Isolation and structural characterization of polycyclic diazepine alkaloids from Pandanus yvanii

Four unprecedented polycyclic alkaloids, designated pandazepines A-D (1-4), featuring rare diazepine-containing frameworks, were isolated from the leaves of Pandanus yvanii. Their structures were elucidated through comprehensive spectroscopic analyses. Pandazepines A and B (1 and 2) represent the first examples of tetracyclic pyrrolidinoindoline-1,3-diazepine alkaloids, with their absolute configurations established by comparison of experimental and TDDFT-calculated ECD spectra. Pandazepines C and D (3 and 4) possess unprecedented pentacyclic fused-ring systems comprising linearly fused 1,3-diazepine, γ-lactam, and indolizidine units. The relative configurations of 3 and 4 were determined through GIAO NMR chemical shift calculations in combination with DP4+ probability analysis. A putative biosynthetic pathway for 1-4, originating from putrescine is proposed. Collectively, these findings expand the structural diversity of diazepine-containing natural products and provide new insights into the biosynthetic capabilities of the Pandanus genus.