Structural confirmation of ostreocin‐D by application of negative‐ion fast‐atom bombardment collision‐induced dissociation tandem mass spectrometric methods

Abstract

Negative-ion fast-atom bombardment collision-induced dissociation tandem mass spectrometric (FAB-CID-MS/MS) methodology was successfully applied to verify the highly complex structure of ostreocin-D (MW 2633), a new palytoxin analog isolated from the marine dinoflagellate Ostreopsis siamensis and proposed to be 42-hydroxy-3,26-didemethyl-19,44-dideoxypalytoxin based on NMR data. The charge-remote fragmentations were facilitated by a negative charge introduced to a terminal amino group or to a hydroxyl group at the other terminus by a reaction with 2-sulfobenzoic acid cyclic anhydride. Product ions generated from the [M - H](-) ions provided information on the structural details of ostreocin-D. Comparisons between the spectral data for ostreocin-D and palytoxin also provided a rational basis for the assignments of product ions.

High Resolution LC-MSn Fragmentation Pattern of Palytoxin as Template to Gain New Insights into Ovatoxin-a Structure. The Key Role of Calcium in MS Behavior of Palytoxins

“…Although the observed fragmentation was not as complete as that reported by Ukena et al [10] for the 2-sulfobenzoic acid derivative of ostreocin-D, the present approach required no derivatization. Therefore, HR LC-MS n spectra of palytoxin and ovatoxin-a could be used as fingerprints for a confident identification of these molecules in crude extracts.…”

“…Since natural extracts are usually contaminated by a complex mixture of palytoxin-like compounds (mascarenotoxins, ovatoxins, ostreocins, etc.) [10,17,18,21], this approach could also be used for a preliminary structural characterization of the unknown minor components contained in the extracts at levels too low for NMR studies.…”

“…The A-side fragment of cleavage #4 was also fragmented within MS 3 (precursor m/z 906.89327.1) and MS 4 (precursor m/z 906.8 9327.1 9309.1) experiments. The fragments obtained due to cleavages #1+#4, #2, and #3 (Table 2, Figure 1) provided information on the part structure ranging from C-8 to the A-side terminal of palytoxin which is a further region of the molecule where structural differences among palytoxin and most of its congeners (ostreocin-D, homo, bishomo-, neopalytoxin, ovatoxin-b, -c, and -e) occur [5,6,10,18]. Alternative fragmentation modes, namely pulsed Q collision induced dissociation (PQD) and high energy collision dissociation (HCD) were also investigated.…”

“…However, structural complexity of palytoxins is reflected in equally complex mass spectra, and this hampers a straightaway interpretation of their fragmentation patterns [9]. Significant efforts in this direction were made by Ukena et al [10], who used negative ion fast atom bombardment (FAB) collision induced dissociation (CID) tandem MS to confirm the structure of ostreocin-D. However, this study was not carried out on ostreocin-D itself but on a derivatized sample of ostreocin-D obtained by reaction with 2-sulfobenzoic acid cyclic anhydride; this resulted in introduction of a negative charge in the molecule that facilitated the charge-remote fragmentations.…”

Putative palytoxin and its new analogue, ovatoxin-a, in Ostreopsis ovata collected along the ligurian coasts during the 2006 toxic outbreak

“…Structure of ostreocin-D was assigned to 42-hydroxy-3,26-didemethyl-19,44-dideoxypalytoxin, based on NMR data [9,10], and verified by negative-ion fast-atom bombardment collision-induced dissociation tandem mass spectrometry [11]. The charge-remote fragmentations were facilitated by a negative charge introduced to the terminal amino group or to a hydroxyl group at the other terminus of the molecule by reaction of pure ostreocin-D with 2-sulfobenzoic acid cyclic anhydride.…”