Bioassay-guided fractionation of the EtOAc extract of the roots of Thai Ziziphus oenoplia var. brunoniana resulted in the isolation of four new 13-membered cyclopeptide alkaloids of the 5(13) type, ziziphine N-Q. The structures of the new metabolites were elucidated on the basis of spectroscopic analyses and the stereochemical assignments were established by comparison with other related compounds of known stereochemistry. Ziziphine N and Q exhibited significant antiplasmodial activity against the parasite Plasmodium falciparum with the inhibitory concentration (IC50) values of 3.92 and 3.5 mug/mL, respectively. Ziziphine N and Q also demonstrated weak antimycobacterial activity against Mycobacterium tuberculosis with the same MIC value of 200 mug/mL. (C) 2004 Elsevier Ltd. All rights reserved.