14-Angeloyloxycacalohastine from Psacalium peltatum

The title compound [systematic name: (9-methoxy-3,5-dimethyl-5,6-dihydronaphtho[2,3-b]furan-4-yl)methyl 2-methylbut-2-enoate], C21H24O4, was isolated from matarique, or Psacalium peltatum (Kunth). The structure is almost planar. The angeloyloxy group makes an angle of 62.08 (2)° with the furanoeremophilane skeleton. The carbonyl O atom is disordered between two positions with a 76:24 ratio. The molecules in the crystal are joined by very weak C—H—O interactions in the ac plane.

NRV acknowledges a scholarship and financial support provided by the Conseja Nacional de Ciencia y Tecnología (CONACyT: 101038) and the Programa en Ciencias Biologicas of the Universidad Nacional Autó noma de Mé xico (UNAM).

Avilez Comment
The sesquiterpenes knows as eremophilanes contain in its basis skeleton a decalin system and most of them are found as furanoeremophilanes (Romo de Vivar et al., 2007). Psacalium peltatum (Kunth) Cass., is an endemic medicinal plant, a member of matarique complex, widely distributed in the central part of Mexico. The roots of P. peltatum have been shown biological activities (Alarcón-Aguilar et al., 2000;Bye et al., 1995;Contreras-Weber et al., 2002). Sesquiterpenes as cacalol and cacalone, isolated from P. decompositum, have been shown a clear inhibition of edema with a dose dependent in anti-inflammatory effect using in vivo models (Jimenez-Estrada et al., 2006). Even more, cacalone in a natural mixture with epi-cacalone reported the highest anti-inflammatory effect using in vivo 12-O-tetradecanoylphorbol-13-acetate (TPA) model (Acevedo-Quiroz, et al., 2008). Although the title compound has been isolated from several species of Senecio inaequidens, S. othonnae (Bohlmann et al., 1977) and S. canescens (Abdo et al., 1992), no report on the crystal structure determination of this compound has appeared. Therefore, due to this lack of data, the x-ray crystal structure determination of 14-angeloyloxycacalohastine was made.
14-Angeloyloxycacalohastine (I) has a furanoeremophilane skeleton (Fig. 1). Bond lengths and angles in (I) exhibit normal values (Allen et al., 1987). The structure is almost planar with C6 and C7 atoms out of the plane, forming a dihedral angle of 26.9 (1)° between central benzene ring and C4-C5-C6-C7 atoms. The angeloyloxy frame is almost perpendicular making a dihedral angle of 62.08 (2) to the furanoeremophilane skeleton. In absence of donor H atoms is noteworthy the fact that in the crystal structure, the molecules are linked by weak C-H···O intermolecular interaction (Table 1).
A voucher specimen was deposited at the National Herbarium (MEXU 1138692) of the Instituto of Biologia, UNAM, Mexico. Air-dried and powdered roots of P. peltatum were sequentially extracted with n-hexane by exhaustive maceration (3 × 2 l), at room temperature. Hexane extract of roots from P. peltatum, was separated in a chromatoghraphic column by elution with hexane -ethyl acetate in gradient mixture. 14-Angeloyloxycacalohastine was isolated from the fraction eluted by hexane.

Refinement
The positional parameters of H atoms were calculated geometrically (C-H = 0.93-0.98 Å). All H atoms were refined as riding with U iso (H) = 1.5U eq (C) for methyl H-atoms and U iso (H) = 1.2U eq (C) for other H-atoms. The carbonyl oxygen is disordered and has been refined in two positions. The ratio of SOF is 76/24 for O4/O4A respectively. In absence of heavy atoms the absolute configuration was not determined and the Friedel pairs were merged.

Figure 1
The structure of I with the numbering scheme. The thermal ellipsoids are drawn at 40% probability level. The disordered O4A atom was omitted for clarity.  where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.15 e Å −3 Δρ min = −0.15 e Å −3 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 > σ(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 )
x y z U iso */U eq Occ. (