Novel Triterpenoid Alkaloids With Their Potential Cytotoxic Activity From the Roots of Siraitia grosvenorii

Four novel triterpenoid alkaloids, siragrosvenins A-D (1-4), and two new cucurbitane-type triterpenoids, siragrosvenins E-F (5, 6), together with eight known analogs (7-14), were isolated from the roots of Siraitia grosvenorii. Compounds 1-4 possessed a rare cucurbitane-type triterpenoid scaffold, featuring an extra pyrazine unit via the Strecker reaction in the cucurbitane framework. Compound 5 displayed a 6/6/6/5/6/5-fused polycyclic ring system, with an uncommon fused furan and pyran ring in the side chain. All the structures were characterized by extensive spectroscopic analysis, including HRESIMS, NMR, and X-ray crystallographic data. It is worth noting that the DP4⁺ analysis method was applied for the first time to determine the absolute configurations of the trihydroxybutyl moiety in the side chain of compounds 1-4. In vitro cytotoxicity screening found that compounds 4, 8, 9, 13, and 14 exhibited remarkable cytotoxic activities against three cell lines with IC₅₀ values ranging from 1.44 to 9.99 μM. Siragrosvenin D shows remarkable cytotoxic activity on MCF-7 cells. As a result, it inhibited the proliferation of MCF-7 cells and reduced their viability via the induction of G2/M phase arrest and significantly induced apoptosis in MCF-7 cells.