Complement-Inhibiting Cucurbitacin Glycosides from Picria fel-terrae

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Abstract
Four cucurbitacin glycosides were isolated from Picria fel-terrae and identified by MS and NMR spectroscopy as picfeltarraenin IA (1), picfeltarraenin IB (2), picfeltarraenin IV (4), and a new compound picfeltarraenin VI (3) (picfeltarraegenin I 3-O-β-d-xylopyranoside). All four compounds acted as inhibitors on both the classical and alternative pathways of the complement system, with compound 3 exhibiting the highest inhibitory activity (IC50 29 ± 2 μM and 21 ± 1 μM, respectively). Compounds 1−4 showed no antiviral, antibacterial, or antifungal activities. Picfeltarraenin IA and IB were tested in an in vitro human tumor cell line panel, but displayed no cytotoxic activity.