(2R,4R)-1-(tert-Butoxycarbonyl)-4-methoxypyrrolidine-2-carboxylic acid

In the title compound, C11H19NO5, the five-membered pyrrolidine ring adopts an envelope conformation. The dihedral angles between the carboxyl group plane, the pyrrolidine ring and the methoxy group are 59.50 (3) and 62.02 (1)°, respectively. In the crystal, intermolecular O—H⋯O hydrogen bonds link the molecules into chains along [100]. The absolute configuration is assigned in accord with that of (2R,4R)-1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid, which was the starting material in the synthesis.

In the title compound, C 11 H 19 NO 5 , the five-membered pyrrolidine ring adopts an envelope conformation. The dihedral angles between the carboxyl group plane, the pyrrolidine ring and the methoxy group are 59.50 (3) and 62.02 (1) , respectively. In the crystal, intermolecular O-HÁ Á ÁO hydrogen bonds link the molecules into chains along [100]. The absolute configuration is assigned in accord with that of (2R,4R)-1-(tert-butoxycarbonyl)-4-hydroxypyrrolidine-2-carboxylic acid, which was the starting material in the synthesis.

Comment
Eribaxaban is a direct FXa inhibitors and has a high affinity for human FXa. Clinical data with eribaxaban in the prevention of VTE in TKR patients have recently been presented (Perzborn, 2009;Kohrt et al., 2007).
The pyrrolidine ring of the title compound adopts an envelope conformation with the C3 lying out of the plane. The dihedral angles between the carboxyl group plane, pyrrolidine ring and methoxy system are 120.50 (3)° and 117.98 (1)°, respectively. In the crystal structure, intermolecular O-H···O interactions contribute to the stabilization of the packing.
Each molecule is a donor and acceptor for 2 hydrogen bonds (TAble 1).
Experimental CH 3 I (22 g, 0.155 mol) and 60%(w/w)NaH (15 g, 0.625 mol) were dissolved in THF(300 ml), and the resulting mixture was cooled to 273 K in an ice bath. (R,R)-4-Hydroxy-pyrrolidine-1,2-dicarboxylic acid, 1-tert-butyl ester(35 g, 0.151 mol)was then added in portions while maintaining a reaction temperature of 278 K or less. The reaction was allowed to warm to 293 K overnight. To the reaction mixture was added H2O (100 ml), 1 N HCl(100 ml) and NaCl(42 g). The layers were separated, and the organic layer was dried over MgSO4, filtered and concentrated to the white solid (37 g). Colourless single crystals suitable for X-ray diffraction were obtained by recrystallisation from methanol.

Refinement
All H atoms were geometrically positioned (C-H 0.93-0.98 Å) and treated as riding, with U iso (H) = 1.2Ueq(C). Fig. 1. The structure of C 11 H 19 NO 5 with all non-H atom-labelling scheme and ellipsoids drawn at the 50% probability level.