The structure of zetekitoxin AB, a saxitoxin analog from the Panamanian golden frog Atelopus zeteki : A potent sodium-channel blocker

doi:10.1073/pnas.0400368101

The structure of zetekitoxin AB, a saxitoxin analog from the Panamanian golden frog Atelopus zeteki: A potent sodium-channel blocker

^*Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan; ^‡Center for Molecular Design and Synthesis, Department of Chemistry, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea; ^§Department of Medicine, Emory University, Atlanta, GA 30322; ^¶Atlanta Veterans Affairs Medical Center, Decatur, GA 30033; ^∥Graduate School of Life Science, Tohoku University, Sendai 981-8555, Japan; and ^**Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892-0820

Contributed by John W. Daly, January 23, 2004

Abstract

Bufonid anurans of the genus Atelopus contain both steroidal bufadienolides and various guanidinium alkaloids of the tetrodotoxin class. The former inhibit sodium-potassium ATPases, whereas the latter block voltage-dependent sodium channels. The structure of one guanidinium alkaloid, zetekitoxin AB, has remained a mystery for over 30 years. The structure of this alkaloid now has been investigated with a sample of ≈0.3 mg, purified from extracts obtained decades ago from the Panamanian golden frog Atelopus zeteki. Detailed NMR and mass spectral analyses have provided the structure and relative stereochemistry of zetekitoxin AB and have revealed that it is an analog of saxitoxin. The proposed structure is characterized by richness of heteroatoms (C₁₆H₂₅N₈O₁₂S) and contains a unique 1,2-oxazolidine ring-fused lactam, a sulfate ester, and an N-hydroxycarbamate moiety. Zetekitoxin AB proved to be an extremely potent blocker of voltage-dependent sodium channels expressed in Xenopus oocytes. The IC₅₀ values were 280 pM for human heart channels, 6.1 pM for rat brain IIa channels, and 65 pM for rat skeletal muscle channels, thus being roughly 580-, 160-, and 63-fold more potent at these channels than saxitoxin.

Footnotes

↵ † To whom correspondence may be addressed: E-mail: myama{at}biochem.tohoku.ac.jp or kyh{at}kaist.ac.kr.
Abbreviations: CID, collision-induced dissociation; ESI, electrospray-ionization; TOF, time-of-flight; HMBC, heteronuclear multiple-bond correlations; NOE, nuclear Overhauser effect.