The Alkaloid-Enriched Fraction of Pachysandra terminalis (Buxaceae) Shows Prominent Activity against Trypanosoma brucei rhodesiense

In the course of our studies on antiprotozoal natural products and following our recent discovery that certain aminosteroids and aminocycloartanoid compounds from Holarrhena africana A. DC. (Apocynaceae) and Buxus sempervirens L. (Buxaceae), respectively, are strong and selective antitrypanosomal agents, we have extended these studies to another plant, related to the latter—namely, Pachysandra terminalis Sieb. and Zucc. (Buxaceae). This species is known to contain aminosteroids similar to those of Holarrhena and structurally related to the aminocycloartanoids of Buxus. The dicholoromethane extract obtained from aerial parts of P. terminalis and, in particular, its alkaloid fraction obtained by acid–base partitioning showed prominent activity against Trypanosoma brucei rhodesiense (Tbr). Activity-guided fractionation along with extended UHPLC-(+)ESI QTOF MS analyses coupled with partial least squares (PLS) regression modelling relating the analytical profiles of various fractions with their bioactivity against Tbr highlighted eighteen constituents likely responsible for the antitrypanosomal activity. Detailed analysis of their (+)ESI mass spectral fragmentation allowed identification of four known constituents of P. terminalis as well as structural characterization of ten further amino-/amidosteroids not previously reported from this plant.