The crystal structure of the antibiotic hedamycin (1) has been solved by direct method and refined by least squares techniques to R=0.091 for 2289 of 2643 independent reflexions. Crystals of C4,HS,,N,0 are orthorhombic, space group P2,2,2' with lattice parameters a=24.239 (12), b=21.440 (lo), c=7.369 (4) A, Z = 4. The structural features of hedamycin derived earlier by chemical and spectroscopical means are confirmed. Optical rotation and circular dichroism indicate that hedamycin (1) has the absolute configuration of the related antibiotic kidamycin (3). The conformation of ring F is a chair form with the aryl substituent almost axial. The bioxirane part of the antibiotic is in a synclinal conformation.
Introduction. -The structure of the antitumor antibiotic hedamycin (1) has recently been elucidated by chemical and spectroscopic means (cf. [ l ] and ref.
therein). The relative configurations in the two tetrahydropyran rings E and F on the one hand, and in the diepoxide side chain on the other hand were also determined. It was not possible, however, to derive the relative configuration of the side chain with respect to rings E and F, nor to determine the absolute configuration of the whole molecule.
A crystal structure analysis seemed to be the best means to fill these gaps and yield additional insight into conformational aspects of hedamycin and related compounds. We were not able to prepare a suitable heavy atom derivative, but hedamycin itself could be crystallized from chloroform/heptane in a form suitable for X-ray structure determination.
Results and discussion. -The X-ray structure determination revealed the molecular structure shown in Figure (the figure does not give the absolute configuration). Structural features that had been determined by chemical and spectroscopic means [2] [3] are confirmed, including the unique diepoxide side chain and the relative configurations within this particular fragment [ 11.