(2S,3R,4R,5R)-3,4-Dihydroxy-5-(hydroxymethyl)pyrrolidine-2-carboxylic acid [(2S,3R,4R,5R)-3,4-dihydroxy-5-(hydroxymethyl)proline]

The crystal structure of the title compound, C6H11NO5, establishes the relative configuration at the four stereogenic centres; the absolute configuration is determined by the use of d-glucuronolactone as the starting material for the synthesis. Molecules are linked by intermolecular O—H⋯O and N—H⋯O hydrogen bonds into a three-dimensional network, with each molecule acting as a donor and acceptor for five hydrogen bonds.

The crystal structure of the title compound, C 6 H 11 NO 5 , establishes the relative configuration at the four stereogenic centres; the absolute configuration is determined by the use of d-glucuronolactone as the starting material for the synthesis. Molecules are linked by intermolecular O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds into a three-dimensional network, with each molecule acting as a donor and acceptor for five hydrogen bonds.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH2896).

Comment
This paper firmly establishes the structure of the trihydroxyproline 1 (Fig. 1), the amino acid corresponding to DMDP 2.
The title compound (Fig. 2) was seen to adopt an envelope conformation with C4 out of the plane. The absolute configuration was determined by the use of D-glucuronolactone as the starting material for the synthesis. The molecule exists as an extensively hydrogen bonded nextwork with each molecule acting as a donor and acceptor for 5 hydrogen bonds (Fig.   3, Fig. 4). Only classical hydrogen bonding has been considered.

Experimental
The title compound was recrystallized from a mixture of hot ethanol and water: m.p. 449 K -decomposed; [α] D 25 +14.7 (c, 1.13 in H 2 O).

Refinement
Initial refinement of the Flack x parameter gave a value of -0.5 (10), suggesting that the absolute configuration could not be determined (Flack, 1983;Flack & Bernardinelli, 2000). Analysis of the Bijvoet differences using CRYSTALS gave the Hooft y parameter as -0.2 (7), and the probability the configuration is correct assuming the material is enantiopure was determioned to be 78.7% (Hooft et al., 2008;Thompson et al. 2008;Thompson & Watkin 2009). In the absence of significant anomalous scattering (FRIEDIF = 6.71; Flack & Shmueli, 2007), Friedel pairs were merged for the final refinement.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.