(E)-3-[2,5-Dioxo-3-(propan-2-ylidene)pyrrolidin-1-yl]acrylic acid

The title compound, C10H11NO4, was extracted from a culture broth of Penicillium verruculosum YL-52. The molecular structure is essentially planar, with an r.m.s. deviation of 0.01342 (2) Å for the non-H atoms. In the crystal structure, adjacent molecules are connected into a centrosymmetric dimer through a pair of O—H⋯O hydrogen bonds. The dimers are further extended into a chain by weak C—H⋯O hydrogen bonds.

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009  Comment Stellera chamaejasme L belongs to a toxic plant and its root has been used as Chinese traditional herb medicine in China. Our previous study resulted in isolating a fungal strain from the rhizosphere of Stellera Chamaejasme L identified as Penicillium verruculosum YL-52 (Yang et al., 2009). In this controbution, we reported the crystal structure of the title compound which was obtained from the culture broth of Penicillium verruculosum YL-52.
The bond lengths and angles of the title compound are within normal ranges (Cheng et al., 2009). In the crystal structure, the molecule, excluding methyl H atoms, is essentially planar, with an r.m.s. deviation of 0.01342 (2) Å. Moreover, adjacent two molecules are connected into a dimer through two head to head O1-H1···O2 hydrogen bonds. The dimers are further extended into a one-dimensional chain by weak C-H···O hydrogen bonds along the b axis, in which C6-H6A is donor and O4 is acceptor (Table 1 and Fig. 2).

Experimental
The roots of Stellera Chamaejasme L was collected in Qinling mountain of Taibai town in Shaanxi province, P. R. China, in August, 2007, and the fungal strain was isolated from the rhizosphere of the plant above, and deposited in our laboratory of natural product research, Northwest A&F University, Shaanxi Province, the People's Republic of China (culture collection number YL-52), and identified as Penicillium verruculosum YL-52. Repeated column chromatography of ethyl acetate extract of the culture broth of Penicillium verruculosum YL-52 provided the title compound.

Refinement
All H atoms were positioned geometrically and treated as riding, with C-H bond lengths constrained to 0.93 Å (CH), 0.97 Å (CH 2 ) and 0.96 Å (CH 3 ), and with U iso (H) = 1.2U eq (C) or 1.5U eq (methyl C). Fig. 1. View of the title molecular structure with atom numbering scheme and 30% probability displacement ellipsoids for non-hydrogen atoms.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O2