Alternariol

In the title compound (systematic name: 3,7,9-trihydroxy-1-methyl-6H-benzo[c]chromen-6-one), C14H10O5, the methyl group is shifted out of the molecular plane due to a steric collision, thus causing a slight twist of the benzene rings. The molecular structure is stabilized by an intramolecular O—H⋯O hydrogen bond, generating an S(6) ring. In the crystal, molecules are connected by intermolecular O—H⋯O hydrogen bonds into a three-dimensional network.

In the title compound (systematic name: 3,7,9-trihydroxy-1methyl-6H-benzo[c]chromen-6-one), C 14 H 10 O 5 , the methyl group is shifted out of the molecular plane due to a steric collision, thus causing a slight twist of the benzene rings. The molecular structure is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond, generating an S(6) ring. In the crystal, molecules are connected by intermolecular O-HÁ Á ÁO hydrogen bonds into a three-dimensional network.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: BT5266).

Comment
Alternariol is a cytotoxic, fetotoxic, teratogenic (Weidenbörner, 2001), mutagenic (Brugger et al., 2006, Wollenhaupt et al., 2008 and genotoxic (Fehr et al., 2009) mycotoxin produced by ubiquitous Alternaria fungi. It naturally occurs on fruits, vegetables and cereals like apples, tomatoes or wheat (Weidenbörner, 2001) and has also been obtained by total synthesis (Koch et al., 2005). The molecular structure of the title compound and the atom-labeling scheme are shown in Fig. 1. It is noteworthy that the benzene rings are not fully coplanar. This phenomenon is not observed for the benzo[c]chromen-6-one analogue 2-chloro-7-hydroxy-8-methyl-6H-benzo[c]chromen-6-one (Appel et al., 2006). Hence, the lacking planarity of the alternariol molecule may be attributed to a steric effect caused by the proximity of the H6A hydrogen to the C14 methyl group, which is not present in the planar analogue. This explanation is corroborated by the fact that the C8-C13-C14 angle is increased to 124.93 (17)°. The absolute configuration cannot be derived confidently since the molecule is a weak anomalous scatterer, which is documented by a large s.u. value for the Flack X parameter. Besides the intramolecular hydrogen bonds between O3-H3 and O2 (see dashed blue bonds in fig. 2), each molecule is connected to four adjacent molecules via intermolecular hydrogen bonds (see dashed green bonds in fig. 2). As a result undulated layers in the the ac plane are formed.

Experimental
Alternariol was supplied by the workgroup of Prof. R. Faust (University of Kassel, Germany) by total synthesis according to a literature procedure (Koch et al., 2005). Alternariol crystals were grown by sublimation in argon atmosphere. To do so, 100 mg of crude alternariol were heated to 380 °C for 2.5 h under a slow argon flow (atmospheric pressure). After cooling to room temperature, colourless needles could be collected from the water cooled compartment of the reaction vessel.

Refinement
In the absence of anomalous scatterers, the absolute structure cannot be determined therefore Friedel pairs were merged prior to refinement. The hydrogen atoms were located in difference maps and refined with U iso (H) set to 1.2 U eq of the parent atom (1.5 for methyl groups).

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.