Structural Assignment of the Product Ion Generated from a Natural Ciguatoxin-3C Congener, 51-Hydroxyciguatoxin-3C, and Discovery of Distinguishable Signals in Congeners Bearing the 51-Hydroxy Group.

Ciguatoxins (CTXs) stand as the primary toxins causing ciguatera fish poisoning (CFP) and are essential compounds distinguished by their characteristic polycyclic ether structure. In a previous report, we identified the structures of product ions generated via homolytic fragmentation by assuming three charge sites in the mass spectrometry (MS)/MS spectrum of ciguatoxin-3C (CTX3C) using LC-MS. This study aims to elucidate the homolytic fragmentation of a ciguatoxin-3C congener. We assigned detailed structures of the product ions in the MS/MS spectrum of a naturally occurring ciguatoxin-3C congener, 51-hydroxyciguatoxin-3C (51-hydoxyCTX3C), employing liquid chromatography/quadrupole time-of-flight mass spectrometry with an atmospheric pressure chemical ionization (APCI) source. The introduction of a hydroxy substituent on C51 induced different fragmentation pathways, including a novel cleavage mechanism of the M ring involving the elimination of 51-OH and the formation of enol ether. Consequently, new cleavage patterns generated product ions at m / z 979 (C 55 H 79 O 15 ), 439 (C 24 H 39 O 7 ), 149 (C 10 H 13 O), 135 (C 9 H 11 O), and 115 (C 6 H 11 O 2 ). Additionally, characteristic product ions were observed at m / z 509 (C 28 H 45 O 8 ), 491 (C 28 H 43 O 7 ), 481 (C 26 H 41 O 8 ), 463 (C 26 H 39 O 7 ), 439 (C 24 H 39 O 7 ), 421 (C 24 H 37 O 6 ), 171 (C 9 H 15 O 3 ), 153 (C 9 H 13 O 2 ), 141 (C 8 H 13 O 2 ), and 123 (C 8 H 11 O).