ABSTRACT
Continuing our search for herbicide models based on natural products, we investigated the action mechanisms of five alkaloids isolated from Swinglea glutinosa (Rutaceae): Citrusinine-I (1), glycocitrine-IV (2), 1,3,5-trihydroxy-10-methyl- 2,8-bis(3-methylbut-2-en-1-yl)-9(10H)-acridinone (3), (2R)-2-tert-butyl-3,10-dihydro-4,9-dihydroxy-11-methoxy-10-methylfuro[3,2-b]acridin-5(2H)-one (4), and (3R)-2,3,4,7-tetrahydro-3,5,8-trihydroxy-6-methoxy-2,2,7-trimethyl-12H-pyrano[2,3-a]acridin-12-one (5) on several photosynthetic activities in an attempt to find new compounds that affect photosynthesis. Through polarographic techniques, the compounds inhibited the non-cyclic electron transport in the basal, phosphorylating, and uncoupled conditions from H2 O to methylviologen (=MV). Therefore, they act as Hill reaction inhibitors. This approach still suggested that the compounds 4 and 5 had their interaction site located at photosystem I. Studies on fluorescence of chlorophyll a suggested that acridones (1-3) have different modes of interaction and inhibition sites on the photosystem II electron transport chain.
Subject(s)
Acridines/pharmacology , Alkaloids/pharmacology , Photosynthesis/drug effects , Photosystem I Protein Complex/antagonists & inhibitors , Photosystem II Protein Complex/antagonists & inhibitors , Rutaceae/chemistry , Acridines/chemistry , Acridines/isolation & purification , Acridones , Alkaloids/chemistry , Alkaloids/isolation & purification , Chlorophyll/chemistry , Chlorophyll/metabolism , Electron Transport/drug effects , Fluorescence , Photosystem I Protein Complex/chemistry , Photosystem I Protein Complex/metabolism , Photosystem II Protein Complex/chemistry , Photosystem II Protein Complex/metabolism , Structure-Activity RelationshipABSTRACT
OBJECTIVES: The known anti-protozoal activity of flavonoids has stimulated the testing of other derivatives from natural and synthetic sources. METHODS: As part of our efforts to find potential lead compounds, a number of flavonoids isolated from Neoraputia paraensis, N. magnifica, Murraya paniculata, (Rutaceae), Lonchocarpus montanus, L. latifolius, L. subglaucescens, L. atropurpureus, L. campestris, Deguelia hatschbachii (Leguminosae), dibenzoylmethanes from L. subglaucescens and synthetic analogues were tested for in-vitro activity against chloroquine-sensitive Plasmodium falciparum and Trypanosoma brucei rhodesiense bloodstream form trypomastigotes. An assay with KB cells has been developed in order to compare in-vitro cytotoxicity of flavonoids with a selective action on the parasites. KEY FINDINGS: Thirteen of the compounds tested had IC50 values ranging from 4.6 to 9.9 microm against T. brucei rhodesiense. In contrast, a small number of compounds showed significant activity against P. falciparum; seven of those tested had IC50 values ranging from 2.7 to 9.5 microm. Among the flavones only one had IC50 < 10 microm (7.6 microm), whereas against T. brucei rhodesiense seven had IC50 < 10 microm. Synthetic dibenzoylmethanes were the most active in terms of number (five) of compounds and the IC50 values (2.7-9.5 microm) against P. falciparum. CONCLUSIONS: Dibenzoylmethanes represent a novel class of compounds tested for the first time as antimalarial and trypanocidal agents.
