A New Bis-indole Alkaloid, Spermaocymine A, and an Anthraquinone from Spermacoce ocymoides

A phytochemical study on Spermacoce ocymoides has led to the isolation of a novel bis-indole alkaloid,
spermaocymine A (2), together with the known alkaloid 4-methyl-borreverine (1), as well as an anthraquinone, 8-hydroxy-2-(hydroxymethyl)-1-methoxyanthracene-9,10-dione (3). The structures of the isolated
compounds were elucidated by analyzing spectroscopic and spectrometric data, including one-dimensional
(1D)- and 2D-NMR and high resolution (HR)-MS. Newly isolated alkaloid 2 was a C-3,14-stereoisomer of 1,
the first natural stereoisomer of related bis-indoles containing an indeno[1,2-b]indole skeleton with an epiminoethano bridge. When 1–3 were assayed against five tumor cell lines including multi-drug resistant cells,
compound 1 exhibited potent antiproliferative activity with IC50 values of 6.2–11.5 µM.
Key words Spermacoce ocymoides, bis-indole alkaloid, anthraquinone, antiproliferative activity