Structures of N-hydroxy-type tetrodotoxin analogues and bicyclic guanidinium compounds found in toxic newts

Yuta Kudo, Charles T. Hanifin, Yuichi Kotaki, Mari Yotsu-Yamashita

Research output: Contribution to journalArticlepeer-review

18 Citations (Scopus)


The biosynthesis of tetrodotoxin (TTX, 1), a potent neurotoxin widely distributed in marine and terrestrial metazoans, remains unresolved. A significant issue has been identifying intermediates and shunt products associated with the biosynthetic pathway of TTX. We investigated TTX biosynthesis by screening and identifying new TTX-related compounds from Cynops ensicauda popei and Taricha granulosa. Mass spectrometry (MS)guided screening identified two new N-hydroxy TTX analogues in newts: 1-hydroxy-8-epiTTX (2) and 1-hydroxy-8-epi-5,11-dideox-yTTX (3, previously reported as 1-hydroxy-5,11-dideoxyTTX). We prepared a new analogue, 8-epi-5,11-dideoxyTTX (4), from 3 via N-OH reduction and confirmed the presence of 4 in T. granulosa using hydrophilic interaction liquid chromatography (HILIC)LCMS. The presence of 8-epi-type TTX analogues in both Cynops and Taricha supports a branched biosynthetic pathway of terrestrial TTX, which produces 6- and 8-epimers. In addition, new bicyclic guanidinium compounds Tgr-238 (5) and Tgr-240 (6) were identified as putative shunt products of our proposed TTX biosynthesis pathway. A structural analysis of Cep-228A (7), another bicyclic compound, was performed using NMR. Based on the structures of 5−7 and their analogues, we propose a model of the shunt and metabolic pathways of the terrestrial TTX biosynthesis.

Original languageEnglish
Pages (from-to)2706-2717
Number of pages12
JournalJournal of Natural Products
Issue number9
Publication statusPublished - 2020 Sept 25


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