'''dipeptide''' is a sometimes ambiguous designation of two classes of organic compounds: Its molecules contain either two amino acids+ joined by a single peptide bond+ or one amino acid with two peptide bonds.
In this usage, ''X dipeptide'' (with ''X'' designating an amino acid) must be understood as ''di-X peptide''. This nomenclature is continued by tripeptide+ (three amino acids, two peptide bonds), tetrapeptide+, and so on; longer chains are called oligopeptide+, polypeptide+, protein+.
Dipeptides are produced from polypeptide+s by the action of the hydrolase+enzyme+dipeptidyl peptidase+. Dietary proteins are digested to dipeptides and amino acids, and the dipeptides are absorbed more rapidly than the amino acids, because their uptake involves a separate mechanism. Dipeptides activate G-cells+ found in the stomach to secrete gastrin+.
The Bergmann azlactone peptide synthesis is a classic organic synthesis+ for the preparation of dipeptides.
In this usage, ''X dipeptide'' is taken literally: One amino acid ''X'' is equipped with two minimal peptide bonds: The C terminus COOH becomes COCH3, the N terminus NH2 becomes NHCH3.
For instance, alanine dipeptide+ is CH3CONHCH(CH3)CONHCH3.