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).