Conformational flexibility in the molecular structure of rotenone, a naturally occurring insecticide

M. Rossi, P. Z. Fule, M. R. Taylor

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


The crystal and molecular structure of rotenone, a naturally occurring insecticide with mitochondrial and mitotic spindle inhibitory properties, was determined by direct methods. The crystals were orthorhombic, space group, P2I2I2I with two molecules in the asymmetric unit; a = 8.413 (1) A ̊, b = 19.840(1), c = 23.581(1), V = 3936 A ̊3, Z = 8. The structure was refined by least-squares methods to a final R = 0.067. The two molecules in the asymmetric unit have different conformations about the junction between the nonaromatic rings B and C. Ring B is in a sofa conformation in both molecules, with a slight distortion toward a half-chair in I, but with C8 and C8′ on opposite sides of the planar part of the rings. This difference in conformation results in I having an extended (linear) shape while II is V-shaped. The more elongated conformation of the molecule (I) has not been reported in previous studies. Ring C also has opposite conformations in the two molecules. The angle between the planes formed by rings A and D in molecule I is 64.3°, while in molecule II it is 88.3°. Molecular mechanics techniques were used to determine the energy of the two conformations. These calculations, at room temperature, predict molecule II to be the more stable conformer. The highly flexible site in the B/C ring junction is also chemically very reactive. This flexibility and reactivity are further discussed in terms of rotenone's inhibitory activities.

Original languageEnglish (US)
Pages (from-to)376-387
Number of pages12
JournalBioorganic Chemistry
Issue number4
StatePublished - Dec 1988

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Drug Discovery
  • Organic Chemistry


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