The Conformation of Cycloartenol Investigated by NMR and Molecular Mechanics

✍ Scribed by Alain Milon; Yoichi Nakatani; Jean-Pierre Kintzinger; Guy Ourisson

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: German
• Weight: 744 KB
• Volume: 72
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19890720102

✦ Synopsis

Cycloartenol(4), a natural plant sterol, was shown to be an effective membrane reinforcer; this was attributed to its conformation. We now present a conformational analysis of 4 by molecular modeling and NMR. Molecular modeling suggests that two conformations I and I1 coexist, differing mainly at the level of ring C, and of nearly equal energy, I and I1 each having ring A and B in a chair and half-chair conformation, respectively, with ring C 1,3-diplanar in I (solid-state structure as determined by X-ray crystallography) and in chair conformation in 11. A complete assignment of the 'Hand "C-NMR spectra of 4 and the entire coupling network in rings A and B is determined by various modem NMR techniques. The conformation of rings A and B thus determined is in agreement with conformations I and 11. Low-temperature NMR experiments show a fast equilibrium between two conformations, presumably I and 11. It is concluded, therefore, that the cyclopropane ring of 4 produces a flexibility at the level of ring C which may be important for the membrane properties.

') Steroid numbering system, according to the IUPAC-IUB rules [4]. We use the following abbreviations for the conformations of the 6-membered rings A X : chair (C), boat (B), and half-chair (H).