Shielding effect of ether CO bond obtained from proton chemical shifts of 4-oxa-5α- and 4-oxa-5β-androstan-17-ones

Abstract

4-Oxa-5α- and 4-oxa-5β-androstanones ( 1 and 2) were synthesized in order to obtain the NMR shielding parameters for the ether CO bond. The complete NMR assignment of both the proton and carbon atoms for these compounds and substituent-induced shifts (SIS) from the corresponding androstanones ( 3 and 4) are presented. The comparison of the molecular structure obtained by MM3 calculation with that of X-ray crystallographic analysis disclosed that the former structure is completely superimposable to the latter in both of the compounds 1 and 2. A combination of the electric field effect and the anisotropy of the magnetic susceptibility of the CO bond can successfully reproduced the observed SIS values for these androstanones.