(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-hy-droxy-6-methyl-hept-5-en-2-yl]-2,6,6,10,11-penta-methyl-tetra-cyclo-[8.7.0.0(2,7).0(11,15)]hepta-decan-5-ol monohydrate}, C(30)H(52)O(2)·H(2)O, the three fused cyclo-hexane rings adopt chair conformations and the hy-droxy substituent of one of these occupies an axial position. The fused cyclo-pentane ring adopts an envelope conformation (with the flap atom being the C atom bearing the methyl group) and the 3-methyl-but-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 mol-ecules occupy special positions of 2 site symmetry. In the crystal, O(s)-H⋯O(w) and O(w)-H⋯O(s) (s = steroid and w = water) hydrogen bonds link hy-droxy groups and water mol-ecules, 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.