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New 3,20-dihydroxy-13α-19-norpregna-1,3,5(10)-trienes were synthesized. The effects of these compounds on breast cancer cells and ERα activation were investigated. The scaffold of compounds containing the six-membered ring D′ annulated at 16α,17α-positions was constructed via the Lewis acid catalyzed Diels-Alder reaction of butadiene with 3-methoxy-13α-19-norpregna-1,3,5(10),16-tetraen-20-one 5 under a pressure of 600 MPa. The hydrogenation of primary cyclohexene adduct 6 followed by the one-pot reduction–demethylation (DIBAH) gave target epimeric 3,20-dihydroxy steroids 8a and 8b . The Corey-Chaykovsky reaction of the same conjugated ketone 5 gave a 16α,17α-methylene-substituted compound. The reaction of the latter with DIBAH yielded 3,20( R,S )-dihydroxy-16α,17α-methyleno-13α-19-norpregna-1,3,5(10)-triene 10 . The hydrogenation of the 16,17-double bond of compound 5 produced a mixture of 17α- and 17β-epimeric ketones, reduction–demethylation of which gave 3,20( S )-dihydroxy-13α,17α-19-norpregna-1,3,5(10)-triene 12a and 3,20( R )-dihydroxy-13α,17β-19-norpregna-1,3,5(10)-triene 12b . All compounds were fully characterized by 1D and 2D NMR, HRMS, and X-ray diffraction. All target compounds showed pronounced cytotoxic effect against MCF-7 breast cancer cells and NCI/ADR-RES doxorubicin-resistant cells at micromolar concentrations. The ER α -mediated luciferase reporter gene assay demonstrated that all compounds, except for compound 10 , are ER α inhibitors, while cyclopropane compound 10 proved to be an ER α activator. Docking experiments showed that all compounds are well accommodated to LBD ERα but have some differences in the binding mode. [ABSTRACT FROM AUTHOR]

New estrogen receptor α (ERα) antagonists – 3,20-dihydroxy-19-norpregna-1,3,5(10)-trienes containing an additional carbocyclic ring D′ at the 16α,17α positions – were synthesized. The effects of the new compounds on the MCF-7 breast cancer cells and ERα activation were investigated. All the steroids studied were synthesized starting from estrone methyl ether. The scaffold of compounds containing the six-membered ring D′ was constructed via the Diels–Alder reaction of butadiene with 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5 . The hydrogenation of primary 16α,17α-cyclohexeno-adduct 7 followed by 3-demethylation (by HBr–AcOH) and reduction of 20-oxo group (by LiAlH 4 ) or in one step by DIBAH gave target mono- and dihydroxy steroids 9 – 11 . The Corey–Chaykovsky reaction of the same 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5 gave 16α,17α-methylene-substituted compound. The reaction of the latter with DIBAH immediately yielded 3,20-dihydroxy-16α,17α-methyleno-19-norpregna-1,3,5(10)-triene 13 . The same procedures using 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5 produced corresponding 3,20-dihydroxy-16,17-19-norpregna-1,3,5(10)-triene 16 and 3,20-dihydroxy-19-norpregna-1,3,5(10),16-tetraene 17 . All compounds were fully characterized by 1D and 2D NMR, HRMS, and X-ray diffraction. The molecular docking showed that the target compounds can bind to ER, their binding mode being similar to that of natural estradiol. 16α,17α-Methylene- or unsubstituted compounds exhibit the highest cytotoxicity against MCF-7 cells, being simultaneously relatively weak ERα inhibitors. 3,20-Dihydroxy steroids containing the six-membered ring D′ proved to be the most effective ERα inhibitors. These compounds displayed moderate cytotoxicity comparable of that of tamoxifen and showed no toxic effect on MCF-10A normal, nontumorigenic epithelial cells. The new ER antagonists were found to be good candidates for further testing as agents for the treatment and prevention of ERα-positive breast cancers. [ABSTRACT FROM AUTHOR]