Determination of the absolute configuration of the nonsteroidal contraceptive agent centchroman by X-ray crystallography on its N-methyl iodide salt

X-ray crystallographic analysis of the N-methyl iodide salt of the d-enantiomer of the non-steroidal estrogen contraceptive agent centchroman (less active) indicates that the more active l-centchroman enantiomer has a 3R,4R configuration. This confirms a prediction made by us earlier and suggests that this ligand is bound to the estrogen receptor in a chroman/AB ring orientation relative to d-estradiol.