Crystal structure of limonoid TS3, isolated from Trichilia rubescens

The title limonoid compound, C26H28O5 center dot 0.5H(2)O (TS3) [systematic name: (3aS,3bS,4aS,5aS,6S,7aR,8aR,8bS,11aR)-6-(furan-3-yl)-3a,5a,8b,11a-tetramethyl-3a,4a,5,5a,6,7,7a,8b,11,11a-decahydrooxireno[2',3':4b,5]oxireno[2 '',3 '':2',3']cyclopenta[1',2':7,8]phenanthro[10,1-bc]furan-3(3aH)-one hemihydrate], crystallizes with two independent molecules (1 and 2) in the asymmetric unit and one water molecule. TS3 is composed of three six-membered rings (A, C and D), three five-membered rings (B, E and F) and two epoxide rings. A group of five fused rings (A-E) is bonded to a furan ring (F) with a Csp(3)-Csp(2) bond [1.500 (3) angstrom in molecule 1 and 1.499 (3) angstrom in molecule 2]. The absolute structures of the molecules in the crystal were determined by resonant scattering; Flack parameter = 0.05 (5). In the crystal, the individual molecules stack in columns along the b-axis direction. The water molecule bridges molecules 1 and 2 via O-water-H center dot center dot center dot O and C-H center dot center dot center dot O-water hydrogen bonds. Together with further C-H center dot center dot center dot O hydrogen bonds, linking molecules 1 and 2, the columns are linked to form slabs parallel to the ab plane. Within each column, molecules are also linked via C-H center dot center dot center dot pi interactions involving the five-membered furan (F) rings.