CHAPTER SIXTEEN Ethers, Epoxides, and Sulfides POLYETHER ANTIBIOTICS ne way in which pharmaceutical companies with metal ions the structure of the monensin- search for new drugs is by growing colonies of sodium bromide complex is depicted in Figure 16.3b microorganisms in nutrient broths and assay. where it can be seen that four ether oxygens and ing the substances produced for their biological ac- two hydroxyl groups surround a sodium ion. The tivity. This method has yielded thousands of antib- alkyl groups are oriented toward the outside of the otic substances, of which hundreds have been complex, and the polar oxygens and the metal ion developed into effective drugs. Antibiotics are, by are on the inside The hydrocarbon like surface of definition, toxic(anti="against" bios="life"), and the complex permits it to carry its sodium ion the goal is to find substances that are more toxic to through the hydrocarbon-like interior of a cell mem- infectious organisms than to their human hosts. brane. This disrupts the normal balance of sodium Since 1950, a number of polyether antibiotics ions within the cell and interferes with important have been discov ered using fermentation technol- processes of cellular respiration. Small amounts of ogy. They are characterized by the presence of sev- monensin are added to poultry feed in order to kill eral cyclic ether structural units, as illustrated for the parasites that live in the intestines of chickens. Com- case of monensin in Figure 16.3a. Monensin and pounds such as monensin and the crown ethers that other naturally occurring polyethers are similar to affect metal ion transport are referred to as crown ethers in their ability to form stable complexes ionophores ("ion carriers") H CH CH3 OH HOCH,IO OCH OH HHH CH2 H CH CH COH (a) CH, CH H H H3 CH CH FIGURE 16.3(a)The structure of monensin; (b) the structure of the monensin-sodium bromide complex showing coor dination of sodium ion by oxygen atoms of monensin. Back Forward Main MenuToc Study Guide ToC Student o MHHE Website624 CHAPTER SIXTEEN Ethers, Epoxides, and Sulfides POLYETHER ANTIBIOTICS One way in which pharmaceutical companies search for new drugs is by growing colonies of microorganisms in nutrient broths and assay￾ing the substances produced for their biological ac￾tivity. This method has yielded thousands of antibi￾otic substances, of which hundreds have been developed into effective drugs. Antibiotics are, by definition, toxic (anti  “against”; bios  “life”), and the goal is to find substances that are more toxic to infectious organisms than to their human hosts. Since 1950, a number of polyether antibiotics have been discovered using fermentation technol￾ogy. They are characterized by the presence of sev￾eral cyclic ether structural units, as illustrated for the case of monensin in Figure 16.3a. Monensin and other naturally occurring polyethers are similar to crown ethers in their ability to form stable complexes with metal ions. The structure of the monensin– sodium bromide complex is depicted in Figure 16.3b, where it can be seen that four ether oxygens and two hydroxyl groups surround a sodium ion. The alkyl groups are oriented toward the outside of the complex, and the polar oxygens and the metal ion are on the inside. The hydrocarbon-like surface of the complex permits it to carry its sodium ion through the hydrocarbon-like interior of a cell mem￾brane. This disrupts the normal balance of sodium ions within the cell and interferes with important processes of cellular respiration. Small amounts of monensin are added to poultry feed in order to kill parasites that live in the intestines of chickens. Com￾pounds such as monensin and the crown ethers that affect metal ion transport are referred to as ionophores (“ion carriers”). C H O CH3 CH3 HOCH2 OH H H O CH3 H O H CH3 O CH2 CH3 H O O CO2H CH3 OCH3 CH3 CH3 CH3 CH3 O OH O H O H O Na H CH3 H O CH3CH2 H H3C O O HO CH3 CH3 O OCH3 Br CH3 (a) (b) FIGURE 16.3 (a) The structure of monensin; (b) the structure of the monensin–sodium bromide complex showing coor￾dination of sodium ion by oxygen atoms of monensin. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website