Seco-neferine A–F, three new pairs of benzyltetrahydroisoquinoline alkaloid epimers from Plumula Nelumbinis and their activity

Three new pairs of benzyltetrahydroisoquinoline (BIQ) alkaloid epimers, Seco-neferine A-F (1–6), were isolated from an EtOH extract of Plumula Nelumbinis. The structures of these compounds were identified by a combination of NMR, HR-ESI-MS, circular dichroism, UV spectroscopic analyses and specific rotations. The structure of compounds 1–6 possesses high similarity with neferine, because these three pairs of epimers have the same skeleton as neferine. Compounds 1,2 and 5,6 are open-loop compounds of position 1′ and 1 of neferine respectively. The H connects with position 2′ N of compounds 1,2 is replaced by methyl, forming the structure of compounds 3,4. Moreover, six compounds were tested for cytotoxicity against MDA-MB-231 breast cancer cell. Compound 6 displayed moderate inhibitory effects on breast cancer with IC50 of 38.96 μM, while compounds 2,3,4 show certain inhibitory effects.