Identification of Novel Gymnodimines and Spirolides from the Marine Dinoflagellate Alexandrium ostenfeldii

Abstract

Cyclic imine toxins are neurotoxic, macrocyclic compounds produced by marine dinoflagellates. Mass spectrometric screenings of extracts from natural plankton assemblages revealed a high chemical diversity among this toxin class, yet only few toxins are structurally known. Here we report the structural characterization of four novel cyclic-imine toxins (two gymnodimines (GYMs) and two spirolides (SPXs)) from cultures of Alexandrium ostenfeldii. A GYM with m/z 510 (1) was identified as 16-desmethylGYM D. A GYM with m/z 526 was identified as the hydroxylated degradation product of (1) with an exocyclic methylene at C-17 and an allylic hydroxyl group at C-18. This compound was named GYM E (2). We further identified a SPX with m/z 694 as 20-hydroxy-13,19-didesmethylSPX C (10) and a SPX with m/z 696 as 20-hydroxy-13,19-didesmethylSPX D (11). This is the first report of GYMs without a methyl group at ring D and SPXs with hydroxyl groups at position C-20. These compounds can be conceived as derivatives of the same nascent polyketide chain, supporting the hypothesis that GYMs and SPXs are produced through common biosynthetic genes. Both novel GYMs 1 and 2 were detected in significant amounts in extracts from natural plankton assemblages (1: 447 pg; 2: 1250 pg; 11: 40 pg per mL filtered seawater respectively).

Analysis of Cyclic Imines in Mussels (Mytilus galloprovincialis) from Galicia (NW Spain) by LC-MS/MS

“…The PtTX group has three elucidated structures with the same molecular weight, PtTX-A in addition to the epimers B and C [35]. The GYM group has five analogs named from A to E, with some methylated forms of GYM-A [30,33,36]. GYMs, SPXs, PnTXs, and PtTXs, which did not have available reference standard solutions, were monitored based on fragmentation pathways and references reviewed, combining different modes in mass spectrometry analysis.…”

Cyclic Imines (CIs) in Mussels from North-Central Adriatic Sea: First Evidence of Gymnodimine A in Italy

“…Shortly afterwards, two different GYM analogues (GYM B and GYM C) were discovered in the cell cultures of New Zealand K. selliformis [33,34]. Today, eight GYM analogues have been identified ( Figure 1) [28]. Besides the New Zealand episodes, GYMs have also been reported in many other countries (Table S1; Figure 2) [21,24,[35][36][37][38][39][40].…”

Mass Spectrometry-Based Characterization of New Spirolides from Alexandrium ostenfeldii (Dinophyceae)

“…This fragment is most likely formed by the protonation of the ether oxygen stabilized by the neighboring hydroxyl group and subsequent charge mediated fragmentation of the C11/12 bond (OH transfer from C10 to C12 and C11/12 cleavage [ 3 ]). Equivalent fragments were also observed for other SPX with a C10 hydroxyl group ( m/z 464, [ 11 ]). SPX G, which is isobaric with SPX 1 (same molecular mass), in contrast displays a different fragmentation pattern.…”

“…It is assumed to be the m/z 462 equivalent of SPX 1. In contrast to 5 , m/z 462 in SPX 1 [ 32 ] like in any other C-type spirolides [ 11 ] shows a very low relative abundance, which might be explained by differing configuration of the adjacent ring. This is additional confirmation of the hypothesis that 5 might be composed by a 6:5:6 ring configuration.…”

“…The first characterized SPX, which were gathered from Canadian microalgal and contaminated shellfish samples, included spirolides A-D and the 13-desmethyl analogue of SPX C (=SPX 1) [ 3 , 7 ] and D [ 8 ]. The 5:5:6 trispiroketal ring system spirolides were also observed from microalgal samples from the Adriatic coast [ 9 , 10 ] and as a structural feature of recently elucidated new spirolides from A. ostenfeldii strains from The Netherlands [ 11 ]. In addition, new spirolide subclasses, G-type [ 12 ] and SPX H/I [ 13 ] were discovered.…”