3-Methyl-2-propionamidobutanoic acid

The reaction of propionyl isothiocyanate with valine was found to give the title compound, C8H15NO3, instead of the expected thiourea product. The whole molecule is non-planar and the carbonyl group is cis to the methylbutanoic acid group across the C—N bond. Intermolecular O—H⋯O and N—H⋯O hydrogen bonds build up a two-dimensional network developing parallel to (100).

The reaction of propionyl isothiocyanate with valine was found to give the title compound, C 8 H 15 NO 3 , instead of the expected thiourea product. The whole molecule is non-planar and the carbonyl group is cis to the methylbutanoic acid group across the C-N bond. Intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds build up a two-dimensional network developing parallel to (100).

Comment
The carbonoyl isothiocyanate is a well known intermediate for the synthesis of carbonoylthiourea deriatives. However, some carbonoyl isothiocyanates such as propionyl isothiocyanate was reactive enough to give N-propionylthiourea (Yamin & Othman,2008) after sitrring for about 1 h. In the present study, the reaction of propionyl isothiocyanate with valine did not give the expected thiourea derivative but instead the 3-methyl-2-propionamidobutanoic acid (I), thus indicating a nucleophilic substitution of the isothiocyanato group by the amino group of the amino acid.
The molecule adopts cis configuration with respect to the position of the 3-methylbutanoic acid group relative to the carbonyl O3 atom across the C3-N1 bond. The bond lengths and angles are within normal ranges (Allen et al., 1987). The

Refinement
H atoms attached to carbon atoms were positioned geometrically and treated as riding on their parent atoms with C-H= 0.96-0.98 Å and U iso (H)= xU eq (C) where x=1.5 for CH 3 group and 1.2 for CH 2 and CH groups. The hydrogen atoms attached to nitrogen and oxygen atoms were located from Fourier difference map and refined isotropically, Figures   Fig. 1. The nolecular structure of (I) with the atom-labeling scheme. Ellipsoids are drawn at the 30% probability level. H atoms are represented as small spheres of arbitrary radii. The enantiomer represented has S configuration.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(F 2 ) is used only for calculating Rfactors(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.