Drugs as Organic Molecules

Question 1

How can organic molecules be classified?

Answer 1

Aromatic
* Form a 6 carbon ring with alternating single and double bonds
* Carbons are numbered from the atom in which the principle
functional group is attached.

Aliphatic
* Carbon chain (root) with functional groups attached to it.
* The carbon is numbered starting from the carbon starting at the functional group which defines the molecule type.
* The parent molecule is determined by the number of carbons in the longest root

Question 2

What are the alkanes?

Answer 2

Aliphatic organic molecules containing only Carbon and hydrogen. Aka have no functional groups or double bonds.

Methane, Ethane, Propane, Butane, Pentane etc…

Question 3

Describe the following molecular group: alkene?

Answer 3

Contains a C=C bond

Question 4

Describe the following molecular group: amine?

Answer 4

Contains an NH2 group

Question 5

Describe the following molecular group: alcohols (suffix = ol)?

Answer 5

-OH group

Question 6

Describe the following molecular group: Halides?

Answer 6

Contains a Halogen functional group e.g. Chloride, Bromide, Iodide, Fluoride etc

Question 7

Describe the following molecular group: carboxylic acid?

Answer 7

Contains a COOH group

Question 8

Describe the following molecular group: ketone?

Answer 8

Contains a C=O group

Question 9

Describe the following molecular group: amides?

Answer 9

Contains a R-C (=O) - NH2 group

Question 10

Describe the following molecular group: Ether?

Answer 10

Contains a C-O-C group

Question 11

Describe the following molecular group: Ester?

Answer 11

Contains a R-C (=O)-O-R’ group

Question 12

Describe the following molecular group: phenols?

Answer 12

Contains an OH group attached to a benzene ring

Question 13

What is valency?

Answer 13

This is the number of bonds an atom has in its uncharged state.

I.e. Take Methane CH4, the carbon has a valency of 4 as it has 4 bonds. Each Hydrogen atom has a valency of 1

Question 14

Name the following molecule and explain how molecules are named?

F-CH2CH2CH2-OH

Answer 14

3-fluoropropanol

The number of carbons in the longest chain provides the stem of the name (prop). (The first carbon is defined by the functional group)

The side chain is named according to the carbon number it is attached to (3-fluoro).

A prefix is added with >1 identical side chain (di, tri etc). The suffix is determined by the main functional group (ol).

Question 15

Describe how changes in functional groups of barbituric acid can affect its pharmacological activity?

Answer 15

By adding a phenyl group to the carbon 5 on the benzene ring it will have anticonvulsant properties, if you increase the number of Carbons to the alkyl group* will become hypnotic.

A phenyl group is when you remove a H from a carbon a benzene ring.

Once there are more than 5 carbons in the alkyl group it will become a covulsant.

Question 16

What type of molecules are the volatile anaesthetics?

Answer 16

They are halogenated hydrocarbons or ethers (Ethers are more stable).

Question 17

How do the different halogens influence the pharmacological activity of the volatiles anaesthetics?

Answer 17

The addition of chloride or bromide increase potency

The addition of fluoride increases stability

Question 18

Describe the basic components of local anaesthetics and how they can be categorised?

Answer 18

Local anaesthetics have 3 different components:
* Aromatic group
* Intermediate chain
* Amine group

They are split into esters (i.e. procaine, tetracaine) and amides
dependent on the intermediate chain. (these influence the speed of metabolism)

Question 19

What happens to Midazolam in acidic conditions?

Answer 19

Midazolam contains an amine group which acts as a weak base forming an ammonium ion. In acidic conditions it becomes ionised (making it water soluble) and the benzene ring ‘opens’.

At physiological pH, the amine group is incorporated into a
benzodiazepine ring and the ring becomes closed making it
**non-ionised, lipid soluble and can cross the BBB. This is a pH dependent ring closure. **

Question 20

Describe the tautomerisation of thiopentol?

Answer 20

Thiopental is a weak acid and can exist in 2
different structural forms dependent on pH.

It is prepared in an alkaline environment to make it
ionised (pKa 7.6) and water soluble. This occurs by
substituting a proton for a sodium making it an enol.

At physiological pH, it undergoes tautomerization
(transforms) to a lipid soluble molecule by dissociating
the sodium to bind to the proton and therefore once
again form the unionised molecule as a ketone.