(20S)-Dammar-24-ene-3β,20-diol monohydrate from the bark of Aglaia exima (Meliaceae)

In the title compound {systematic name: (1R,2R,5R,7R,10R,11R,14S,15R)-14-[(2S)-2-hydroxy-6-methylhept-5-en-2-yl]-2,6,6,10,11-pentamethyltetracyclo[8.7.0.02,7.011,15]heptadecan-5-ol monohydrate}, C30H52O2·H2O, the three fused cyclohexane rings adopt chair conformations and the hydroxy substituent of one of these occupies an axial position. The fused cyclopentane ring adopts an envelope conformation (with the flap atom being the C atom bearing the methyl group) and the 3-methylbut-2-enyl portion of its substituent is disordered over three sets of sites in a 0.413 (7):0.250 (7):0.337 (7) ratio. The O atoms of both water molecules occupy special positions of 2 site symmetry. In the crystal, Os—H⋯Ow and Ow—H⋯Os (s = steroid and w = water) hydrogen bonds link hydroxy groups and water molecules, forming a three-dimensional network. The crystal studied was found to be a non-merohedral twin with a 0.518 (1):0.482 (1) component ratio.

The three cyclohexane rings that are fused together adopt chair conformations; the cyclopentane ring that is fused with a cyclohexane ring adopts an envelope conformation. The 3-methylbut-2-enyl portion of its substituent is disordered over three positions in an approximate 1:1:1 ratio. The O atoms of both water molecules lie on special positions of 2 site symmetry. Both hydroxy groups are hydrogen-bond donors to water molecules; the water molecules themselves are hydrogen-bond donors to hydroxy groups to generate a three-dimensional hydrogen-bonded network (Table 1).

Experimental
Aglaia exima was collected from the Bogor Botanical Garden, West Java, Indonesia in July 2006. The plant was identified by Herbarium Bogoriense of Bogor city. The dried and milled bark (3 kg) was extracted succesively by nhexane, ethyl acetate and methanol at room temperature. The ethyl acetate extract (300 g) was subjected to vacuum chromatography on silica gel G 60 by using a step gradient of n-hexane-ethyl acetate-methanol. The fraction eluted by nhexane/ethyl acetate (3:2) was further separated by column chromatography on silica gel (chloroform: methanol; 9.5:0.5) to give a colorless solid (63 mg). Colourless prisms were obtained by recrystallization from ethyl acetate solution. The chemical structure was established by NMR spectroscopic analysis; however, the analysis did not note the presence of water. The 3-methylbut-2-enyl chain is disordered over three sites in a 0.413 (7): 0.250: 0.337 ratio. The temperature factors of the singly-primed and doubly-primed atoms were set to those of the unprimed ones; the anisotropic temperature factors were restrained to be nearly isotropic. The 1,2-related distances were restrained to within 0.01 Å.

Carbon
The final difference Fourier map had a peak at 3.64 Å from H1c. The peak, which is close to a special position, could not be refined as a half oxygen atom.
The Flack parameter was calculated from 2574 Friedel pairs. The few oxygen atoms together with twinning and disorder precluded a more accurate refinement. The absolute configuration is that expected from spectroscopic assignments. Twinning and disorder probably contributed to the large weighting scheme.

Figure 1
The molecular structure of the title compound at the 70% probability level; hydrogen atoms are drawn as spheres of arbitrary radius. The disorder in the 3-methylbut-2-enyl chain is not shown.   (14) 0.0030 (8