Crystal structure of 3,4a,7,7,10a-pentamethyl-3-vinyldodecahydro-1H-benzo[f]chromen-9-ol isolated from Sideritis perfoliata

In the two independent molecules in the asymmetric unit of the title compound, the cyclohexane rings adopt a chair conformation, while the oxane rings are also puckered. In the crystal, O—H⋯ O hydrogen bonds connect adjacent molecules, forming a C(6) helical chain running along the [100] direction.


Chemical context
The Sideritis genus belonging to the Lamiaceae family is represented by more than 150 species in the world (Duman 2000). Sideritis species have been reported to have a broad spectrum of biological activities such as anti-inflammatory, anti-oxidant, anti-ulcerogenic, analgesic, antimicrobial, antiproliferative, anti-HIV and antifeedant activities (Gonzá lez-Burgos et al. 2011), and they have been consumed as teas, as flavoring agents, for therapeutic purposes, etc. In particular, Sideritis teas have been used for gastrointestinal disorders such as stomach ache and indigestion, to alleviate common colds, fever, flu and sore throats (Topçu et al. 2002). Phytochemical investigations of the species have revealed the presence of terpenes (Fraga et al. 2003), flavonoids, essential oils and other secondary metabolites (Barberan et al. 1985). As part of our studies in this area, we now describe the isolation and structure of the title compound, (I). ISSN 2056-9890

Supramolecular features
Intermolecular O-H. . . O hydrogen bonds connect adjacent molecules, forming C(6) helical chains located around a 2 1 screw axis running along the crystallographic a axis (Table 1 and Fig. 2). The crystal packing of these chains is governed only by van der Waals interactions. The two asymmetric molecules lead to pseudo-4 1 symmetry in space group P2 1 2 1 2 1 .

Theoretical calculations
PM3 (parameterized model number 3) is a semi-empirical method for the quantum calculation of the molecular electronic structure in computational chemistry. It is based on the neglect of differential diatomic overlap integral approximation. The semi-empirical PM3 parameterization used in the MOPAC program is widely used to derive charges, dipole moments and bond lengths. The computed quantum chemical descriptors include bond lengths, bond angles, torsion angles, atom charges, HOMO and LUMO energy levels, dipole moment, polarizability, etc. In the present case, the geometry of the molecule of the title compound was calculated with a semi-empirical PM3 method (Stewart, 1985). A spatial view is included in the Supporting information.
The calculated net charges at atoms O1 and O2 are À0.257 and À0.309 e À , respectively. The total energy and dipole moment of the title molecule are À3514.7 eV and 1.695 Debye. The HOMO and LUMO energy levels are À10.36 and 2.71 eV, respectively.
Calculated values for the geometrical parameter are consistent with those obtained by the X-ray structure determination, within the error limits (see Table S1 in the Supporting information), with the sole exception of the angles in the methoxy groups. This may be ascribed to the steric interactions between adjacent molecules in the crystal structure.

Figure 2
A view along the a axis of the crystal packing of the title compound. H atoms not involved in hydrogen bonding (dashed lines) have been omitted for clarity.
rotary evaporator, the extract was subjected to column chromatography (2.5 Â 70 cm); sephadex LH-20 (50 g) was used as a stationary phase and methanol was used as a mobile phase with a 0.25 ml min À1 flow rate. 16 fractions, each of which was 150 mL, were collected. Similar fractions were combined according to the TLC profile. Further purification was carried out with silica gel column chromatography to isolate the title compound. Colourless prisms were recrystallized from ethanol solution.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms bound to oxygen were found from difference Fourier maps and their positional parameters were refined with U iso fixed at 1.5 times U eq (O). H atoms bound to carbon were positioned geometrically and allowed to ride on their parent atoms with U iso = 1.2U eq (C) (C-H = 0.93 Å for aromatic, 0.97 Å for methylene and 0.98 Å for methine) and with U iso = 1.5U eq (C) (C-H = 0.96 Å ) for methyl H atoms. The absolute structure was indeterminate in the present experiment.
Acta Cryst. (2016). E72, 1380-1382 research communications   (Spek, 2009).  Special details Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell esds are taken into account in the estimation of distances, angles and torsion angles Refinement. Refinement on F 2 for ALL reflections except those flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating -R-factor-obs 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.