and zeylasteral (5) (Q105027438) (Figure D) . For the structural elucidation of isolated compounds, see "Material and Methods". The bioactivity of pristimerin and 11β-hydroxypristimerin was evaluated in vitro (zeylastral was not isolated in sufficient amounts for biological evaluation), and their activity was confirmed with IC 50 of 7.0 and 4.6 μM against L. donovani axenic amastigotes, for 3 and 4 respectively. Interestingly, 11β-hydroxypristimerin presented a higher selectivity index (14.0) on L. donovani axenic amastigotes than pristimerin (2.6), a compound reported as highly active against L.