Xyloccensin L

The title compound, C32H40O10, also known as xyloccensin L [systematic name: (1R,4aR,4bS,5aR,6aR,9R,10S,10aS,10bR,2aR,13R)-1-(furan-3-yl)-6a-hydroxy-10-(2-methoxy-2-oxoethyl)-9,10a,12a-trimethyl-3-oxododecahydro-1H,3H,5aH-6,9-methanoisochromeno[6,5-f]oxireno[g]chromen-13-yl (2E)-2-methylbut-2-enoate], is a limonoid with a C1—C29 oxygen bridge: this is the first report of the X-ray crystal structure of such a limonoid. Two fused pyran rings and two cyclohexane rings adopt boat conformations, while another cyclohexane ring and the d-lactone ring are in half-chair conformations. The molecular structure is stabilized by intramolecular O—H⋯O hydrogen bonding.

The title compound (I), also known as xyloccensin L (Wu et al., 2004b), was previously isolated from seeds of a Chinese mangrove, X. granatum, which was collected from the Hainan island. As part of our research on bioactive compounds from mangrove plants of the Xylocarpus genus, we obtained the title compound again from seeds of an Indian mangrove, X. moluccensis, collected in the mangrove wetlands of Godavari estuary, Andhra Pradesh. The X-ray crystal structure analysis of (I) was undertaken in order to establish its relative stereochemistry and confirm our previously reported stereostructure (Wu et al., 2004b). Two fused pyran rings, C1/C2/C3/C4/C29/O10 and C1/C10/C5/C4/C29/O10, and two cyclohexane rings, C1/C2/C3/C4/C5/C10 and C8/C9/C11/C12/C13/C14, adopt boat conformations. However, the cyclohexane ring C1/

Experimental
Dried seeds (8.7 kg) of X. moluccensis were extracted three times with 95% EtOH at room temperature. The extract was concentrated under reduced pressure, followed by suspension in H 2 O and extraction with EtOAc. The resulting EtOAc extract (198.0 g) was chromatographed on silica gel eluted using a CHCl 3 -MeOH system (100:0 -5:1) to yield 127 fractions.

Refinement
All non-hydrogen atoms were refined anisotropically. All the H atoms were placed in geometrically idealized positions (C-H = 0.98 Å, with U iso (H) = 1.5U eq (C) for methyl groups; C-H = 0.99 Å, with U iso (H) = 1.2U eq (C) for methylene groups; C-H = 0.95 Å, with U iso (H) = 1.2U eq (C) for aromatic rings; C-H = 0.95 Å, with Uiso(H) = 1.2Ueq for alkyne supplementary materials sup-2 group, O-H = 0.84 Å, with U iso (H) = 1.5U eq (O) for hydroxyl group) and constrained to ride on their parent atoms. In the absence of significant anomalous scattering effects 2707 Friedel pairs have been merged. Fig. 1. The molecular structure of the title molecule, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. The intramolecular hydrogen bond is shown as a dashed line.

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 > 2sigma(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.