D.9.4+Drug+Design


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

The most efficient way for medicine to be carried throughout the body is through the aqueous plasma of our blood. Unfortunately, many drugs are non-polar due to their long hydrocarbon chains. However, the non-polar medicine can be modified to become more polar. One method is to produce the medicine in the form of ionic salts. The acidic and basic groups of the structure can gain or lose hydrogen ions to form these salts.

If the medicine contains an amine group, then it can be converted into its hydrochloride salt, much like in the following reaction:

NH3 + HCl → NH4+Cl¯ examples:
 * selective serotonin re-uptake inhibitor (SSRI) fluoxetine, aka Prozac® (for depression)
 * opiates, such as diamorphine (heroine)

In this form, Prozac® has... C17H18F3NO + HCl → C17H19F3N+O + Cl¯
 * 1 carbon trifluoride group (yellow)
 * 1 ether group (red)
 * 1 amino group (blue)

In its hydrochloride salt form, an extra hydrogen atom bonds to the nitrogen, which has been oxidized and is now a positive ion. The entire molecule is now a salt and can be more easily dissolved into the blood stream.

Fluoxetine (Prozac®) C17H18F3NO

Below is Prozac® in its hydrochloride form. (Note: The image above has been scanned and uploaded from the //IB Chemistry Study Guide// by Geoffrey Neuss)

If the medicine contains a carboxylic acid, then it can be converted into its anion and administered as its sodium or calcium salt.

RCOOH + NaOH → RCOO- + Na + H2O

When they are in a salt form, they can be dissolved into their ion forms, unlike the original insoluble form.

examples:
 * soluble aspirin (shown below in its sodium salt form)