Ibotenic acid is a glutamate agonist found in Amanita muscaria mushrooms with chemical formula C5H6N2O4. Ibotenic acid breaks down into muscimol after dehydration and decarboxylation.

Chemical structure:

      H
       \
        O--C==O
           |
   H       C--H
    \     / \
     C===C   N--H
     |   |    \
     C   O     H
    /\\ /
H--O   N

Sources:
http://leda.lycaeum.org/Chemicals/Ibotenic_acid.145.shtml
http://www.erowid.org/plants/amanitas/references/journal/1979_mochtar_afghanistan1.shtml