Glycopentanolones A-D, four new geranylated quinolone alkaloids from Glycosmis pentaphylla

The ethanolic extract obtained from the stems of Glycosmis pentaphylla was found to suppress antigen-mediated degranulation of rat basophilic leukemia (RBL-2H3) cells. Four new geranylated 2-quinolone alkaloids, named glycopentanolones A-D (1-4), and 12 known metabolites (5-16) were isolated from the ethanolic extract from the stems of G. pentaphylla using bioassay-guided fractionation. Their structures were elucidated by a combination of 1D and 2D NMR, and HRESI-MS. The inhibitory effects of the isolated constituents on β-hexosaminidase release from RBL-2H3 cells were examined, and compounds 1, 5, 8 and 11 exhibited potent inhibitory activity with IC₅₀ values between 0.05 and 4.28 μM.