Hunzeylanines A–E, Five Bisindole Alkaloids Tethered with a Methylene Group from the Roots of Hunteria zeylanica

Five novel bisindole alkaloids, hunzeylanines A–E (1–5), with an unprecedented skeleton were isolated from the roots of Hunteria zeylanica. Compounds 1–5 represent the first examples of akuammine–pleioarpamine-type bisindole alkaloids fused with a dihydropyran unit. Their structures including absolute configurations were established through comprehensive spectroscopic data analyses and computational calculation methods. The plausible biogenetic pathway of 1 was also proposed. Alkaloids 1 and 2 displayed moderate cytotoxicity toward three human cancer cell lines (MDA-MB-231, AV3, and Huh7).