Amavadin is a vanadium-containing coordination complex that occurs naturally. It is found found in three species of poisonous Amanita mushrooms: A. muscaria, A. regalis, and A. velatipes.
History and structure The ligand found in amavadin was first synthesized in 1954. Amavadin was first isolated and identified in 1972 by Kneifel and Bayer. In 1993, it was discovered by X-ray crystallography that amavadin is not a vanadyl ion complex. Instead, it is an octacoordinated vanadium(IV) complex. This vanadium center is bonded to two tetradentate ligands derived from N-hydroxyimino-2,2'-dipropionic acid, H3(HIDPA), ligands. The ligands coordinate through the nitrogen and the three oxygen centers.
The anionic complex is blue. It is an eight-coordinate vanadium complex. A Ca2+ cation is often used to crystallize amavadin to obtain a good quality X-ray diffraction. Oxidized amavadin can be isolated as its PPh4+ salt. The oxidized form contains vanadium(V), which has been studied by NMR spectroscopy.
Amavadin contains vanadium(IV). Initially, amavadin was thought to have a vanadyl, VO2+, center.
Amavadin is a C2-symmetric anion with a 3− charge. The twofold axis bisects the vanadium atom perpendicular to the two NO ligands. The anion features five chiral centers, one at vanadium and the four carbon atoms having S stereochemistry. There are two possible diastereomers for the ligands, (S,S)-(S,S)-Δ and (S,S)-(S,S)-Λ.
Preparation The formation of amavadin begins with the binding of two of the ligands. 2 HON(CH(CH3)CO2H)2 + VO2+ → [V{NO[CH(CH3)CO2]2}2]2− + H2O + 4 H+
Biological function The biological function of amavadin is unknown. It has been speculated that it uses H2O2 and acts as a peroxidase to aid the regeneration of damaged tissues. Amavadin may serve as a toxin for protection of the mushroom.
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