Components of the Green Deathcap Toadstool (Amanita phalloides ), LIX. The Spatial Structure of Phallotoxins

The thioether bridge (CH sub(2) - S -C( alpha -indole)) in the phallotoxin molecule is an inherently dissymmetric chromophore responsible for the positive Cotton effects centered around 290 nm in CD spectra. The helicity of this structural element, M- or P-, could not be recognized unambigously by super(1)H-NMR analysis previously performed. A less complex cyclic thioether peptide, 2-mercapto-L-tryptophylglycylcysteine cyclic (1 arrow right 3) sulfide exhibits a CD spectrum showing the Cotton effects around 290 nm nearly exactly in a negative sense as mirror image of those of the phallotoxins. The structural analysis by 360 MHz super(1)H-NMR suggested M-helicity of the chromophore. Unquestionable proof was obtained by X-ray structure analysis of the N-p-bromobenzenesulfonyl derivative resulting in a M-helical thioether moiety. Therefore to the phallotoxins with analogous but positive Cotton effects around 290 nm a P-helical thioether structure must be ascribed.