Structural Analogues of Ibotenic Acid. Syntheses of 4-Methylhomoibotenic Acid and AMPA, Including the Crystal Structure of AMPA, Monohydrate.

Abstract
Ibotenic acid [(RS)-.alpha.-amino-3-hydroxyisoxazole-5-acetic acid], a structural analog of Glu isolated from Amanita muscaria, has a powerful excitatory effect on mammalian central neurones. (RS)-.alpha.-Amino-3-hydroxy-4-methylisoxazole-5-propionic acid (4-methylhomobiotenic acid) and (RS)-.alpha.-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) were prepared from 4,5-dimethyl-3-methoxyisoxazole. Crystals of the monohydrate of AMPA are triclinic, space group P.hivin.1 with cell dimensions a = 9.900(6), b = 7.152(3), c = 7.327(6) .ANG., .alpha. = 68.67(4), .beta. = 102.73(9), .gamma. = 101.77(5).degree.. The structure was solved by direct methods and refined by least-squares methods to a final R-value of 0.060. The 3-hydroxy-isoxazole moiety is unionized in the crystal structure.

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