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

(±)-Uncarilins A and B (1a/1band 2a/2b), two pairs of unusual dimeric isoechinulin-type enantiomers with a symmetric four-membered core, were isolated from Uncaria rhynchophylladriven 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 MT1and MT2receptors with agonistic rates of 11.26% and 52.44% at a concentration of 0.25 mM.