Larrea tridentata—Absolute configuration of its epoxylignans and investigations on its antiprotozoal activity

Abstract

The dichloromethane extract of Larrea tridentata (Creosote bush, Zygophyllaceae) showed activity against the protozoan pathogens Trypanosoma brucei rhodesiense, Trypanosoma cruzi, Leishmania donovani and Plasmodium falciparum (IC50 2.8, 14.6, 5.2, 2.9μg/ml, cytotoxicity against L6 rat skeletal myoblasts: 25.4μg/ml).In search for potentially active constituents, nine lignans (three dibenzylbutanes, four epoxylignans, two aryltetralins), six flavonoids and one ester of ferulic acid (3′-oxohexylferulate) were isolated and identified by spectroscopic methods.Since some ambiguities with respect to the absolute configuration of several chiral lignans from L. tridentata were found in the literature, CD spectra were recorded and correlated with results from quantum mechanical spectra simulations (TD-DFT at the B3LYP/6-31D(d,p) level). Thereby, the absolute stereochemistry of these lignans can now be assigned with certainty.The activity of the isolated constituents against the protozoan parasites was investigated. The major lignan meso-nordihydroguaiaretic acid (NDGA), mainly responsible for the anti-inflammatory effects of this plant, was found to be the most active compound (IC50 values: 4.5, 33.1, 12.0 and 7.7μM against the mentioned parasites, respectively, 33.1μM for cytotoxicity against L6 rat skeletal myoblasts). Although its level of activity is only moderate, NDGA can thus also be considered the main active compound for the antiprotozoal activity of L. tridentata.