From the CH2Cl2 extract of the root bark of Z. mucronata (Rhamnaceae), a new cyclopeptide alkaloid, named mucronine J, was isolated together with previously known alkaloids abyssenine A and mucronine D. The structure of mucronine J was elucidated by mass spectrometry and 1D and 2D NMR. A solution conformation is proposed on the basis of NOE experiments in combination with MM2 calculations.