Xyloccensin E

The title compound (also known as phragmalin triacetate), C35H42O14, is a phragmalin-type limonoid extracted from X. rumphii. The molecule consists of eight rings with the orthoacetate group bridged at positions 1, 8 and 9. The two five-carbocyclic rings (A 1 and A 2) and the dioxolane ring (G) adopt a distorted envelope conformation. The 1,3-dioxane ring (E) exists in a chair conformation. The six-carbocyclic rings (B and C) exhibit a twisted-boat conformation. The lactone ring has a half-chair conformation and the furan ring is planar (r.m.s. deviation = 0.002 Å). Rings A 1/B, A 2/B, B/C, C/D and C/G are all cis-fused. The two acetoxy groups attached to ring B and the furan ring attached to the lactone ring are in equatorial positions. The porous crystal packing exhibits voids of 688 Å3 and weak intermolecular C—H⋯O interactions. The absolute configuration was assigned on the basis of literature data.

The title compound (also known as phragmalin triacetate), C 35 H 42 O 14 , is a phragmalin-type limonoid extracted from X. rumphii. The molecule consists of eight rings with the orthoacetate group bridged at positions 1, 8 and 9. The two five-carbocyclic rings (A 1 and A 2 ) and the dioxolane ring (G) adopt a distorted envelope conformation. The 1,3-dioxane ring (E) exists in a chair conformation. The six-carbocyclic rings (B and C) exhibit a twisted-boat conformation. The lactone ring has a half-chair conformation and the furan ring is planar (r.m.s. deviation = 0.002 Å ). Rings A 1 /B, A 2 /B, B/C, C/ D and C/G are all cis-fused. The two acetoxy groups attached to ring B and the furan ring attached to the lactone ring are in equatorial positions. The porous crystal packing exhibits voids of 688 Å 3 and weak intermolecular C-HÁ Á ÁO interactions. The absolute configuration was assigned on the basis of literature data.

Comment
Limonoid research from the Meliaceae family is of growing interest due to a range of biological activities, such as insect antifeedants and growth regulators, antibacterial, antifungal, antimalarial, anticancer and antiviral activities on humans (Koul et al., 2004). Such a focused interest upon limonoids from the Meliaceae family has already resulted in a discovery of several limonoids with novel skeletons, mostly, but not exclusively, from the genus Xylocarpus, and, in particular, the cannonball mangrove, Xylocarpus granatum Koenig (Cui et al., 2005;Pudhom et al., 2009). Limonoid derivatives have been found in all Xylocarpus plants studied, but their distribution and content may vary both between different plant species, and between parts or geocultivars of the same species. This, combined with their wide ranging structural diversity and potential biological significance across this plant family, prompted us to investigate another plant in this genus, Xylocarpus rumphii. Herein, the complete assignments of NMR data and the crystal and molecular structure of Xyloccensin E obtained from the seeds of X.
rumphii collected from Rayong Province, Thailand, in April 2009, were reported for the first time.

Experimental
Air-dried powdered seeds of X. rumphii (0.5 kg) were extracted with MeOH (2 L x 2, each for two days). The extract was concentrated under reduced pressure, followed by suspension in water and extraction with EtOAc. The resulting EtOAc crude extract (4.10 g) was chromatographed on a silica gel column eluted with a gradient of acetone-n-hexane (from 1:9 to 1:1) to yield 12 fractions. Fraction 12 (1.67 g) was further purified by silica gel column chromatography eluting with a gradient system of MeOH-CH 2 Cl 2 (from 2:98 to 5:95) and recrystallized from methanol to afford xyloccensin E (1, 79.0 mg).

Refinement
All H atoms were geometrically positioned and treated as riding atoms with distances C-H = 0.96 Å (CH 3 ), 0.97 Å (CH 2 ), 0.93 Å (CH), and Uiso(H) = 1.20 Ueq(C) for methylene and aromatic, 1.50 Ueq(C) for methyl. Hydrogen atoms bonded to C25 and C35 were treated as rotationally disordered between two orientations each in a ratio 1:1. The absolute structure could not be determined from the X-ray analysis, but it was known from earlier work on related compounds (e.g. Wu et al., 2004 andFan et al., 2007). 3652 Friedel pairs were therefore merged before the final refinement. The crystal structure contained solvent accessible voids of 688 Å 3 , showed no electrons in the voids. This might indicate that the crystal lost its solvent of crystallization without collapsing of the structure. The highest residual electron density peak (0.77 e Å -3 ) and the deepest hole (-0.27 e Å -3 ) were located 0.77 and 0.29 Å at O9 and C15, respectively. Fig. 1. The molecular structure of the title compound, showing the atomic numbering scheme and 30% probability displacement ellipsoids. Hydrogen atoms are omitted for clarity.