Methyl eucomate

The crystal structure of the title compound [systematic name: methyl 3-carboxy-3-hydroxy-3-(4-hydroxybenzyl)propanoate], C12H14O6, is stabilized by intermolecular O—H⋯O and C—H⋯O hydrogen bonds. The molecules are arranged in layers, parallel to (001), which are interconnected by the O—H⋯O hydrogen bonds.

There is no heavy atom with a significant anomalous dispersion contribution, so the absolute configuration from the diffraction pattern itself could not be determined. However, the absolute configuration of the eucomic acid has been established by synthesis (Heller & Tamm, 1974) though its crystal structure has not been determined. Therefore the title compound is expected to share the same R configuration at the chiral centre C8.

Experimental
The title compound was purified from the stems of Opuntia vulgaris according to the reported procedures (Jiang et al., 2002).
Briefly, the stems of Opuntia vulgaris (1 kg) was extracted with 95% ethanol under room temperature. The extracted solution was concentrated with rotary evaporator to afford a crude extract, which was suspended in distilled water and partitioned with petroleum ether, ethyl acetate and n-butanol. Then the n-butanol fraction was subjected to silica gel column chromatography eluted with methanol-chloroform gradient solvent system to afford the title compound (16 mg). The transparent rectangular crystals of the title compound with average size of 0.50 × 0.40 × 0.30 mm were obtained by slow evaporation of the methanol solution at room temperature.

Refinement
Though all the hydrogens were discernible in the difference electron density maps. Neverheless, the hydrogens were situated into the idealized position and constrained during the refinement. Hydroxyl hydrogens: O-H equalled to 0.82 Å, U iso (H)=1.5 U eq O; C aryl -H equalled to 0.93 Å, U iso (H)=1.2 U eq C aryl ; C methylene -H equalled to 0.97 Å, U iso (H)=1.2 U eq C methylene ; C methyl -H equalled to 0.96 Å, U iso (H)=1.5 U eq C methyl .
There is no heavy atom with significant anomalous dispersion contribution in the structure for the used wavelength, so the absolute configuration from the diffraction pattern itself was not determined. 836 Friedel reflections were merged before supplementary materials sup-2 the refinement. However, the absolute configuration of the related eucomic acid has been established previously (Heller & Tamm, 1974) and therefore the title compound has been expected to share the same R configuration at the chiral center C8.
Reflection (0 0 2) was omitted. Fig. 1. The molecular structure of the title structure showing 30% probability displacement ellipsoids and the atom-numbering scheme.