DNA-BINDING ANTIBIOTICS - X-RAY STRUCTURE OF THE DISTAMYCIN A ANALOG

The crystal structure of the antibiotic distamycin A analog containing two pyrrol carboxamide fragments has been determined. The space group of the crystals is P21 b; the unit-cell dimensions are a = 11.169, b = 21.535, c = 7.863 A ̊, α = β = 90°, γ = 122.45°, Z = 4. The structure is solved by direct methods, and refined with the full-matrix least-squares procedure. The data on the structure of the pyrrol carboxamide backbone allow the following conclusions to be made about the molecular structure of the distamycin type antibiotics: (i) the amide groups have normal trans-configuration with slightly shortened C-C and C-N bonds adjacent to the pyrrol rings, (ii) the N-methyl groups of the pyrrol rings and the oxygen atoms of the amide groups have the same orientation with respect to the backbone. In the distamycin A analog molecule the pyrrol rings and amide group between them are approximately coplanar. © 1979.