The first enantioselective synthesis of the amavadin ligand and its complexation to vanadium

The ligand of the naturally occurring vanadium compound amavadin found in Amanita muscaria, (2S, 2′S)-N-hydroxyimino-2,2′-dipropionic acid (1), was synthesized stereoselectively in two steps with 43% overall yield. After complexation of this ligand to vanadyl acetate, amavadin was isolated in quantitative yield. Due to the chirality at vanadium amavadin consists of a mixture of Δ and Λ diastereoisomers. Directly after its synthesis, the Δ to Λ ratio of amavadin is 2.27 and it decreases to 0.80 after equilibrium has been reached. During this epimerization the optical rotation for V[(2S,2′S)-N-hydroxyimino-(2,2′)-dipropionate]2 (=amavadin) changes from [α]D25=+36°to+114.0° (c = 0.5, H2O). For V[(2R,2′R)-N-hydroxyimino-(2,2′)-dipropionate] the optical rotation changes from [α]D25=-36°to-113.2° (c = 0.5, H2O).