Incorporation of fluorine into a molecule can have a profound effect on the biological activity and metabolism of a molecule relative to it's hydrocarbon analogue. Interest in the medicinal and biochemical applications for fluorocarbons began in the 1950's with the discovery that (1) fluoroacetic acid mimics acetic acid but stops the Krebs cycle, and (2) fluorosteroids, in some cases, surpass the biological activity of naturally occurring hormones.
There are currently many uses for fluorinated compounds. Among them are antivirals, anitbacterials, herbicides, and insecticides. Recently synthesized fluorinated molecules are used to treat HIV, malaria, obesity, mental illness, cancer, alzheimers, etc..
There are several reasons for the altered biological activity of fluorinated molecules. Fluorine has about the same atomic radius as hydrogen. Because of this, fluorine does not alter the geometric configuration of the molecule and can mimic hydrogen at, for example, enzyme receptor sites. Fluorine's small size and high electronegativity sets it apart from the other halogens. Once in place on a molecule it is not as easily replaced. Since fluorine is very electronegative, it alters the electronic configuration of the molecule. Addition of fluorine increases the lipophilicity of the molecule allowing it to pass through membranes easier, which increases the distribution of the molecule throughout biological systems. Also, the carbon-fluorine bond is stronger than the carbon-hydrogen bond, which results in an increased oxidative and thermal stability of the molecule.
Early research with the fluorination of organics often involved dangerous and/or expensive reagents that often delivered multiple fluorines to the target molecule. New reagents have appeared that are safe, stable, inexpensive, and deliver a single fluorine to the molecule. These "tamed" reagents are the focus of intense research and have promoted current interest in the fluorination of molecules.
