Conformations of Anaesthetic Steroids: a 1H and 13C NMR Study of (2β,3α,5α)-2-[(2R)-Ethyl-4- morpholinyl]-3-hydroxypregnane-11,20-dione and (2β,3α,5α)-2-[(2S)-Ethyl-4-morpholinyl]- 3-hydroxypregnane-11,20-dione.

✍ Scribed by Lee Fielding; Niall Hamilton; Ross McGuire

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 350 KB
• Volume: 35
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199703)35:3<184::aid-omr59>3.0.co;2-y

✦ Synopsis

The completely assigned 1H and 13C NMR spectra of the title diastereoisomers in solutions of and CDCl 3 are reported. NOE experiments show that these molecules adopt speciÐc conformations with no rota-DMSO-d 6 tion about the C-2ÈN bond in either solvent. In ring A of the steroid is in a twist-boat conformation and CDCl 3 , an intramolecular hydrogen bond from the 3a-OH to the morpholine N acts as a conformational lock preventing rotation of the morpholine ring. In solutions, ring A of the steroid is in a chair conformation and van der DMSO-d 6 Waals contacts with the 19-methyl group prevent free rotation of the morpholine ring. Molecular mechanics calculations produced four structures that account for the experimental data.