The Crystal and Molecular Structure of Pikromycin

Abstract

Abstract The detailed molecular geometry of pikromycin (C28H47NO8) has been examined by means of X-ray crystal analysis. The crystals are orthorhombic, with four molecules in a unit cell with dimensions of a=11.295, b=25.734, and c=10.509 Å; the space group is P212121. 2259 unique intensity data were collected on a four-circle diffractometer with graphite-monochromated Cu Kα radiation. The structure was solved by the Monte Carlo direct method, using the 30 strongest reflections as the starting set; the 215th random phase set led to the correct solution. The R value reached 0.056 by block-diagonal least-squares refinements. The conformation of the fourteen-membered macrolide ring is considerably different from that of (p-bromobenzoyl) pikromycin in the solid state; e.g., the C=C and C=O conjugated double bonds are cisoid in pikromycin, while they are transoid in the derivative. The molecules are held together through two kinds of intermolecular hydrogen bonds, forming a three-dimensional hydrogen-bonded structure.