(S)-Methyl 2-benzamido-3-(3,4-dimethoxyphenyl)propanoate

The dimethoxypbenzene ring in the title compound, C19H21NO5, is gauche to the amide group and anti to the ester group. The chirality was confirmed to be S from two-dimensional NMR spectroscopy. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds and several short-contact interactions (2.07–3.45 Å) create chains parallel to [110]. The phenyl ring is disordered over two orientations in a 0.54 (2):0.46 (2) ratio.

The dimethoxypbenzene ring in the title compound, C 19 H 21 NO 5 , is gauche to the amide group and anti to the ester group. The chirality was confirmed to be S from twodimensional NMR spectroscopy. In the crystal, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds and several short-contact interactions (2.07-3.45 Å ) create chains parallel to [110]. The phenyl ring is disordered over two orientations in a 0.54 (2):0.46 (2) ratio.

Related literature
The title compound is a precusor to novel chiral organocatalyts. For the synthesis, see: Naicker et al.  Table 1 Hydrogen-bond geometry (Å , ).

Comment
The title compound is a well known precusor to several biologically active compounds (Zalán et al., 2006). In our laboratory it is being used as a precusor to novel chiral organocatalyts (Naicker et al. 2011).
There is only one analogous X-ray crystal structure that has a tertiary butyl group at the C12 position and a O-CH 2fluorenyl group is attached to the carbonyl carbon at C13 (Clegg & Elsegood, 2003). The title compound exists in a perfectly staggered conformation about the C9-C10 bond (Fig. 1). Similar to the analogous X-ray structure, the dimethoxyphenyl ring is gauche to the amide group and anti to the ester group.
The initial starting material for the synthesis of the title compound was optically pure L-DOPA, the chirality at the C8 atom remained unchanged during the synthesis and was confirmed to be S configuration from two-dimensional NMR spectroscopy.
The phenyl ring is disordered with two orientations at 50% site occupancy.
The reaction mixture was poured into 30 volumes of chilled water; the mixture was then extracted thrice with ethyl acetate (20 ml). The combined extracts were dried over anhydrous sodium sulfate and then concentrated to dryness affording the crude product. This crude product was purified by column chromatography (50:50 EtOAc/Hexane, Rf = 0.6) to afford the product 1.30 g (92%) as a white solid. Melting point: 377-379 K.
Recrystallization from ethyl acetate at room temperature afforded crystals suitable for X-ray analysis.

Refinement
All hydrogen atoms were positioned geometrically with C-H distances ranging from 0.95 Å to 1.00 Å and N-H distances 0.88Å and refined as riding on their parent atoms, with U iso (H) = 1.2 -1.5 U eq (C or N). The final refinements were done with the Friedel pairs being merged. The phenyl ring is disordered with two orientations: the ring of C14, C15A, C16A, C17A, C18A and C19A and the other ring of C14, C15B, C16B, C17B, C18B and C19B, with C17A and C17B are at the supplementary materials sup-2 common positions and the site occupancy factors were refined to 0.46 (2) and 0.54 (2) respectively. The bond distances of the disordered phenyl ring were restrained to 0.39 (1) Å. The hydrogen atom H1 (of N1) could not be located in the difference electron density maps and therefore was placed on a trigonal-planar position. This hydrogen position was justified by the presence of almost linear hydrogen bond N1-H1 to O5 of the neighbouring molecule. Fig. 1. The molecular structure of the title compound with the atom numbering scheme. Displacement ellipsoids are drawn at the 40% probability level.