Taraxastane and Lupane Triterpenoids from the Bark of Manilkara zapota

Aims: Discovering new lead compounds against cancer and bacterial infections is a crucial step to ensuring a sustainable global pipeline for new effective drugs. This study focus on the isolation of secondary metabolites of methanol extract from the bark of Manilkara zapota (Sapotaceae) a Cameroonian medicinal plant.

Study Design: According to the literature, plants of the genus Manilkara are potential sources of antibacterial and anticancer secondary metabolites.

Methodology: The air-dried and powdered bark (4.0 kg) of M. zapota was extracted at room temperature for 72 h with a methanol. The extract was concentrated to dryness under vacuum and the residue was subjected to repeated column chromatographic separation. The structures of the isolates were established by means of spectroscopic methods. These compounds were screened in vitro for their activity against bacterial and human Caucasian prostate adenocarcinoma cell line PC-3.

Results: Two new pentacyclic triterpenoids, 3-acetyltaraxer-14-en-12-one (1) and 3-hydroxy-7-oxolup-20(29)-en-28-oic acid (4), together with eleven known compounds were isolated from the methanol extract from the bark of Manilkara zapota. The structures of all compounds were determined by comprehensive analyses of their 1D and 2D NMR, mass spectral (EI and ESI) data and comparison with previously known analogs. The agar diffusion test delivered low to missing antimicrobial activities, corresponding with MICs > 1mg/ml. In addition, compounds 1, 4-7, 11 and 12 displayed moderate cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3 with IC50 value ranging from 14.1-30.6 mg/ml, while compounds 2 and 3 showed weak cytotoxic activity with an IC50 value of 61.2-62.5 mg/ml, compared to the standard doxorubicin (IC50 = 0.9 µg/ml).

Conclusion: Two new triterpenoids were isolated, some isolated compounds displayedmissing or low activities against bacterial, plant pathogen oomycetes and moderate cytotoxic activity against the human Caucasian prostate adenocarcinoma cell line PC-3.