N-(2-Carboxyethyl)-2,5-dideoxy-2,5-imino-d-mannonic acid [(3R,4R,5R)-1-(2-carboxyethyl)-3,4-dihydroxy-5-hydroxymethyl-l-proline]

The absolute stereochemistry of the title compound, C9H15NO7, was determined from the use of d-glucuronolactone as the starting material. The compound crystallizes as the zwitterion. The five-membered ring adopts an envelope conformation with the –CH2OH-substituted C atom forming the flap. An intramolecular N—H⋯O hydrogen-bond occurs. In the crystal, the compound exists as a three-dimensional O—H⋯O intermolecular hydrogen-bonded network with each molecule acting as a donor and acceptor for four hydrogen bonds.

The absolute stereochemistry of the title compound, C 9 H 15 NO 7 , was determined from the use of d-glucuronolactone as the starting material. The compound crystallizes as the zwitterion. The five-membered ring adopts an envelope conformation with the -CH 2 OH-substituted C atom forming the flap. An intramolecular N-HÁ Á ÁO hydrogen-bond occurs. In the crystal, the compound exists as a three-dimensional O-HÁ Á ÁO intermolecular hydrogen-bonded network with each molecule acting as a donor and acceptor for four hydrogen bonds.
Data collection: COLLECT (Nonius, 2001); cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO/SCALEPACK; program(s) used to solve structure: Superflip (Palatinus & Chapuis, 2007); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS. More than 250 iminosugars, sugar mimics in which the ring oxygen in a pyranose or furanose is replaced by nitrogen to form polyhydroxylated piperidines and pyrrolidines, have been isolated from plants (Asano et al., 2000;Watson et al., 2001). DMDP 1 (Fig. 1), originally isolated from Derris eliptica (Welter et al., 1976), but the most widely occurring iminosugar, is even found in potatoes . In contrast, BR1 2 from Baphia racemosa (Manning et al., 1985) and 7a-epialexaflorine 3 from Alexa grandiflora (Pereira et al., 1991) are among the very few corresponding sugar amino acids (SAA) found in nature. From examination of crude extracts of plants, it is clear that other SAA are natural products. As part of a program to make authentic samples of such SAA to identify them in crude plant extracts, the SAA corresponding to DMDP 4 (Best et al., 2010) was converted to the diacid 5 by initial reaction with tert-butyl acrylate in methanol in the presence of triethylamine followed by treatment with aqueous trifluoroacetic acid (Martínez, 2012). The structure of 5 was unequivocally determined by X-ray crystallographic analysis; the absolute configuration was determined by the use of d-glucuronolactone as the starting material for the synthesis.
The five ring adopts an envelope conformation with C5 out of the plane (Fig. 2). The compound exisits as a threedimensional O-H···O intermolecular hydrogen-bonded network with each molecule acting as a donor and acceptor for four hydrogen bonds (Fig. 3).

Experimental
The synthetic procedure is described in the comment section and illustrated in Fig. 1. The title compound was recrystallized from water: [α] D 25 -6.7 (c 0.75 in H 2 O); m.p. 523 K (decomposed).

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98, O-H = 0.82 Å) and Uĩso~(H) (in the range 1.2-1.5 times U~eq~ of the parent atom), after which the positions were refined with riding constraints (Cooper et al., 2010).