Amanita phalloides ab initio calculation cyclopeptide hydrogen bond nonhuman protein structure stereochemistry structure analysis carbon nuclear magnetic resonance conference paper empiricism fungal protein molecular interaction protein conformation protein isolation structure activity relation toxic substance toxicity unclassified drug AM1 and ab initio studies Amanita virosa Heterocyclopeptides O-methyl-α-amanitin Phencyclopeptines Proline-rich Cyclic peptides S-deoxo-α-amanit in X ray crystallography alpha amanitin alpha amanitin sulfone alpha amanitin sulfoxide