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Isomeric Tropane Alkaloids from the Aerial Parts of Schizanthus tricolor

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journal contribution
posted on 28.05.2010, 00:00 authored by Sylvian Cretton, Gaetan Glauser, Munir Humam, Damien Jeannerat, Orlando Muñoz, Louis Maes, Philippe Christen, Kurt Hostettmann
Investigation of the aerial parts of Schizanthus tricolor yielded seven isomeric tropane alkaloids: 3α-(1-methylitaconyl)-6β-senecioyloxytropane (1), 3α-(1-methylitaconyl)-6β-angeloyloxytropane (2), 3α-(1-methylmesaconyl)-6β-senecioyloxytropane (3), 3α-(1-methylmesaconyl)-6β-angeloyloxytropane (4), 3α-(1-methylmesaconyl)-6β-tigloyloxytropane (5), 3α-(1-methylcitraconyl)-6β-senecioyloxytropane (6), and 3α-(1-methylcitraconyl)-6β-angeloyloxytropane (7). Their structures were established by NMR including 1H, 13C NMR, HSQC, HMBC, COSY, and NOESY experiments, UV, IR, and mass spectrometry. Compounds 1, 6, and 7 are new to the literature. Alkaloids 1, 3, 4, and 5 and a mixture of 3, 4, and 5 were evaluated for in vitro antiplasmodial and cytotoxic activity. Compounds 1, 4, and 5 showed marginal inhibition of Plasmodium falciparum strain K1 with IC50 values of 22.8, 24.8, and 36.0 μM and displayed no cytotoxicity on MRC-65 cells (CC50 > 64 μM). Alkaloid 3 was inactive (IC50 63.5 μM). The alkaloid mixture exhibited slightly higher activity (IC50 17.0 μM) than the pure compounds, indicating some synergy between the different isomers.