Isolation and absolute configuration determination of alkaloids from Pandanus amaryllifolius

Seven new alkaloids belonging to three typical classes, isolated from an ethanolic extract of Pandanus amaryllifolius, were applied to establish the models in structural elucidation. The first type [pandanusines A and B (1 and 2)] was applied to alkaloids with a diazaspirocyclic ring system. The absolute stereochemistry of aminal carbon is determined by analysis of J-based configuration analysis and circular dichroism spectroscopy, which has never been revealed before. The second type [pandalizines C–E (3–5)], the stereochemistry of unusual indolizinone with chiral hydroxyl substitutions were determined by circular dichroism spectroscopy and vibrational circular dichroism experiments. The last type [norpandamarilactonines C and D (6 and 7)], a comparing model in determination of diastereomers of pyrrolidinyl α,β-unsaturated γ-lactone alkaloids was established. Our study provides solutions for a challenging subject in stereochemistry determination for three different types of Pandanus alkaloids.