Natural antamanide, a cyclic decapeptide from Amanita phalloides , has been shown to have the same conformation for the backbone and comparable side groups as the biologically active synthetic [Phe 4 , Val 6 ]antamanide. Packing in the crystal is quite different for the two compounds. Large channels with a polar lining are formed in the crystals of [Phe 4 , Val 6 ]antamanide, whereas in natural antamanide large channels in the crystal are completely surrounded by the lipophilic side groups of the Pro, Phe, and Ala residues. Antamanide, C 64 H 78 N 10 O 10 ·8H 2 O·X, crystallizes in space group P2 1 2 1 2 1 with a = 15.88 Å, b = 34.88 Å, and c = 13.61 Å.

Antamanide is the name we have given to a constituent of the fungus Amanita phalloides. This substance counteracts the lethal action of the Amanita toxins phalloidine and u-amanatine if administered to the white mouse before, or simultaneously with, the poisons. Its concentration in the fungus is, however, so low that the toxic action of the latter predominates. Antamanide is a cyclic decapeptide formed from the L-amino acids alanine, phenylalanine, proline, and valine in the molar ratio 1:4:4:f. The amino-acid sequence was determined by a combination of gas chromatography and mass spectrometry. The structural formula assigned was confirmed by synthesis according to a classic route of peptide chemistry.

On the Conformation and Synthesis of Diketopiperazines.

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