Configurational Reassignment of (+)‐Polycitorol A and (−)‐Polycitorol B by Nuclear Magnetic Resonance Spectroscopic Analysis, Theoretical Calculation, and Total Synthesis

The proposed structures of (+)‐polycitorol A and (−)‐polycitorol B, marine tricyclic alkaloids, have been questioned by Kim et al. through total synthesis. In this study, the structure of polycitorol A, a perhydropyrrolo[2,1‐ j ]quinoline derivative, was scrutinized by nuclear magnetic resonance (NMR) spectroscopic analysis and theoretical calculation. DP4+ analysis of the density functional theory‐calculated NMR chemical shifts showed that the proposed structure most likely required configurational reassignment at the C2 and C5 positions. The reassigned structure of (+)‐polycitorol A was finally established through total synthesis. Inspired by known interconversion between cylindricines A and B through an aziridinium ion, a ring‐expansion reaction of (+)‐polycitorol A under Cossy conditions led to (−)‐polycitorol B. The stereochemistry of (+)‐polycitorol A and (−)‐polycitrol B corresponded to that of (−)‐fasicularin.