Estolones

Estolones are a class of lipid esters formed when the carboxyl group of one fatty acid forms an ester linkage with the hydroxyl group of a second fatty acid. When these linkages extend to form oligomeric chains, the products are generally referred to as estolides; estolones can be considered the basic, singly linked unit within that family. The result is a molecule that contains at least two fatty acyl units connected by an ester bond, with one unit contributing the carboxylate and the other contributing the hydroxyl-bearing moiety.

Estolones occur in natural lipids where hydroxylated fatty acids are present, and have been identified in seeds and seed oils of several plants as minor constituents relative to triglycerides. They influence physical properties of oils, such as viscosity and melting behavior, and may participate in lipid metabolism.

Formation can occur through enzymatic or chemical esterification. In nature, lipases or acyltransferases can link a hydroxyl-containing fatty acid to the carboxyl group of another fatty acid, forming an estolide linkage. In the laboratory, estolones can be prepared by selective esterification of hydroxy fatty acids with fatty acid derivatives, or by lipase-catalyzed condensation under controlled conditions.

Analytical characterization relies on separation and identification of the constituent fatty acid moieties, typically by GC-MS following hydrolysis and derivatization, along with NMR methods for linkage position and stereochemistry. Estolones are of interest in natural products chemistry and in the development of biobased lubricants and plasticizers due to their distinctive molecular architecture.