Anion recognition by thiostrepton

A bicyclic polypeptide antibiotic thiostrepton forms both 1:1 and 1:2 compl exes with anions (as tetrabutylammonium salts) in organic solvents with K-2 > K-1 for F- and K-2 <<K-1 for all other anions studied. Relative stabilit ies of 1:1 complexes in DMSO are AcO- similar to F- >> Cl-, Br-, HSO4-, H2P O4-, but in CHCl3 they follow a different order: Cl- similar to HSO4- > F- similar to AcO- > Br- > H2PO4-. The binding mode of anions to thiostrepton is discussed on the basis of solvent effects on the complexation selectivit y. (C) 2001 Elsevier Science Ltd. All rights reserved.