(±)-Uncarilins A and B, Dimeric Isoechinulin-Type Alkaloids fromUncaria rhynchophylla

(±)-Uncarilins A and B ( 1a / 1b and 2a / 2b ), two pairs of unusual dimeric isoechinulin-type enantiomers with a symmetric four-membered core, were isolated from Uncaria rhynchophylla driven by LCMS-IT-TOF analyses. Their structures were elucidated by extensive 1D and 2D NMR spectra, X-ray diffraction, and ECD spectroscopic data. (−)-Uncarilin B ( 2a ) showed activities on MT 1 and MT 2 receptors with agonistic rates of 11.26% and 52.44% at a concentration of 0.25 mM.