Two new alkaloids, both possessing a pyrrolidinyl alpha,beta-unsaturated gamma-lactone residue and a gamma-alkylidene alpha,beta-unsaturated gamma-lactone residue, were isolated from a tropical medicinal plant, Pandanus amaryllifolius Roxb. Their structures were deduced by spectroscopic analysis including the new NMR technique PFG J-HMBC 2D spectroscopy and then confirmed by biomimetic total synthesis. It was found that one diastereoisomer, pandamarilactonine-A (1), comprised a mixture enriched with (+)-enantiomer, while another diastereomeric isomer, pandamarilactonine-B (2), occurred as a racemate.