Structural elucidation and quantification of novel toxins in marine microalgae by NMR- and molecular modelling-based techniques

Abstract

Marine biotoxins produced by dinoflagellates exhibit a remarkable structural diversity. During the course of this thesis, I present the elucidation of six novel compounds in total, two for each of the toxin groups of azaspiracids, gymnodimines, and spirolides. The LC-MS based quantification, as used in shellfish surveillance, of the novel azaspiracids was compared with NMR based quantification. Further, four cyclic imine toxins had their full relative stereochemistry elucidated. The simulated chemical shifts revealed a systematic effect between the chirality at C 4 and neighboring nuclei. Based on this systematic effect, reasonable doubts arise towards determination of R configuration at C-4 in 13,19-didesmethyl SPX C. The configuration of C-4 was assigned with simulated and measured NMR spectra, suggesting that all tested GYMs and SPXs have the S configuration at that position. This assignment supports the hypothesis of a common biosynthetic pathway for both compound groups.