Composição química, atividade antiplasmódica in vitro e citotoxicidade de Geissospermum argenteum Woodson e G. urceolatum A. H. Gentry

Abstract

This work describes the chemical composition and in vitro antiplasmodial activity of extracts and compounds isolated from Geissospermum argenteum Woodson and G. urceolatum A. H. Gentry (Apocynaceae Jussieu). Bark, leaves and branches of both species were collected at the Reserva Florestal Adolpho Ducke, Manaus – AM. Through the experimental planning of simplex-centroid mixtures, extracts of bark, leaves and branches of G. argenteum were prepared with three components (acetone, methanol and water) for a chemometric study, in which the m/z data were obtained by electrospray ionization (ESI) mass spectrometry (MS) and were treated and interpreted using the Chemoface software. The same extracts were screened in two concentrations (5,0 and 50 µg/mL) for in vitro antiplasmodial activity against the K1 strain of Plasmodium falciparum and 50% inhibitory concentration (IC50) were determined at concentrations from 100 to 0, 13 µg/mL. The bark methanol extract was selected for fractionation, as it was the most active, as was the aqueous bark extract due to its medicinal relevance. Through maceration, 3% ammonium hydroxide methanol extracts were prepared from the bark of G. argenteum and G. urceolatum. The dry extracts were subjected to acid-base partitioning and the resulting alkaloid fractions that were fractionated using normal-phase, impregnated and RP-18 column chromatographies (CC). Preparative thin layer chromatography (PTLC) and high-performance liquid chromatography (HPLC) were also used to isolate the compounds. The identification of substances was performed by 1D and 2D nuclear magnetic resonance (NMR) and MS. Cytotoxicity was evaluated against the normal human fibroblast MRC-5 lineage using the alamar blue test. Three alkaloids from G. argenteum (GA) were isolated: flavopereirine, panarine, velosimine and four alkaloids from G. urceolatum (GU): aspidoscarpine, flavopereirine, geissolosimine and the new compound, 12- cinnamoyloxy-11-methoxyaspidospermidine, in addition to the triterpene lupeol. All G. argenteum bark extracts were active against P. falciparum (IC50 ₌ 0.20 to 10.0 µg/mL). The isolated alkaloids aspidocarpine, flavopereirine (GU/GA), geissolosimine, vellosimine and the new alkaloid were active against P. falciparum (IC50 ₌ 2.59, 1.25/2.55, 0.38, 3.59 and 0.48 µM, respectively). Among the active alkaloids above that were evaluated for cytotoxicity all presented satisfactory antiplasmodial: cytotoxicity selectivity indices (SI - 20-61).