Nudicaulins, Yellow Flower Pigments of <i>Papaver nudicaule</i>: Revised Constitution and Assignment of Absolute Configuration

The constitution of the aglycon of nudicaulin has been revised to be a pentacyclic indole alkaloid. The relative and absolute configurations of the two diastereomers, nudicaulins I (<b>3a</b>) and II (<b>3b</b>), have been assigned by NMR, conformational analyses, and interpretation of the experimental ECD spectra by quantum-chemical calculations.