The aim of the study was to isolate and elucidate structures of bioactive and/or new compounds from Indonesian medicinal plants. Following an ethnomedical investigation in Timor and Savu, twelve plants were selected for an initial brine shrimp assay. Extracts that showed cytotoxity in the brine shrimp assay were selected for further investigation using bioassay guided fractionation. The structures of isolated compounds were elucidated by mass spectrometry (MS) and nuclear magnetic resonance (NMR) techniques.
From the leaves of Pandanus amaryllifolius (Pandanaceae) collected in Jakarta, alkaloids having α-methyl-α,β-unsaturated-γ-lactone moieties were isolated. During this study, two different extraction methods, namely a solvent partitioning extraction and acid-base extraction, were tested, giving different types of alkaloids. A new secondary amine, 6E-pandanamine, was obtained from the solvent partitioning method. Acid-base extraction, on the other hand, afforded two new tertiary amines, pandanus-1 and pandanus-2. In addition to these, five known alkaloids were also isolated. Spectroscopic and chemical studies showed that the tertiary amines isolated from the acid-base extraction were artefacts formed during the extraction process. This finding suggests that the use of conventional acid-base treatment in isolating Pandanus alkaloids should be reviewed since it can introduce artefacts. Some of the alkaloids isolated showed nematocidal activities against the larval stages of Haemonchus contortus and Trichostrongylus colubriformis, two parasites living in sheep's intestines.
Extracts of the root of Ochrosia acuminata (Apocynaceae) have been used by people in Savu to treat tumour and ectopic pregnancy. Bioassay guided isolation using an in vitro antitumour assay led to the isolation of two antitumour alkaloids, ellipticine and 9-methoxyellipticine. Two new indole alkaloids, polyneuridine-N-oxide and 17-hydroxy-10-methoxyyohimbane, together with seven known alkaloids were also isolated. 17-Hydroxy- 10-methoxyyohimbane showed 100% inhibition against the larval development of both H. contortus and T. colubrifonnis at 100 μg/mL. The known compounds voachalotine, isoreserpiline, and quebrachidine showed moderate inhibition against H. contortus larvae, while reserpiline showed mild activity at 100 μg/mL.
In Timor, the bark of Alstonia scholaris (Apocynaceae) has been used to treat malaria. A new indole alkaloid, pseudoakuammiginone, and a new glycosidic indole alkaloid, echitamidine-N-oxide-19-Ο-β-D-glucopyranoside, together with five known alkaloids, were isolated from the trunk bark. The crude alkaloidal extract of the bark exhibits anti plasmodiaactivity with an IC50 value of 22.3 μg/mL against Plasmodium falciparum multi drug resistant strain Kl. All alkaloids isolated exhibited some antiplasmodial inhibition at the highest concentration tested (128 μg/mL). The known compounds Nb-demethylalstogustine and akuammicine were the most active compounds with IC50 values of 6.75 and 63.24 μg/mL respectively. In this study, some NMR assignments of the known compounds were revised based on our 2D NMR data.
Senna siamea (Fabaceae) is another plant that had been used in Timor to treat malaria. Antimalarial compounds from the leaf extract were isolated using bioassay guided isolation with an in vitro antiplasmodial assay. The polar extract caused 23% inhibition of the growth of P. falciparum at the highest concentration tested (128 μg/mL), while the non-polar extract showed an IC50 value of 24 μg/mL. The IC50 values of the non-polar extract did not increase with subsequent fractionation, which suggested that there were some synergistic effect of the components in the extract. Bioassay guided fractionation of the polar extract led to the isolation of a chromone, two flavonoids and some fatty acid components which showed activities in the antiplasmodial assay.