Novel Brominated Alkaloids from the Bryozoan Amathia citrina

Abstract

Sixteen bryozoan species from the United Kingdom and New Zealand were surveyed for the presence of brominated secondary metabolites by Liquid Chromatography tandem Mass Spectrometry (LCMS) analysis. Brominated metabolites were detected in six of these samples. Collections of the species Amathia citrina and Amathia verticillata were determined as ideal candidates for a natural products study due to the presence of potentially novel brominated secondary metabolites in reasonable abundance. The sample with the greatest number and seemingly highest concentration of brominated secondary metabolites, of all species surveyed, was the species Amathia citrina (previously Bowerbankia citrina) from Swansea, Wales, and so was selected as the candidate for this study. Eight related metabolites were detected in A. citrina, speculated to be a family of brominated alkaloids. Attempts were made to isolate and purify two members of this family of compounds by reversed-phase and size exclusion chromatography, but were unable to be obtained in a pure state. Nevertheless, they were then partially characterised by mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy to be discovered as a new family of brominated indole alkaloids, tentatively named the amathamines.