Tetrodonic acid-like substance; a possible precursor of tetrodotoxin

A tetrodonic acid-like substance which was hardly distinguishable from authentic tetrodonic acid in thin-layer chromatography, high performance liquid chromatography, etc., was successfully purified from the ribbon worm and flatworm by a method consisting mainly of Bio-Gel P-2 column chromatography. The tetrodonic acid-like substance showed a specific toxicity of approximately 700 mouse units/mg as tetrodotoxin, unlike tetrodonic acid which is a completely non-toxic substance. Instrumental analyses including gas chromatography-mass spectrometry, secondary ion mass spectrometry and thin-layer chromatography/fast atom bombardment mass spectrometry disclosed that the tetrodonic acid-like substance had a structure similar to, but not the same as, that of tetrodotoxin. This, along with its high convertibility into tetrodotoxin during storage and other experimental operations, suggested that the tetrodonic acid-like substance is a precursor of tetrodotoxin.