The Crystal and Molecular Structure of Staurosporine, a New Alkaloid from a Streptomyces Strain

The molecular sturcture of staurosporine, an alkaloid from a Streptomyces strain, has been determined by means of an X-ray crystallographic analysis of its methanol solvate (C28H26N4O3·CH3OH). The crystals are monoclinic, with four formula units in a unit cell with dimensions of a=23.487(6), b=7.636(3), c=15.638(4) Å, and β=116.71(5)°; the space group is C2. 2532 unique intensity data were collected on a four-circle diffractometer with LiF-monochromated Cu Kα radiation. The structure was solved by the Monte Carlo direct method, using the 20 strongest reflections as the starting set; the 72nd random phase set led to the correct solution. The R value reached 0.047 by block-diagonal least-squares refinements. Staurosporine has been found to contain a unique dimeric indole structure. Because of the steric hindrance, the indolo[2,3-a]carbazole aromatic system in the molecule is slightly bent; the two terminal benzene rings make an angle of 7.5° with each other.