Structurally Diverse Indole Alkaloids with Vasorelaxant Activity from Melodinus hemsleyanus.
2020
Six new structurally diverse indole
alkaloids, melohemsines J–M
(1–4), 11-hydroxy-Δ14-vincamine (5), and 11-hydroxy-16-epi-Δ14-vincamine (6), and 15 known alkaloids
were isolated from the leaves and twigs of Melodinus hemsleyanus Diels. These new compounds and their absolute configurations were
determined through spectroscopic data analyses, X-ray diffraction,
and computational methods. Melohemsine J (1) is the first
example of a melodinus-type alkaloid possessing a 6/6/5/5/6/5 hexacyclic
skeleton and containing a tetrahydrofuro[2,3-b]pyridine-2(3H)-one unit. Melohemsine K (2) is an unusual
aspidosperma-type alkaloid possessing a 6/5/6/5/5 pentacyclic architecture
with a contracted E ring (loss of CH2). Compounds 5–10 and 16 exhibited vasorelaxant
activities with EC50 values of 0.8–3.8 μM.
In addition, compound 4 displayed moderate cytotoxicity
toward the tumor cell lines HepG2 and A-549 with EC50 values
of 18.7 and 28.7 μM, respectively.
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