In vitro Antiplasmodial Activity of 4-Phenylcoumarins from Exostema mexicanum

Abstract

The stem bark of Exostema mexicanum (Rubiaceae) is used in Latin American folk medicine as a quinine substitute for malaria treatment. Bioassay-guided fractionation of lipophilic and hydrophilic extracts from the stem bark and branches yielded two previously undescribed 4-phenylcoumarins: 4′,8-dihydroxy-5,7-dimethoxy-4-phenylcoumarin (exomexin A) and 3′,4′-dihydroxy-5,7,8-trimethoxy-4-phenylcoumarin (exomexin B). Together with five known derivatives the in vitro activities against a chloroquine-sensitive strain (poW) and a chloroquine-resistant strain (Dd2) of Plasmodium falciparum have been evaluated. The most lipophilic compound, 4′,5,7,8-tetramethoxy-4-phenylcoumarin (O-methylexostemin) revealed the strongest antiplasmodial activity (IC₅₀ values: 3.6 μg/ml [poW], 1.6 μg/ml [Dd2]).

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