Crystal structure of cis-2-(2-carb­oxy­cyclo­prop­yl)glycine (CCG-III) monohydrate

The title compound, C(6)H(9)NO(4)·H(2)O [systematic name: (αR,1R,2S)-rel-α-amino-2-carb­oxy­cyclo­propane­acetic acid monohydrate], crystallizes with two organic mol­ecules and two water mol­ecules in the asymmetric unit. The space group is P2(1) and the organic mol­ecules are enanti­omers, thus this is an example of a ‘false conglomerate’ with two mol­ecules of opposite handedness in the asymmetric unit (r.m.s. overlay fit = 0.056 Å for one mol­ecule and its inverted partner). Each mol­ecule exists as a zwitterion, with proton transfer from the amino acid carb­oxy­lic acid group to the amine group. In the crystal, the components are linked by N—H⋯O and O—H⋯O hydrogen bonds, generating (100) sheets. Conformationally restricted glutamate analogs are of inter­est due to their selective activation of different glutamate receptors, and the naturally occurring (+)-CCG-III is an inhibitor of glutamate uptake and the key geometrical parameters are discussed.