(−)-Dimethyl 3,3′-diphenyl-2,2′-[pyridine-2,6-diylbis(carbonylimino)]dipropanoate

The title compound, C27H27N3O6, a bis-amide derivative, is also a chiral amino acid ester with l-phenylalanine methyl ester groups as amine substituents. The pyridine ring is oriented at dihedral angles of 89.69 (3) and 62.95 (3)° with respect to the phenyl rings, while the dihedral angle between the phenyl rings is 60.76 (3)°. In the crystal structure, intermolecular N—H⋯O hydrogen bonds link the molecules into chains. One of the carbonyl O atoms and one of the methoxy CH3 groups are disordered over two positions. The O atom was refined with occupancies of 0.69 (13) and 0.31 (13), while C and H atoms were refined with occupancies of 0.69 (8) and 0.31 (8).

The title compound, C 27 H 27 N 3 O 6 , a bis-amide derivative, is also a chiral amino acid ester with l-phenylalanine methyl ester groups as amine substituents. The pyridine ring is oriented at dihedral angles of 89.69 (3) and 62.95 (3) with respect to the phenyl rings, while the dihedral angle between the phenyl rings is 60.76 (3) . In the crystal structure, intermolecular N-HÁ Á ÁO hydrogen bonds link the molecules into chains. One of the carbonyl O atoms and one of the methoxy CH 3 groups are disordered over two positions. The O atom was refined with occupancies of 0.69 (13) and 0.31 (13), while C and H atoms were refined with occupancies of 0.69 (8) and 0.31 (8).
In the structure of the title compound (Fig 1), the bond lengths (Allen et al., 1987) and angles are within normal ranges. with Amr et al. (1999) and according to the known S configuration at the C atom to which the benzyl group is attached. Both of C9 and C19 are chiral atoms in the structure. The pyridine-2,6-dicarboxamide core approximates C 2 point symmetry.
Such a feature seems to be common for symmetrically substituted pyridine-2,6-dicarboxamide derivatives.
In the crystal structure, intermolecular N-H···O hydrogen bonds (Table 1) link the molecules into chains, in which they may be effective in the stabilization of the structure.

Experimental
The title compound was synthesized by a slight modification of the literature method (Moriuchi et al., 2006). To a stirred mixture of L-phenylalanine methyl ester hydrochloride (129.4 mg, 0.6 mmol) in dry dichloromethane (15 ml) and triethylamine (0.21 ml, 1.5 mmol) was added dropwise 2,6-pyridyldicarbonyl dichloride (61.2 mg, 0.3 mmol) in dichloromethane (3 ml) at 273 K, and then stirred for 18 h at room temperature. The resulting mixture was diluted with dichloromethane, washed with saturated NaHCO 3 solution and brine, and then dried over anhydrous MgSO 4 . The solvent was evaporated in vacuo. The title compound was isolated as a colorless solid by recrystallization from ethanol (yield; 117.5 mg, 80%; m.p. 403-404 K, enantiomeric excess >99%). Crystals suitable for X-ray analysis were obtained from the mixed solution of

Refinement
The O4, C27, H27A, H27B and H27C atoms were disordered. During the refinement process, the disordered C and H atoms were refined with occupancies of 0.69 (8) and 0.31 (8), while O atom was refined with occupancies of 0.69 (13) and 0.31 (13). H atoms were positioned geometrically, with N-H = 0.86 Å (for NH) and C-H = 0.93, 0.98, 0.97 and 0.96 Å for aromatic, methine, methylene and methyl H, respectively, and constrained to ride on their parent atoms, with U iso (H) = xU eq (C,N), where x = 1.5 for methyl H and x = 1.2 for all other H atoms. In the absence of significant anomalous dispersion effects, Friedel pairs were averaged. Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme.