1-(5-Hydroxy-7-methoxy-2,2-dimethyl-2H-chromen-6-yl)ethan-1-one

The title chromene, C14H16O4, was isolated from the stems of Polyalthia plagioneura Diels. The molecular structure is stabilized by an intramolecular O–H⋯O hydrogen bond, which generates an S(6) ring. In the crystal, the molecules are linked by C—H⋯O interactions, generating [010] chains.


Comment
The title chromene was isolated from plants such as Remirea maritima (Allan et al., 1969), Euodia lunu-ankenda (Manandhar et al., 1985) and Evodia lepta (Li et al., 1997). In our ongoing studies of natural products with biological activity we isolated the chromene from the 75% EtOH extract of the stems of Polyalthia plagioneura, a plant used as a flok medicine which were collected from Bawangling, Hainan Province, P. R. China. We have undertaken the X-ray crystal structure analysis of the title compound in order to establish its molecular structure and relative stereochemistry.
The hydrogen bonds and angles are listed in Table 1.

Experimental
Air-dried stems of Polyalthia plagioneura (20 kg) were ground and percolated (4 × 3 h) with 75% EtOH at 60°C, which was suspended in 5 L water and then partitioned with chloroform, ethyl acetate and n-BuOH, successively, yielding a chloroform extract, an ethyl acetate extract and a n-BuOH extract, respectively. The chloroform extract was subjected to a silica gel CC column using petroleum ether as first eluent and then increasing the polarity with EtOAc, to afford 33 fractions. Fraction 5 was further separated by column chromatography with a gradient of chloroform-ether-EtOAc to give the title compound.
The crude product was recrystallised from ethyl acetate to yield colourless blocks of (I).

Refinement
H atoms bonded to C atoms were palced in geometrically calculated position and were refined using a riding model, with U iso (H) = 1.2 Ueq(C). H atoms attached to O atoms were found in a difference Fourier synthesis and were refined using a riding model, with the O-H distances fixed as initially found and with U iso (H) values set at 1.5 Ueq(O). Fig. 1. View of the title compound with displacement ellipsoids drawn at the 30% probability level.

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.