Amino acids represent one of the key building blocks of Nature as the form the basis of all proteins. Natural alpha-amino acids all feature a common structural element that is the alpha-amino acetic acid moiety (=glycine). 

Substituents on the alpha-position define the nature and reactivity of amino acids, and we can distinguish between e.g. aliphatic amino acids (alanine, valine, leucine, isoleucine), aromatic amino acids (phenylalanine, tyrosine, histidine), sulfur-containing amino acids (methionine, cysteine) etc.

The sterical demand, polarity, charge, and possible dipol interactions define not only the shape of a proteinogenic biomolecule, but are also key parameters to be considered in the interaction of a biomolecular target and its designated drug molecule.