Discovery and Biomimetic Semisynthesis of Spirophyllines A–D from Uncaria rhynchophylla

Spirophyllines A-D (-), four new spirooxindole alkaloids all characterized by the spiro[pyrrolidin-3,3'-oxindole] core and a rare isoxazolidine ring, were isolated from . Their structures were determined by spectroscopic methods and confirmed by X-ray crystallography. Based on the biomimetic semisynthesis strategy, compounds - were synthesized in three steps via the key reactions of 1,3-dipolar cycloaddition and Krapcho decarboxylation from corynoxeine. Interestingly, compound showed moderate inhibitory activity against the K1.5 potassium channel (IC = 9.1 μM).