On the conformational equilibrium of 16α-acetoxy-13, 1 7-seco-5α-androstan- 13ξ-hydroxy- 1 7-carboxylic acid lactone molecule in the crystalline state: X-ray study and MMX calculations

Gy Argay, A. K'a1mán, L. Párkányi, B. Ribár, Z. Ďjarmati

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Abstract

The reaction of l3,l7-seco-5α-androstan-13ξhydroxy.47carboxylic acid lactone with lead tetraacetate yields both α- and β-epimers. The structure of the α-epimer was determined by X-ray diffraction substantiating the ambiguous conclusions inferred from spectroscopic studies. Crystals are monoclinic, space group C2 with a= 28.003(3) Å, b= 7.351(2) Å, c = 18.970(4) Å, β = 90.75(2)°, Z8 (two molecules in the asymmetric unit) and Dc= 1.186 g cm-3. The structure determined by direct methods was refined toR= 0.049 for 2652 reflections. The conformational disorder of one of the symmetry independent molecules (A and B) was noticed at R=0.16. and corrected at the end of the standard refinement. The shape of the disordered δ-lactone ring in molecules B and B2 has been substantially improved by molecular mechanical calculations MMX. Altogether in the unit cell there are three conformers which differ in the puckering of the δ-lactone ring and the position of the 16α-acetoxy group. The predominant lactone ring conformation T/ S→S related by a C2 mode of rotation, is altered towards an envelope shape (E). The adjoining l6α-acetoxy group twice assumes pseudo-equatorial (conformerA (50%) and conformer B1, (25%) and once the pseudo-axial (conformer B2 (25%)) orientation.

Original languageEnglish
Pages (from-to)155-166
Number of pages12
JournalJournal of Molecular Structure
Volume248
Issue number1-2
DOIs
Publication statusPublished - Aug 1 1991

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy
  • Organic Chemistry
  • Inorganic Chemistry

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