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Antimalarial beta-carbolines from the New Zealand ascidian Pseudodistoma opacum
Journal
Journal of natural products
Volume
74
Number
9
Pages / Article-Number
1972-9
Abstract
One tetrahydro-beta-carboline, (-)-7-bromohomotrypargine (1), and three alkylguanidine-substituted beta-carbolines, opacalines A, B, and C (2-4), have been isolated from the New Zealand ascidian Pseudodistoma opacum. The structures of the metabolites were determined by analysis of mass spectrometric and 2D NMR spectroscopic data. Natural products 2 and 3, synthetic debromo analogues 8 and 9, and intermediate 16 exhibited moderate antimalarial activity toward a chloroquine-resistant strain of Plasmodium falciparum, with an IC(50) range of 2.5-14 muM. The biosynthesis of 1-4 is proposed to proceed via a Pictet-Spengler condensation of 6-bromotryptamine and the alpha-keto acid transamination product of either arginine or homoarginine. Cell separation and (1)H NMR analysis of P. opacum identified tetrahydro-beta-carboline 1 to be principally located in the zooids, while fully aromatized analogues 2-4 were localized to the test
