Studies on the lonophorous antibiotics. Part IV. Crystal and molecular structure of the thallium salt of lonomycin

Abstract

Lonomycin (I) is an antibiotic produced by Streptomyces ribosidicus. The crystal and molecular structure of its thallium salt has been established by a three-dimensional X-ray analysis by the heavy-atom method from diffractometer data. Crystals are orthorhombic, space group P2₁2₁2₁, a= 16.257(2), b= 25.731(4), c= 12.502(2)Å, Z= 4. The structure was refined by block-diagonal least-squares to R 0.075 for 3 225 reflections. The lonomycin molecule contains six ring systems: three five-membered rings have an envelope conformation, while the other three are six-membered and adopt a chair conformation. The molecule as a whole takes a circular conformation and the thallium ion is located in a cavity.