Polyethers

Abstract

Several polyether antibiotics have found commercial application as anticoccidials in poultry farming and in improvement of feed efficiency for ruminants. These antibiotics are characterized by multiple tetrahydrofuran and tetrahydropyran rings connected by aliphatic bridges, direct C–C linkage, or spiro linkage. Other features include a free carboxyl function, many lower alkyl groups, and a variety of functional oxygen groups. These structural features enable transport of cations across lipid membranes. Some polyethers have found application as components in ion‐selective electrodes for use in clinical medicine or in laboratory studies involving transport studies or measurement of transmembrane electrical potential. The polyether class can be subdivided based on the number of carbon atoms in the backbone, ie, longest chain of contiguous carbons between the carboxyl group and the terminal carbon. The 30 C skeleton group accounts for about 60% of the polyethers for which structures have been determined. Monensin, widely used as an anticoccidial and feed efficiency enhancer, is an example of the 26 C backbone class. Maduramicin, another commercially important polyether, is shown as an example of the 30 C group with a sugar moeity. Many of the production procedures for polyethens utilize the separation of the mycelium followed by extraction using solvents such as methanol or acetone. A number of the polyethers can be readily crystallized. Polyethers such as monensin, lasalocid, salinomycin, and narasin are sold in many countries in crystalline or highly purified forms for incorporation into feeds or sustained‐release bolus devices. There are also mycelial or biomass products, especially in the United States, generally prepared by separation of the mycelium and then drying by azeotropic evaporation, fluid‐bed driers, or other types of commercial driers. The polyether antibiotics exhibit a broad range of biological, antibacterial, antifungal, antiviral, anticoccidial, antiparasitic, and insecticidal activities. They improve feed efficiency and growth performance in ruminant and monogastric animals. Only the anticoccidial activity in poultry and cattle, and the effect on feed efficiency in ruminants such as cattle and sheep are of commercial interest. It is estimated that the polyether ionophores constitute more than 80% of the total worldwide usage of anticoccidials. Bacteria belonging to the order Actinomycetales are the organisms reported to produce all of the polyethers. Most are secondary metabolites of Streptomyces sp. with the species hygroscopicus and albus accounting for about one‐third of the antibiotics. Monensin and salinomycin represent about 65–70% of worldwide usage of polyether antibiotics for controlling coccidiosis. Lasalocid, narasin, and maduramicin make up the remainder. Other compounds for coccidiosis control include nicarbazine, halofunginone, amprolium, and robenidine.

Crystalline structure of a new strontium-lasalocid complex: aqua bis-(lasalocid)-strontium(II) containing nine-coordinate Sr

“…At the origin of these processes, there is the property of forming lipophilic metal complexes, which can penetrate membranes and disrupt cation equilibria. 1,2 The molecular basis of this action are still debated; more specifically which of the oxygen atoms are directly involved in cation coordination. To date, this problem has been the object of many investigations almost invariably taking advantage of the concerted use of several experimental and computational techniques, which demonstrate both the relevance of the problem and its intrinsic difficulty.…”