Antimicrobial activity of phenolic triterpenes from Maytenus cuzcoina

The aromatic triterpenoids constitute a small group of unsaturated and oxygenated D:A-friedo-nor-oleananes restricted to the plant family Celastraceae, and they are of medical interest since they tend to exhibit antibiotic and anticancer activities [1].

As part of our studies on medicinal plants belonging to this family, which is widely used as folk medicine in South and Central America, we had previously reported on dihydro-β-agarofuran sesquiterpenes as multidrug-resistence inhibitors and anti-tumor promoters [2] from Maytenus cuzcoina, a plant endemic to the Cusco region, Peru.

A further search for structurally interesting and bioactive compounds from this plant resulted in the isolation of six known phenolic triterpenes in addition to the new compounds, 21β-hydroxycuzcoinol (1), cuzcoinol (2), 6β-(2-oxo-propyl)-pristimerol (3), and 6α,7α-isopropylidendioxo-blepharodol (4). Their structures were determined by spectroscopic methods, including ¹H-¹³C (HSQC and HMBC), and ROESY NMR experiments.

The compounds were assayed for antimicrobial activity against Gram-positive and Gram-negative bacteria, and the yeast Candida albicans. Compound 3 and 6-deoxoblepharodol exhibited the highest activity against Bacillus subtilis (MIC 5–10µg/ml), while compound 10 showed a moderate activity against B. cereus and Staphylococcus epidermidis (CMI 10–20µg/ml). The structure-activity relationship established the relevance of the substituents on B ring for the antimicrobial activity.

Acknowledgments: This work has been supported by the Spanish Grant CTQ-2006–13376/BQU. C.P.R. thanks to the Gobierno de Canarias for a fellowship.

References: [1] Alveranga, N., Ferro, E. A. (2005) In Studies in Natural Products Chemistry, Bioactive Natural Products. Elsevier Science. Amsterdam, 30: 635–702. [2] Cortés-Selva, F., Campillo, M. et al. (2004) J. Med. Chem. 77: 576–587.