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The methanolic extract from the leaves of the Vietnamese medicinal plant Maesa balansae showed potent in vitro and in vivo activity against the tropical protozoal parasite Leishmania infantum. Bioassay-guided purification of the extract led to the identification of six triterpenoid saponins, maesabalides I−VI (1−6), each having a strong and specific anti-leishmanial activity. Maesabalide III (3) and IV (4) were the most potent with IC50 values against intracellular amastigotes of about 7 and 14 ng/mL. In comparison, the IC50 value of sodium stibogluconate, the reference drug for treatment of leishmaniasis, is only 5.6 μg/mL. No cytotoxicity was present on a human fibroblast (MRC-5) cell line (CC50 > 32μg/mL). In vivo evaluation in the BALB/C mouse model demonstrated that >90% reduction of liver amastigote burdens was obtained 1 week after a single subcutaneous dose at 0.2−0.4 mg/kg was administered. Several chemical derivatives of maesabalides I−VI were prepared in order to study the structure−activity relationship.

Several quinone type compounds were isolated from the hexane, dichloromethane, and ethyl acetate extracts of the roots of Pentas longiflora. The hexane extract afforded two new compounds, [(3α,3‘α,4β,4‘β)-3,3‘]-dimethoxy-cis-[4,4‘-bis(3,4,5,10-tetrahydro-1H-naphtho[2,3-c]pyran)]-5,5‘,10,10‘-tetraone (1) and cis-3,4-dihydroxy-3,4-dihydromollugin (2), together with six known compounds, namely, pentalongin, mollugin, trans-3,4-dihydroxy-3,4-dihydromollugin, methyl-2,3-epoxy-3-prenyl-1,4-naphthoquinone-2-carboxylate, tectoquinone, and 3-hydroxymollugin. From the dichloromethane extract were isolated the three known compounds 3-methoxymollugin, methyl-3-prenyl-1,4-naphthoquinone-2-carboxylate, and scopoletin, while the ethyl acetate extract afforded the known 2-methoxy-3-methylanthraquinone.

A new homoprenylated benzochromene, methyl-5,10-dihydroxy-7-methoxy-3-methyl-3-[4-methyl-3-pentenyl]-3H-benzo[f]chromene-9-carboxylate (1), was isolated from the roots of Pentas bussei, collected from Kenya. The structure of this new compound was determined by spectroscopic data interpretation.

The bioassay-guided fractionation of a dichloromethane extract from the roots of Synaptolepis kirkii using neuronal viability as a model allowed the isolation of the new daphnane orthoester kirkinine (1a) as a powerful neurotrophic constituent.

A new type of tetracyclic naphthoquinone, named isagarin (1), was isolated from the hexane extract of the roots of Pentas longiflora. On the basis of spectral and X-ray diffraction analysis this compound was identified as 1,4-epoxy-4-methyl-1,2,4,5-tetrahydronaphtho[2.3-d]oxepin-6,11-dione.

The synthesis of the marine natural product laurencione from 5-hydroxy-2-pentanone in one step is reported.