Steroidal analogues of unnatural configuration. Part 14. Conformational analysis of 4,4,14α-trimethyl-19(10→9β)abeo-5β,10α-pregnane-6,11-diols by X-ray crystallography and force-field calculations

Abstract

The X-ray structures of the 6α,11β-(6), 6β,11β-(7), and 6β,11α-diols (8) have been determined, and their conformations shown to be predicted accurately by the force-field method. The 6β,11α-diol (8) favours a flattener all-chair conformation, whereas rings B and C of (6) and (7) adopt non-chair conformations in response to served α-face interactions. The detailed conformational analysis of the 6,11-diols is discussed in terms of puckeinge parameters, and the steric energies of different conformers are compared. The 6α,11α-diol (9) for which X-ray crystallographic data could not be obtained is predicted by force-field calculations to prefer non-chair conformations of rings B and C, in apparent contradiction of spectroscopic findings.