Rauvolfia dichotoma, a shrub of Apocynaceae, was collected from the Islands of SAO Tome and Principe and cultivated locally for medicinal purpose. Phytochemical investigation of 95% ethanol extract from the stems and leaves of R. dichotoma led to the isolation of two new Nb-oxide indole alkaloids, namely Nb-oxide-mitoridine (1) and Nb-oxide-raucaffricine (2), together with two known alkaloids (3-4) and eleven known lignans (5-15). Their chemical structures were elucidated by extensive NMR and HR-ESI-MS data analysis. All compounds (except 13) were tested for their β-hematin inhibitory activity. Compounds 2, 4, 14, and 15 showed certain inhibitory activity, indicating that they may have an antimalarial effect.
Keywords: Apocynaceae; Nb-oxide indole alkaloids; Rauvolfia dichotoma; antimalarial effect; β-hematin inhibitory activity.