Amino acids are molecules which contain both amino and carboxyl groups. In a generic sense the term refers to α-amino acids which are the constituents of proteins. The stereochemistry of amino acids is de?ned by D and L enantiomers. The 20 proteinogenic amino acids are L-isomers, and their enantiomeric D-isomers are rarely found in nature. The estimated 100,000 or more di?erent proteins in life consist from the twenty di?erent L-α-amino acids connected by peptide bonds between the carbonyl and amino groups of amino acid residues. Although the so-called 20 proteinogenic amino acids are found in all forms of life, D-amino acids and peptides containing them have been discovered to play an important part in a range of biochemical systems.
Amino acids and their N-protected derivatives, e.g. Boc and Fmoc amino acids, have vital roles in technology since they are utilized to synthesize various bioactive substances from other molecules, for example peptide sweeteners, nutritional supplements, cosmetic materials, surfactants, and synthetic precursors of pharmaceuticals like insulin. Typical amino acids, their protected and biologically-modi?ed reagents, non-proteinogenic amino acids, and oligopeptides are shown as follows.