Rhynchophylline

Rhynchophylline is an alkaloid found in certain Uncaria species (Rubiaceae), notably Uncaria rhynchophylla and Uncaria tomentosa. It is a non-competitive NMDA antagonist (IC50 = 43.2 microM) and calcium channel blocker. It also occurs naturally in the leaves of the Mitragyna speciosa (Kratom) tree (also a Rubiaceae), native to Thailand.