Lacinilene C 7-methyl ether

The title compound, C16H20O3 [systematic name: 1-hydroxy-7-methoxy-1,6-dimethyl-4-(propan-2-yl)naphthalen-2(1H)-one], is a sesquiterpene isolated from foliar tissues of the cotton plant and is of interest with respect to its antibacterial properties. Its phenyl ring is ideally planar, and the maximum of deviation in the second ring is 0.386 (3) Å. The hydroxy group and the methyl group are oriented in an equatorial fashion and axial, respectively, to the second ring. In the crystal, inversion dimers are formed through pairs of O—H⋯O hydrogen bonds. Weak C—H⋯O hydrogen bonds link the dimers into columns along the c axis. These columns form a crystal structure with a crystal packing factor of 0.66.

The title compound, C 16 H 20 O 3 [systematic name: 1-hydroxy-7methoxy-1,6-dimethyl-4-(propan-2-yl)naphthalen-2(1H)one], is a sesquiterpene isolated from foliar tissues of the cotton plant and is of interest with respect to its antibacterial properties. Its phenyl ring is ideally planar, and the maximum of deviation in the second ring is 0.386 (3) Å . The hydroxy group and the methyl group are oriented in an equatorial fashion and axial, respectively, to the second ring. In the crystal, inversion dimers are formed through pairs of O-HÁ Á ÁO hydrogen bonds. Weak C-HÁ Á ÁO hydrogen bonds link the dimers into columns along the c axis. These columns form a crystal structure with a crystal packing factor of 0.66.

Comment
The title compound, C 16 H 20 O 3 , LCME is a sesquiterpene isolated from foliar tissues of the cotton plant. Its biosynthesis is induced in response to infection by the bacterial plant pathogen, Xanthomonas campestris pv. malvacearum; the latter is the causal agent of bacterial blight, and LCME exhibits antibacterial activity against this pathogen. LCME was originally isolated from Ulmus laciniata Mayr (Suzuki et al., 1972), but the proposed structure was incorrect. Subsequently, it was isolated together with lacinilene C from frost-killed cotton bracts (Gossypium species) and its structure was revised (Stipanovic et al., 1975). LCME is produced by autoxidation of 2-hydroxy-7-methoxycadalene, which also occurs in cotton plant foliage (Stipanovic et al., 1981). The biosynthesis was first elucidated by Essenberg et al. (1985). However, lacinilene C (the un-methylated derivative of lacinilene C 7-methyl ether) isolated from cotton tissues is optically active, which indicates it is the product of enzymatic transformation of 2,7-dihydroxycadalene (Essenberg et al., 1982). The conformation of the title molecule and numbering scheme of atoms is shown in Fig. 1. The atoms of the phenyl ring (C1-C4/C9/C10) are ideal planar with a r.m.s. = 0.0085 Å. In the second ring, the atoms C5-C7/C9/C10 lie in an ideal plane with a r.m.s. = 0.0313 Å, and the deviation from planarity of atom C8 is equal to 0.386 (3) Å. The dihedral angle between these planes is equal to 170.2 (1)°. The hydroxy group O3 and the methyl group C12 are oriented equatorially and axially to the second ring, respectively. In the crystal structure, the centrosymmetric dimers are formed through pairs of O3-H3···O2 i classical hydrogen bonds. Weak non-classical hydrogen bonds between C13-H13B···O2 ii of the centrosymmetric dimers associate into columns by translation along the c axis ( Fig. 2). Symmetry codes: (i) -x+1,-y+1,-z+2; (ii) x, y, z-1. The columns form a crystal structure with a packing factor 0.66.

Experimental
The title compound was isolated from frost-killed cotton bracts (Gossypium species) by extraction and silica gel LC procedures as previously described (Stipanovic et al., 1981). For achieving separation of the closely related compounds, the partially purified fraction was further chromatographed by consecutive injections on semi-preparative RP-HPLC column (Agilent 1100 HPLC system; Zorbax Eclipse XDB C8 column 9.4× 250 mm, 5µm; Agilent Technologies Inc, USA). The column was eluted using a linear gradient of H 2 O (A) /CH 3 OH (B) (HPLC grade, Sigma-Aldrich, DE) from 60 to 90% B for 30 minutes at a flow rate of 3 ml/min with the following segment of 100% B within 5 minutes and eluates were monitored at 254 nm. Crystals were obtained by slow evaporation of the HPLC eluent, and the most appropriate for X-ray diffraction were collected (m.p. 57-60°C).

Refinement
All H atoms were placed in geometrically idealized positions C-H = 0.98Å for methine H, C-H = 0.96Å for methyl H and C-H = 0.93Å for aromatic H and treated as riding on their parent atoms, with U iso (H) = 1.5U eq (C) for methyl H; U iso (H) = 1.2U eq (C) for aromatic and methine H. The H atom of hydroxy group was refined freely.

Figure 1
The molecular structure of title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms are presented as a small spheres of arbitrary radius.  Δρ min = −0.18 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.008 (2) Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'s 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 > 2σ(F 2 ) is used only for calculating R-factors(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 )