Two new pyrrolidine alkaloids, pandamarilactonine-C and -D, were isolated from Pandanus amaryllifolius. Based on the total synthesis of pandamarilactonine-C and its related alkaloid, pandamarilactonine-A, the relative stereochemistry of pandamarilactonine-A and -B, which was previously proposed by spectroscopic analysis, was revised.Key words pyrrolidine alkaloid; Pandanus; pandamarilactonine; total synthesis; structure elucidation; structure revisionThe genus Pandanus (Pandanaceae) comprises approximately 600 species that are widely distributed in tropical and subtropical regions. Several Pandanus species are used as a remedy for toothache and rheumatism, and as diuretic, cardiotonic, etc.1) In a recent pharmacological screening, the hypoglycemic effect of an extract of P. odorus was noted.2-4) In our continuing search for structurally unique and biologically active Pandanus alkaloids, new pyrrolidine alkaloids were found in P. amaryllifolius ROXB.5-7) Further investigation of the minor constituents in the fresh leaves of this plant resulted in the isolation of two new alkaloids, pandamarilactonine-C and -D (1, 2). In this communication, we describe the structure elucidation of these alkaloids as well as the total synthesis of pandamarilactonine-C (1) and its related alkaloid, pandamarilactonine-A (3), which resulted in the revision of the relative stereochemistry of pandamarilactonine-A and -B (3, 4), which was previously proposed based on the results of spectroscopic analysis.The crude alkaloid fraction (1.10 g), which was obtained from young leaves of P. amaryllifolius, 5) was initially separated by SiO 2 column chromatography using MeOH/CHCl 3 gradient, and then the 2-5% MeOH/CHCl 3 eluate was subjected to SiO 2 medium pressure liquid chromatography using 2% EtOH/CHCl 3 to give 20 mg of pandamarilactonine-C and 4 mg of pandamarilactonine-D.The two new compounds, pandamarilactonine-C (1) 8) and pandamarilactonine-D (2), 9) gave respectively m/z 318.1691 [MϩH] ϩ and m/z 318.1704 [MϩH] ϩ by high-resolution FAB-MS, which established the molecular formulas of the two compounds as C 18 H 23 NO 4 , and indicated that these are isomers of coexisting alkaloids, pandamarilactonine-A and B.5) The UV, 1 H-and 13 C-NMR spectra of pandamarilactonine-C and -D were very similar to those of pandamarilactonine-A and B, which comprised g-butylidene-a-methyl a,bunsaturated g-lactone and pyrrolidinyl a,b-unsaturated glactone residues, indicating that these four alkaloids are stereoisomers. Unambiguous assignment of all the carbons and protons in 1 8) and 2 9) was realized using 1 H-1 H correlated spectroscopy (COSY), heteronuclear multiple quantum coherence (HMQC), and heteronuclear multiple bond correlation (HMBC) spectra. Comparing the 13 C-NMR data of 1 and 2 with those of 3 and 4, 5) a significant difference was observed in the chemical shifts at the C-4 position. The signals of 1 (d 130.3) and 2 (d 133.9) appeared in the higher field than those of 3 (d 137.7) and 4 (d 137.7), which can be reasonably interpreted in term...