Medicinal chemists have been using fluorine as a Hydrogen substitute in drug discovery for a long time. It has been used in drug discovery to the extent that nearly 25% of the drugs today including some of the block busters have fluorine in them; like Prozac, Lipitor and Pervacid.
Why do chemists use it?
As the review in J. Med Chemistry highlights, fluorine has multiple effects.
Being more electrophilic than hydrogen with a lipophilic atom, it tends to make the compound slightly more lipophilic which increases its membrane penetration. The C-F bond may also change the confirmation and help in the binding of the drug to its target. In addition, since F may not be targeted as much by the P450 enzymes in the liver, it might make the drug more stable and less prone to degradation that increases its half life.
If there are so many advantages to this molecule, no wonder companies like Fluorinov Pharma which was acquired by Trillium have been focusing on the Fluorine discovery platform.