptor; opioid receptor etc.
• Drugs effecting on receptors：
• Agonist；Antagonist
Drug
Receptor

22. • Agonist is an endogenous substance or a drug
that can interact with a receptor and initiate a
physiological or a pharmacological response
(contraction, relaxation, secretion, enzyme
activation, etc.).
• Antagonist is a drug or a compound that
opposes the receptor-associated responses
normally induced by another bioactive agent.
• Partial agonist is an agonist which is unable to
induce maximal activation of a receptor
population, regardless of the amount of drug
applied.

23. 3.2. Enzyme Used as Drug Target
• Enzyme: Angiotensin Converting Enzyme
(ACE), Cycloxygenase （ COX2 ） ， β-
Lactamase, Acetylcholine Esterase etc.
• Drugs effecting on enzyme: Enzyme Inhibitor

24. 3.3. Ion Channal Used as Drug Target
• Ion Channal: Calcium Ion Channal, Potassium
Ion Channal, Sodium Ion Channal, Chloride Ion
Channal, etc.
• Drugs effecting on Ion Channal: Calcium Channal
Blocker, Potassium Channal Blocker, Sodium
Channal Blocker, etc.

25. 3.4. Nucleic Acid Used as Drug Target
• Nucleic Acid: RNA, DNA
• Drugs: antiviral agent,
quinolone agent, etc.

26. • Antisense technology
• Antisense drugs are short stretches of DAN
analogs which bind to specific complementary
areas of the mRNA. In doing so, they can induce
a nuclease which cleaves the mRNA at the site
of the binding or can physically block translation
or other steps in mRNA processing and
transport, thus stopping protein synthesis.

27. Flowchart for
evaluation
of new chemical
entities

28. R & D Model of Modern Drugs

29. Section 2
Nomenclature of Drug Substances
• INN: International Non-proprietary Names for
Pharmaceutical Substance, that is, common
names by national or international
nomenclature commissions
• Chemical Name by international union for
pure and applied chemistry (IUPAC) and
international union of biochemistry (IUB)

30. • CADN: Chinese Approved Drug Names
• English Chemical Name based on
nomenclature of chemical abstracts (CA)
• Trade Name

31. Questions
• 1. To master the following definitions: medicinal
chemistry, drug, structure-activity relationship,
lead compound, Antisense drugs.
• 2. to be familiar with main research contents of
medicinal chemistry.
• 3. To understand orgins of medicinal chemistry.