Crystal Structure of Tetrahymanol Hemihydrate

The crystal structure of a hemihydrate of the pentacyclic triterpenoid tetrahymanol, C₃₀H₅₂O·1/2H₂O [monoclinic, P2₁, a = 7.417 (1) Å, b = 11.438 (2), c = 30.248 (4), β = 91.95°, Z = 4,R = 0.076] has been determined. Steric overcrowding warps the gross conformation of the two molecules in the asymmetric unit and generates unusually long carbon-carbon single bonds. The observed weakening of the C8–C14 bond, whose average length is 1.61 Å, is consistent with its scission observed in mass spectral experiments. Although the molecular skeleton possesses rotational symmetry, the observed conformations are markedly asymmetric, appear to be independent of the hydroxyl moiety, and suggest the presence of conformational isomers in solution.