A direct method for assignment of absolute configurations in crown gall metabolites: the structure of nopaline.

The absolute configurations of the crown gall tumor metabolite nopaline (1a) have been determined by a direct degradative method. Oxidation of nopaline with KMnO4 afforded (S)-arginine and (R)-glutamic acid. Separation of these two amino acids was accomplished easily and simultaneously with determination of chirality by chromatography on a reverse-phase column eluted with chiral eluent. The present technique can easily determine absolute configurations on submilligram quantities. In contrast, an attempted determination of absolute configuration by synthesis from (S)-arginine and chiral 2-chloropentanedioic acid was unsuccessful.