Nonactin is a member of a family of naturally occurring cyclic ionophores known as the macrotetrolide antibiotics. The other members of this homologous family are monactin, dinactin, trinactin and tetranactin which are all neutral ionophoric substances and higher homologs of nonactin. Collectively, this class is known as the nactins. Nonactin is soluble in

methanol Methanol (also called methyl alcohol and wood spirit, amongst other names) is an organic chemical and the simplest aliphatic alcohol, with the formula C H3 O H (a methyl group linked to a hydroxyl group, often abbreviated as MeOH). It is a ...

dichloromethane Dichloromethane (DCM or methylene chloride, methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odour is widely used as a solvent. Although it is not miscible with ...

, ethyl acetate and DMSO, but insoluble in water.

Sources

Nonactin is commercially available; as of 2006, these bacterial species produce nonactin: '' Streptomyces tsukubensis'', '' Streptomyces griseus'', '' Streptomyces chrysomallus'' and '' Streptomyces werraensis''.

Total syntheses Total synthesis is the complete chemical synthesis of a complex molecule, often a natural product, from simple, commercially-available precursors. It usually refers to a process not involving the aid of biological processes, which distinguishes ...

have been reported.

Structure and properties

Nonactin was isolated by Corbaz ''et al.'' in 1955 from bacterial strains. It is composed of four tetrahydrofuran rings and four esters linked by saturated aliphatic chain sections. Nonactin has a 48-member ring, built from 40 carbon and 12 (8 on the ring, 4 as

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bo ...

s) oxygen atoms. Despite the 16 stereogenic centers, Nonactin is a meso compound, and therefore achiral. Liquid chromatography-mass spectrometry offers a modern approach to obtain more detailed process control data than the spectrophotometric and chromatographic measurements used in the past.

Reactions

Nonactin is known for its ability to form complexes with

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a ...

cations, most notably potassium and sodium. In general, nonactin (and other members of the nactin family) exhibits binding preferences for some ions over others. This ion selectivity is seen in other macrocyclic ligands, such as the cyclic ionophore valinomycin, which is also an antibiotic, and crown ethers. Although nonactin (and all nactins) exhibits an especially high cation selectivity for potassium ions over sodium ions or rubidium ions, it exhibits the highest selectivity for ammonium ions and thallium ions. Due to this property, nonactin is also called "ammonium ionophore". During complexation, the nonactin backbone convolutes into a pattern resembling the seam of a tennis ball. In the potassium-nonactin complex, the potassium ion is entirely surrounded by four carbonyl oxygen atoms and the four oxygen atoms of the tetrahydrofuran ring. These eight oxygen atoms surrounding the ion are nearly equidistant from it and adopt a nearly cubic coordination sphere around the ion. In this complex, all polar carbonyl groups point inwards and nonpolar moieties point outwards, thus building up a hydrophobic exterior for the complex and making it soluble in lipid membranes. This is how nonactin is able to transport potassium ions across lipid membranes.

Biological effects

Nonactin has been reported to specifically inhibit the processing of cytoplasmic precursor proteins destined for the

mitochondria A mitochondrion (; ) is an organelle found in the Cell (biology), cells of most Eukaryotes, such as animals, plants and Fungus, fungi. Mitochondria have a double lipid bilayer, membrane structure and use aerobic respiration to generate adenosi ...

. It is able to uncouple the oxidative

phosphorylation In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...

of mitochondria of rat liver in a low concentration, and can also carry cations across biological and artificial membranes. A nactins mixture, purposely enriched in tetranactin and poor in nonactin, known as polynactin(C), was used as a pesticide, but since 2004 is not used any more, presumably because its residuals appeared in food.Notification
the World Trade Organization's revocation of Polynactin agricultural usage, July 20, 2004.

Applications

Nactins have no known medical use. Ultrapure nonactin, practically free of other nactins, is used for ammonium-specific electrodes.

Sources

Structure and properties

Reactions

Biological effects

Applications

References

Further reading