The Absolute Configuration of Natural (-)-Stercobilin and Other Urobilinoid Compounds
- Hans Brockmann, Jr.*,
- Gerrit Knobloch*,
- Hans Plieninger†,
- K. Ehl†,
- J. Ruppert†,
- Albert Moscowitz‡, and
- C. J. Watson§
- *Gesellschaft für Molecularbiologische Forschung, D-3301 Stöckheim über Braunschweig, Mascheroder Weg 1, Germany
- †Organisch-Chemisches Institut der Universität, D-69 Heidelberg, Germany
- ‡Department of Chemistry, University of Minnesota, Minneapolis, Minn. 55455
- §University of Minnesota Medical Research Unit, Northwestern Hospital, Minneapolis, Minn. 55407
Abstract
Chromic acid degradation of natural (-)-stercobilin (1) yields 2(R)-methyl-3(R)-ethylsuccinimide (+2), whereby the absolute configuration of 1 at the chiral centers C-1, C-2, C-7, and C-8 is established. The substituted oxo-tetrahydrodipyrromethane precursor, 5, for the total synthesis of (-)-stercobilins 3 and 4, in which the relative configuration between the asymmetric centers is known, yields 2(S)-methyl-3(S)-ethylsuccinimide (-2) under the same conditions of degradation. Nuclear magnetic resonance studies of 1 and 3 show that in 1 the hydrogen atoms at C-2 and C-2′, as well as those at C-7 and C-7′, are trans relative to one another. Accordingly, natural (-)-stercobilin possesses the 2′(S), 7′(S) configuration, and has the configuration formula 6(1 (R), 2(R), 2′(S), 7′(S), 7(R), 8(R)). These results, coupled with those of earlier studies, also establish the absolute configuration of the (+)-urobilin 7 and of the phycobilin 8 at C-7′.
