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

Abstract

The ligand of the naturally occurring vanadium compound amavadin found in Amanita muscaria, (2 S, 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[(2 S,2′ S)- N-hydroxyimino-(2,2′)-dipropionate] 2 (=amavadin) changes from [ α ] D 25 = + 36 ° to + 114.0 ° ( c = 0.5, H 2O). For V[(2 R,2′ R)- N-hydroxyimino-(2,2′)-dipropionate] the optical rotation changes from [ α ] D 25 = - 36 ° to - 113.2 ° ( c = 0.5, H 2O).