Identification of Tricyclic Guanidino Compounds from the Tetrodotoxin-Bearing Newt Taricha granulosa

Abstract

The biosynthesis of the potent neurotoxin tetrodotoxin (TTX, 1) is still unresolved. We used MS-guided screening and nuclear magnetic resonance analyses including long-range HSQMBC to characterize two novel skeletal tricyclic guanidino compounds, Tgr-288 (2a and 2b) and Tgr-210 (3), from the TTX-bearing newt, Taricha granulosa. The presence of these compounds in toxic newts is congruent with a previously proposed pathway for TTX biosynthesis in terrestrial organisms that includes a monoterpene precursor and the production of structurally diversified guanidino compounds.

Isolation and Biological Activity of 9-epiTetrodotoxin and Isolation of Tb-242B, Possible Biosynthetic Shunt Products of Tetrodotoxin from Pufferfish

“…However, 9- epi TTX ( 2 ) was also detected in newts. A different biosynthetic pathway toward TTX has been proposed in terrestrial organisms based on the structures of newt-specific cyclic guanidino compounds. − , Thus, a different route to produce 9- epi TTX ( 2 ) in terrestrial environments may exist, although this was not clear in the present study. We believe that these TTX and TTX-related compounds are all produced by microorganisms and then accumulated in pufferfish and other marine animals, as well as in newts.…”

“…Synthesis of Tb-series compounds including 5 was recently reported by Nishikawa’s group . Based on the structures of these compounds, a multistep oxidation process was predicted in the biosynthetic pathway toward TTX. , In terrestrial environments, a series of newt-specific 8- epi , and N -hydroxy analogues of TTX, 4,9-anhydro-10-hemiketal-5-deoxyTTX and bicyclic (Cep-210, Cep-212) , and tricyclic (Tgr-288, Tgr-210) guanidino compounds were isolated by our group, suggesting that TTX has a monoterpene origin. The structure of 4,9-anhydro-10-hemiketal-5-deoxyTTX was confirmed by recently reported total synthesis of an 8-deoxy analogue of this compound …”

A review of chemical defense in harlequin toads (Bufonidae: Atelopus)

“…HR-HILIC-LC/MS forms the basis of a mass spectrometry-guided screening method developed by Kudo et al (2014 , 2020) : it enables the detection of unknown compounds for subsequent structural analysis. The pattern of unique TTX analogs and other chemicals detected in newts via this method has led to the determination of a putative TTX biosynthetic pathway ( Kudo et al, 2014 , Kudo et al, 2016 , Kudo et al, 2020 , Kudo et al, 2021 , Kudo and Yotsu-Yamashita, 2019 ). Use of this screening method on Atelopus could help determine the extent of convergence in the biosynthetic pathway(s) of amphibian associated TTX.…”

Japanese Planocerid Flatworms: Difference in Composition of Tetrodotoxin and Its Analogs and the Effects of Ingestion by Toxin-Bearing Fishes in the Ryukyu Islands, Japan

“…In addition, non-toxic pufferfish can be produced by rearing them on TTX-free feed, and these non-toxic pufferfish rapidly toxify when fed TTX-containing feed, suggesting that TTX in wild pufferfish tissues is derived from prey organisms (Matsui et al 1981 , 1982 ; Honda et al 2005 ; Noguchi et al 2006 ; Itoi et al 2015 ). However, although the biosynthetic mechanism of TTX has been inferred from the discovery of various TTX analogs (Kudo et al 2014a , b , 2016 , 2020 , 2021 ; Ueyama et al 2018 ; Kudo and Yotsu-Yamashita 2019 ), there is no information on the gene cluster involved in this process.…”