Absolute configuration of methyl isoeichlerialactone

The title compound, C28H44O4·0.56H2O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component in a 0.55778 (3):0.44222 (3) ratio. The conformations of both components are identical except for that of the –COOCH3 group of the methyl propanoate side chain on the cyclohexane ring which is positionally disordered over two orientations. The molecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclohexane rings are in standard chair conformations and the cyclopentane ring adopts an envelope conformation. In the crystal, weak C—H⋯O interactions link methyl isoeichlerialactone molecules into screw chains along [010]. The crystal structure is further stabilized by O—H⋯O hydrogen bonds and weak C—H⋯O interactions.

The title compound, C 28 H 44 O 4 Á0.56H 2 O, is a co-crystal of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component in a 0.55778 (3):0.44222 (3) ratio. The conformations of both components are identical except for that of the -COOCH 3 group of the methyl propanoate side chain on the cyclohexane ring which is positionally disordered over two orientations. The molecule of methyl isoeichlerialactone has three fused rings and all rings are trans-fused. The two cyclohexane rings are in standard chair conformations and the cyclopentane ring adopts an envelope conformation. In the crystal, weak C-HÁ Á ÁO interactions link methyl isoeichlerialactone molecules into screw chains along [010]. The crystal structure is further stabilized by O-HÁ Á ÁO hydrogen bonds and weak C-HÁ Á ÁO interactions.
The asymmetric unit of the title compound ( Fig. 1) consists of methyl isoeichlerialactone monohydrate as the major component and methyl isoeichlerialactone as the minor component. The refined site-occupancy ratio of the major and minor components is 0.55778 (3)/0.44222 (3). The conformations and absolute configuration of both components are identical except for that of the COOCH 3 group of the methyl propanoate side chain (C1-C3/O1-O2/C28) on the cyclohexane ring is positionally disordered over two positions [A and B] with the occupancy ratio given above (Fig. 1). The molecule of methyl isoeichlerialactone, has three fused rings and all rings are trans-fused. The two cyclohexane rings are in standard chair conformations. The cyclopentane (C13-C17) adopts an envelope conformation with the puckered C14 atom having the maximum deviation of 0.259 (2) Å, Q = 0.420 (2) Å and θ = 202.9 (3)° whereas the furan ring (C20-C23/O3) is twisted with the twisted C20 and C21 atoms having the deviation of -0.144 (2) and 0.162 (3) Å, respectively from the C22/C23/O3 plane with Q = 0.259 (3) Å and θ = 64.2 (5)° (Cremer & Pople, 1975). Atoms C2, C3, C28, O1 and O2 of the methyl propanoate group are lie almost on the same plane with the r.m.s. deviation 0.0138 (2) and 0.0296 (2) Å for major and  (Allen et al., 1987) and comparable with the closely related compound (Fun et al., 2010).
The crystal packing of the major component is shown in Fig. 2, with the methyl isoeichlerialactone molecules being linked through weak C-H···O interactions (Table 1) (Table 1).
The seeds of Aglaia forbesii (48 g) were air-dried, ground, and exhaustively extracted with EtOH (3 x 500 mL) at room temperature. The combined extracts were concentrated under reduced pressure to afford a brown extract (5.7 g) which was resuspended in a mixture of MeOH and water and then extracted with n-hexane, CH 2 Cl 2 , and BuOH, successively.
The CH 2 Cl 2 fraction (1.87 g) was applied to column chromatography (CC) over silica gel (Merck, 0.063-0.200 mm) using gradient elution from 0% to 100% acetone in CH 2 Cl 2 , and finally washed down with MeOH. The fraction eluted with 20% acetone in CH 2 Cl 2 was further subjected to repeated silica gel column chromatography ((i) CC with Hexane/Acetone, 100:0 to 0:100 and (ii) CC with CH 2 Cl 2 /EtOAc, 98:2, v/v) to afford the title compound (3 mg). Colorless plate-shaped single crystals of the title compound suitable for X-ray structure determination were recrystallized from EtOH after several days. 1 H NMR and 13 C NMR spectral data  were consistent with the X-ray structure.

Refinement
All H atoms were placed in calculated positions with d(C-H) = 0.98 Å for CH; 0.97 Å for CH 2 and 0.96 Å for CH 3 atoms.
The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.99 Å from H25B and the deepest hole is located at 0.21 Å from C28B. 1634 Friedel pairs were used to determine the absolute configuration. Fig. 1. The molecular structure of the title compound, with 40% probability displacement ellipsoids and the atom-numbering scheme. Open bonds show the minor component.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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 > 2sigma(F 2 ) is used only for calculat-

sup-4
ing 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. (