Chemical Characteristics of Synthetic LWTX4 and Paralytic Shellfish Toxins Under Standard Post–Column Oxidation (PCOX) and HILIC–MS/MS Conditions

The analytical characteristics of Lyngbya wollei toxin 4 (LWTX4), a rare derivative of saxitoxin (STX), remain insufficiently documented due to its limited availability. In the present study, therefore, LWTX4 was synthesized using the previously reported synthetic route developed by Looper to elucidate its fundamental chromatographic behavior. Additionally, three other paralytic shellfish toxin analogues, STX, decarbamoyl saxitoxin (dcSTX), and 12-epi-LWTX4, were prepared from a common intermediate. Analysis of synthetic LWTX4 using the AOAC OMA 2011.02 HPLC–PCOX–FLD method yielded a retention time of 19.8 min, which overlapped with that of STX, and revealed that its FLD response was one-fourteenth that of STX. Meanwhile, under the AOAC 2021 HILIC–MS/MS conditions, LWTX4 eluted at 7.29 min, producing major product ions at m/z 205.1204, 182.0926, 164.0822, and 110.0720. These chromatographic and mass spectrometric characteristics provide useful reference data for assessing the possible presence of LWTX4 during PST profiling of biological samples. The synthetic STX and dcSTX exhibited chromatographic behavior consistent with that of their corresponding certified reference materials (CRMs) under the standard HPLC–PCOX conditions, supporting the potential use of synthesis as a complementary approach to the isolation of PSTs from dinoflagellates for the preparation of CRMs.