ABSTRACT
Amino acids have become firmly established as building blocks for a wide variety of chemicals ranging from absorbents to pharmaceuticals. Nature, for the most part, uses 20 amino acids to build proteins. In addition to these proteinogenic amino acids, there is still diversity for specific applications and uses ranging from changes in the side chains of
α
-amino acids, a reversal of stereochemistry at the center, to positioning of the amino functionality at a site removed from the carboxylate group as in
β
- and
γ
-amino acids. These nonproteinogenic amino acids are commonly referred to as “unnatural,” even though some can be isolated from natural sources.
