Picrotoxane sesquiterpene and α-pyrone derivative from Dendrobium signatum and their free radical scavenging potency.

One new picrotoxane sesquiterpene (1) and one new α-pyrone derivative (4), together with nine known compounds, were isolated from the aerial parts of Dendrobium signatum. The structures of the new compounds were elucidated based on the interpretation of 1D and 2D NMR, HRESIMS and electronic circular dichroism (ECD) data. The absolute configuration of 1 was confirmed by single-crystal X-ray diffraction data. The new α-pyrone 4 exhibited promising ABTS scavenging activity with IC50 value of 0.7 μM.