Configurational Analysis of Tetracyclic Dimeric Pyrrole-Imidazole Alkaloids using a Floating Chirality Approach

摘要

The structure elucidation of the palau'amine congener tetrabromostyloguanidine (>1), which used interproton distances from ROESY spectra as restraints in a computational approach, the so-called fc-rDG/DDD method, led to a revision of the relative configuration of palau'amine (>2) and its congeners in 2007. The recent total synthesis of (±)-palau'amine (>2) subsequently confirmed the computed structural revision of the relative configuration. In order to test a broader application range of the fc-rDG/DDD method, the present study investigated two additional dimeric pyrrole-imidazole alkaloids, axinellamine A (>3) and 3,7-epi-massadine chloride (>4). These calculations allowed the simultaneous assignment of the relative configuration for all eight stereogenic centers of compounds >3 and >4 without using any information from the reported configurations. In contrast to the palau'amine congeners, the fc-rDG/DDD method confirmed the relative configuration originally described for axinellamine A (>3) and 3,7-epi-massadine chloride (>4).