Seco-oestradiols and some non-steroidal oestrogens: structural correlates of oestrogenic action

Abstract

Oestrogens can be grouped into two classes, based on their structural characteristics and biological activities; the typical oestrogens exemplified by the steroidal and the stilbene types, and the atypical oestrogens by the triaryl-ethylene types. In order to gain an understanding into the relationship between molecular structure and biological activity of oestrogens, receptor affinity, uterotrophic and antiimplantation activities of various 5,6-seco- and 9,11-seco-oestradiols, representing flexible analogues of the parent prototype, and certain 3-phenyl-4-aryl-chromenes and -chromans, representing triaryl-ethylene and -ethane prototypes incorporated into a rigid framework, have been studied.Comparative receptor affinity and biological activity of the seco-oestradiol analogues revealed the importance of the features of planarity and molecular rigidity of oestradiol-17ß for its high affinity to the receptor, and also led to a better appreciation of the characteristics of the receptor regions involved in binding around C-3, C-8, C-9 and C-18 of oestradiol. The results of the study on chromenes and chromans indicated that in triaryl-ethylene oestrogens, t-aminoalkoxy-phenyl residue plays an important role in receptor binding and biological activity. A study of the influence of alkyl groups at C-2 of the chromene and chroman analogues revealed noteworthy information about the general stereochemical requirements of these molecules for an optimum receptor fit. A consideration of these results and the findings previously reported in literature point to the possibility that all the molecular types considered here, interact with a common binding site of the receptor, albeit in a different stereochemical fashion, which may be one of the reasons for the differences in their biological activities.