1. Optimization of simultaneous analysis of tetrodotoxin, 4-epitetrodotoxin, 4,9-anhydrotetrodotoxin, and 5,6,11-trideoxytetrodotoxin by hydrophilic interaction liquid chromatography–tandem mass spectrometry
Mari Yotsu-Yamashita • Jun-Ho Jang • Yuko Cho • Keiichi Konoki. Forensic Toxicol (2011) 29:61–64
Tetrodotoxin (TTX) is one of the most important natural toxins being encountered especially in Japan. It is the primary toxin in puffer ﬁsh poisoning, acting as a powerful and speciﬁc voltage-gated sodium channel blocker. Many analogs of TTX, such as 4-epiTTX, 4,9-anhydroTTX, 11-norTTX-6(S)-ol, 11-norTTX-6(R)-ol, 5-deoxyTTX, 11-deoxyTTX, 6,11-dideoxyTTX, 5,6,11-trideoxyTTX, 4-cysteinylTTX, 11-oxoTTX, and tetrodonic acid have been found in puffer ﬁsh. Among them, 5,6,11-trideoxyTTX, 4-epiTTX, and 4,9-anhydroTTX, the latter two of which are chemically interchangeable with TTX, are the major analogs of TTX (Fig. 1). The LD50 (50% lethal dose, mice, intraperitoneal injection) of TTX was determined to be 10 lg/kg, and we previously reported that the dissociation constants (Ko) for the interactions of TTX, 4-epiTTX, 4,9-anhydroTTX, and 5,6,11-trideoxyTTX with the rat synapse membrane were 1.8, 68, 180, and [5000 nM, respectively.
2. Differential Effects of Tityus bahiensis Scorpion Venom on Tetrodotoxin-Sensitive and Tetrodotoxin-Resistant Sodium Currents
Eder R. Moraes • Evanguedes Kalapothakis • Lıgia A. Naves • Christopher Kushmerick. Neurotox Res (2011) 19:102–114
Mammalian sodium channels form a family of proteins with differential tissue distributions and pharmacological properties. Nine sodium channel pore-forming alpha subunits genes have been identiﬁed thus far, denominated NaV1.1–NaV1.9 (Catterall et al. 2003). The muscle isoforms, NaV1.4 and NaV1.5, are expressed in skeletal and cardiac myocytes, respectively. Splice variants of NaV1.5 are also expressed in the brain (Wang et al. 2009). The remaining isoforms are expressed predominantly in the central nervous system (NaV1.1, NaV1.2, NaV1.3, NaV1.6), peripheral nervous system (NaV1.7, NaV1.8), or both (NaV1.9). Sodium channels can also be classiﬁed based on their sensitivity to tetrodotoxin (TTX). Channels formed by NaV1.1, NaV1.2, NaV1.3, NaV1.4, NaV1.6, NaV1.7 alpha subunits are blocked by nanomolar concentrations of tetrodotoxin and are therefore considered TTX-sensitive (TTX-S). The remaining isoforms (NaV1.5, NaV1.8, NaV1.9) require micromolar tetrodotoxin for blockade and are therefore considered TTX-resistant (TTX-R).
3. Synthesis of crambescin B carboxylic acid, a potent inhibitor of voltage-gated sodium channels
Atsuo Nakazaki, Yuki Ishikawa, Yusuke Sawayama, Mari Yotsu-Yamashitab and Toshio Nishikawa*. Org. Biomol. Chem.,2014, 12,53–56
Considerable attention is currently devoted to the synthesis and properties of guanidine-containing natural products. Well-known examples of such compounds include tetrodotoxin and saxitoxin isolated as toxic principles of puﬀerfish intoxication and paralytic shellfish poison, respectively. These compounds exhibit potent blockage of sodium ion influx through voltage-gated sodium channels. Recently, we have focused on developing a subtype selective blocker of the sodium channels on the basis of natural products such as tetrodotoxin3 and saxitoxin. In this context, we were intrigued by the biological activities of carboxylic acid 2 of an alkaloid crambescin B isolated from the marine sponge Crambe crambe (Fig. 1), because of the similar zwitterion structure to tetrodotoxin; the spatial position of the guanidinium and carboxylate is similar to the guanidinium and orthoacid in tetrodotoxin (Fig. 2). Investigation of the biological activity of 2 has remained unexplored because crambescin B carboxylic acid 2 has not been isolated from natural sources and degradation of natural 1 into 2 has not been reported. Racemic synthesis of the twelve-carbon-chain homologue of carboxylic acid 2 has been reported by Snider et al.
4. Asymmetric synthesis of crambescin A–C carboxylic acids and their inhibitory activity on voltage-gated sodium channels
Atsuo Nakazaki, Yoshiki Nakane, Yuki Ishikawa, Mari Yotsu-Yamashitab and Toshio Nishikawa*. Org. Biomol. Chem.,2016, 14, 5304–5309
We investigated inhibitory activities on VGSCs of the six analogues, crambescin carboxylic acids 1a, 2 and 3 and crambescin B analogues 17, (+)-23 and (+)-24, by the cytotoxicity of ouabain and veratridine to mouse neuroblastoma cells (Neuro-2a), similar to the manner in which we previouslyestimated the activity of tetrodotoxin and its analogues (Table 1). Our previous studies demonstrated that racemic crambescin B carboxylic acid (±)-2 inhibited VGSCs with an EC50 value of 42 ± 25 nM, which was nine-fold larger than thatof tetrodotoxin (EC50 = 4.8 ± 2.6 nM). This study revealed that the natural dextro isomer was more potent than that of its enantiomer [(+)-2: 5.3 ± 2.2 nM vs. (−)-2: 79 ± 40 nM]. Moreover, this trend was also observed in all cases of crambescin A carboxylic acid 1a, crambescin C carboxylic acid 3 and decarboxylate 17; the EC50 for the natural dextro isomers was found to be more potent than those of each antipode.