Isolation and identification of an antiparasitic triterpenoid estersaponin from the stem bark of Pittosporum mannii (Pittosporaceae)

To screen for antiparasitic properties of Pittosporum mannii Hook (Pittosporaceae) through in vitro bioassay tests and to identify the bioactive compound(s). The stem bark of Pittosporum mannii was harvested in Bali Nyonga in January 2007. The CH2Cl2 and MeOH extracts were tested in vitro for antiparasitic activity. NF54 (an airport strain of unknown origin and sensitive to all known drugs) and K1 (a clone originating from Thailand and resistant to chloroquine/pyrimethamine) strains were used for the antiplasmodial screening while Leishmania donovani MHOM-ET-67/L82 was used for antileishmanial testing. 1H and 13C NMR spectra were recorded on a Bruker AMX-500 spectrometer using CDCl3 as solvent. EIMS were recorded on a double-focusing mass spectrometer (Varian MAT 311A) while HREIMS were recorded on a JEOL HX 110 mass spectrometer. The MeOH extract was active on both the chloroquine-resistant (K1) strain (IC50=4.3 μg/mL) and on the macrophages of Leishmania donovani (IC50=8.6 μg/mL). The CH2Cl2 extract was considered inactive on both parasites (IC50>5.0 μg/mL and 21.7 μg/mL respectively). Compound 1, a constituent that precipitated from the MeOH extract, showed pronounced activity on both Plasmodium falciparum and Leishmania donovani parasites (IC50=1.02 and 1.80 μg/mL respectively) with artemisinin and miltefosine included as reference drugs. Its structure was identified as 1-O-[apha-L-(Rhamnopyranosyl]-23-acetoxyimberbic acid 29-methyl ester, a pentacyclic triterpenoid estersaponin. The present study constitutes the first report on the antiparasitic activity of this plant and provides some support for the traditional use of the plant in the treatment of malaria. The plant has therefore been identified as a potential source for the discovery of antiparasitic lead compounds.