2-Azaniumyl-4-(ethylcarbamoyl)butanoate: the zwitterionic form of the amino acid theanine

In the title zwitterion, C7H14N2O3, the ethylamino and the 5-oxo groups are positionally disordered with occupancy ratios of 0.50:0.50 and 0.70:0.30, respectively. The terminal ethyl –CH3 group undergoes considerable thermal motion. In the crystal, molecules are linked via N—H⋯O hydrogen bonds, forming a two-dimensional arrangement propagating in the bc plane.

In the title zwitterion, C 7 H 14 N 2 O 3 , the ethylamino and the 5oxo groups are positionally disordered with occupancy ratios of 0.50:0.50 and 0.70:0.30, respectively. The terminal ethyl -CH 3 group undergoes considerable thermal motion. In the crystal, molecules are linked via N-HÁ Á ÁO hydrogen bonds, forming a two-dimensional arrangement propagating in the bc plane.

D-HÁ
In the crystal the molecules are linked via N-H···O hydrogen bonds to form a two-dimensional arrangement propagating in the bc-plane (Table 1, Fig. 2).

Experimental
The title compound was synthesized according to a Chinese Patent (Li, et al., 2006). 20 g of L-pyrrolidone carboxylic acid were reacted with 20 g of anhydrous ethylamine in helium gas under a pressure of 7 MPa for 4hr. 23.3 g of the theanine were obtained. The single crystals, of the title compound, suitable for X-ray diffraction analysis, were obtained by the hanging-drop method with water as solvent.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.