Search for new antiplasmodial leads in the oleo-gum-resin of Boswellia serrata Roxb.

Malaria is a vector-borne disease caused by pathogens of the genus Plasmodium that are transmitted by the bite of infected female Anopheles mosquitoes. Worldwide this infectious disease caused almost 430,000 deaths in 2015 [1]. Despite some improvements in prevention and therapy, especially increasing drug resistances remain a big problem [2]. As part of our continued search for natural products with antiprotozoal activity, Indian frankincense, the oleo-gum-resin of Boswellia serrata (Burseraceae) showed activity against Plasmodium falciparum (NF54 strain) in vitro. Successive extraction with solvents of increasing polarity showed best results for the dichloromethane extract (IC₅₀= 2.58 µg/ml). Bioactivity-guided fractionation led to the isolation of 22 compounds that were characterized by spectroscopic measurements. 17 compounds could be identified by comparison with literature data, three of which were obtained as natural products for the first time. The five remaining constituents were identified as rel-(1S,3R,7E,11S,12R)-1,12-epoxy-4-methylenecembr-7-ene-3,11-diol, 3-epi-neoilexonol, isoflindissol lactone, rel-(8R,9S,20R)-tirucall-24-ene-3β,20-diol and rel-(3α,8R,9S,20R,24S)-20,24-epoxytirucalla-3,25-diol. To the best of our knowledge, these compounds are not described in literature so far. All substances were tested for antiplasmodial activity in vitro using established protocols [3]. Isoflindissone lactone showed the best activity with an IC₅₀ value of 2.1 ± 0.3µM.

This project is an activity within the Research Network Natural Products against Neglected Diseases (ResNet NPND; http://www.resnetnpnd.org/). HLG thanks Cusanuswerk for a doctoral scholarship.

[1] WHO. Fact sheet: Malaria. Online: http://www.who.int/mediacentre/factsheets/fs094/en/; cited: March 20, 2017

[2] Schmidt TJ et al. Curr Med Chem 2012; 19: 2128 – 2175

[3] Nour AMM et al. Planta Med 2009; 75: 1363 – 1368