D9 – Drug Design (HL)

D9 – Drug Design (HL)

D.9.1 Discuss the use of a compound library in drug design

Over the years, molecules of various substances have been isolated or synthesized, and tested for their pharmacological properties.

These form a “compound library”, as compounds from these libraries can be utilized to make changes to the structure to produce similar drugs.

It used to be that this was a time consuming process, until…..

D.9.2 Explain the use of combinatorial and parallel chemistry to synthesize new drugs.

Combi-Chem!!! Ahhh, combinatorial chemistry…much better. Thousands of possible compounds are tested to

research the biological activity of each. Computer-controlled syringes carry out

repetitive chemical techniques. Parallel synthesis can produce smaller, focused

libraries by using robotics to carry out identical chemical processes such as adding fixed volumes of substances.


An example of parallel synthesis is eight different carboxylic acids can be reacted with eight different alcohols.

Question: What functional group is created, and how many different compounds can be formed?

A: Esters are formed and 64 (8x8) different combinations can be formed.


Solid-phase synthesis uses very small resin beads (100 µm in diameter) to covalently bonded starting materials.

For example, compound X, Y and Z are all covalently bonded onto resin beads. They are then mixed together to react. How many different combinations do you have (counting the resin bead)?

A: 3x3=9


Now you have nine different combinations (● X-X ●X-Y, ●Y-X, etc.). You split the compounds

up, and react them again with X, Y, and Z. How many combinations do you now have?

A: 27What if you reacted a third time?B: 81 These combinations are tested to see how they affect

enzymes and bind to receptor cells. This information is used to build combinatorial libraries.

D.9.3 Describe how computers are used in drug design.

Molecular modelling software allows scientist to build 3-D representations of molecules and mimic their molecular behavior.

D.9.4 Discuss how the polarity of a molecule can be modified to increase its aqueous solubility and how this

facilitates distribution around the body. Take a look at salicylic acid and it’s polarity (and

ability to donate hydrogen ions), and compare it to acetylsalicylic acid in your data booklet:

Because of it’s acidity, it would damage the esophagus and stomach, so it needed to be chemically modified.

Initially it was reacted with sodium hydroxide to create sodium salicylate—a soluble salt of salicylic acid


facilitates distribution around the body.

However, this was bitter tasting and still irritating to the stomach lining. So aspirin was developed by creating an ester to make it less acidic, and therefore less irritating. It is also tasteless.

However, this form is also insoluble in water. So the salt of acetylsalicylic acid can also be purchased.

The more insoluble a substance is, the longer it takes to dissolve. The longer it takes, the less effective it is.


facilitates distribution around the body.

Basic molecules can also be turned into a salt by adding hydrochloric acid.

For example, Prozac® can be made into fluoxetine hydrochloride. This makes it water soluble.

D.9.5 Describe the use of chiral auxillaries to form the desired enantiomer.

As you know, different enantiomers can have different biological effects.

A chiral auxillary attaches to a non-chiral compound to be synthesized, so only the desired enantiomer is created.

Due to steric hindrance, the auxillary directs the “attacking molecule” to attack from only one side.

The auxillary can be removed and then re-used. This process is used when synthesizing Taxol.

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D9 – Drug Design (HL)