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

4-Oxa-5 alpha- and 4-oxa-5 beta-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.