Triterpenes possessing an unprecedented skeleton isolated from hydrolyzate of total saponins from Gynostemma pentaphyllum

Five novel Triterpenes were isolated from hydrolyzate of total saponins from Gynostemma pentaphyllum and identified as gypensapogenin A (1), gypensapogenin B (2), gypensapogenin C (3), 3-O-β-d-glucopyranosyl-gypensapogenin D (4) and gypensapogenin D (5), two of which (1 and 2) possess unprecedented ring A. The cyclization of the side chains-3 formed five-membered cyclic ketone rings similar to ring E in 1. The 21-oic acid-21, 23-lactone was present in the side chains of 4 and 5. We also proposed the possible formation mechanisms of compounds 1-3. Compounds 1-5 were evaluated for cytotoxic activities in three cell lines including A549, U87 and Hep3B and compound 3 showed significant activities toward A549 and U87 human Cancer cells (with IC 50 values at 0.11 and 0.58 μm respectively).