THE CRYSTAL AND MOLECULAR STRUCTURE OF CHALCOMYCIN. J. Ronald Rubin, Peter W. K. Woo, Parke-Davis Pharmaceutical Research Division of Warner Lambert Comany 2800 Plymouth Road, Ann Arbor, MI. 48105

Chalcomycin (C₃₅H₅₆O_l4, F.W.=700.8) is a macrolide antibiotic produced by Streptomyces bikiniensis. It is a member of the 16-membered macrolide ring antibiotic family and is unique in containing the sugars [[beta]]-chalcose and [[beta]]-mycinose. Colorless needles of the antibiotic were obtained from ethanol solutions. The unit cell parameters and x-ray diffraction data were measured on a CAD-4 diffractometer using CuK[[alpha]] radiation. The crystals are monoclinic, space group P2₁, with unit cell parameters, a=8.965(3),b=22.989(9), c=9.280(2) Å and [[beta]]=90.78(3)deg.. The unit cell of V=1913 ų contains two molecules of the antibiotic. A total of 1557 unique reflections were measured using the omega scan technique. The structure was solved using direct methods using the SIR-92 programs and refined to an unweighted R-factor of 0.068. The conformation of the macrolide ring and the two glycosidic sugar residues is roughly planar. The molecule has opposing hydrophilic and hydrophobic surfaces. By extension from the known chirality of the sugar residues the configuation of all of the chiral centers was determined.