Chemistry of micrococcin P. Part IX. The crystal and molecular structure of micrococcinic acid bis-4-bromoanilide

Abstract

The structure of dimethyl micrococcinate, C₂₄H₁₇N₅O₅S₄, in the form of its bis-4-bromoanilide, C₃₄H₂₁Br₂N₇O₃S₄, has been determined by three-dimensional X-ray crystal structure analysis. The crystals are monoclinic, with unit cell dimensions a= 22·46, b= 43·23, c= 7·87 Å, β= 95° 25′, and space group P2₁/a. The solution of the crystal structure has shown that these crystals contain two molecules of micrococcinic acid bis-4-bromoanilide and one molecule of anisole (the solvent of crystallisation) per asymmetric unit. The main features of the structure were determined by successive three-dimensional Fourier syntheses, following the initial placing of two of the four bromine atoms from the Patterson synthesis. Block diagonal least-squares refinement of the atomic parameters reduced the usual R index to 0·120.

The result of this analysis confirms and extends the structural deductions based on the chemical investigations of dimethyl micrococcinate; it shows conclusively that the molecule consists of an extended heterocyclic ring system, with three of the four thiazole rings bonded directly to the pyridine nucleus. The two 2,4′-linked thiazole rings are coplanar within the limits of accuracy of this determination.

The two molecules in the asymmetric unit are chemically identical and are related by an approximate noncrystallographic two-fold axis. There does not appear to be any specific intermolecular bonding between the two molecules, and the crystal structure with the non-crystallographic two-fold axis is a consequence of the packing of these long irregular molecules. There are minor conformational differences between the two independent molecules.