Synthesis, binding affinities and uterotrophic activity of some 2-substituted estradiol and ring-A-fused pyrone derivatives

Efficient access to domain-integrated estradiol-flavone hybrids via the corresponding chalcones and their in vitro anticancer potential

Structural modification of the phenolic A-ring of estrogens at C-2 and/or C-3 significantly reduces or eliminates the hormonal effects of the compounds, thus the incorporation of other pharmacophores into these positions can provide biologically active derivatives suitable for new indications, without possessing unwanted side effects. As part of this work, A-ring integration of estradiol with chalcones and flavones was carried out in the hope of obtaining novel molecular hybrids with anticancer action. The syntheses were performed from 2-acetylestradiol-17β-acetate which was first reacted with various (hetero)aromatic aldehydes in a pyrrolidine-catalyzed reaction in DMSO. The chalcones thus obtained were then subjected to oxidative cyclization with I₂ in DMSO to afford estradiol-flavone hybrids in good yields. All newly synthesized derivatives were tested in vitro for cytotoxicity on human malignant cell lines of diverse origins as well as on a non-cancerous cell line, and the results demonstrated that estradiol-flavone hybrids containing a structure-integrated flavone moiety were the most active and cancer cell-selective agents. The minimal inhibitory concentration values (IC₅₀) were calculated for selected compounds (3c, 3d and 3e) and their apoptosis inducing capacity was verified by RT-qPCR (real-time quantitative polymerase chain reaction). The results suggest an important structure-activity relationship regarding estradiol-flavone hybrids that could form a promising synthetic platform and rationale for future drug developments.

Multistep Synthesis and In Vitro Anticancer Evaluation of 2-Pyrazolyl-Estradiol Derivatives, Pyrazolocoumarin-Estradiol Hybrids and Analogous Compounds

Although the hormone independent cytotoxic activity of several estradiol derivatives endowed with a simple substituent at C-2 has been reported so far, 2-heterocyclic and 2,3-condensed analogs are less investigated from both synthetic and pharmacological points of view. Therefore, novel A-ring-connected 2-pyrazoles of estradiol and, for comparison, their structurally simplified non-steroidal pairs were synthesized from estradiol 3-methyl ether and 6-methoxy-1,2,3,4-tetrahydronaphthalene. Friedel-Crafts acetylation of the protected phenolic compounds and subsequent O-demethylation led to ortho-substituted derivatives regioselectively, which were converted to arylhydrazones with phenylhydrazine, 4-tolylhydrazine and 4-chloro-phenylhydrazine, respectively, under microwave conditions. The hydrazones were subjected to cyclization with the Vilsmeier-Haack reagent immediately after preparation and the ring closure/formylation sequence resulted in steroidal and non-steroidal 4'-formylpyrazoles in moderate to good yields. During reductive transformations, 4-hydroxymethyl-pyrazoles were obtained, while oxidative lactonization of the 4-formylpyrazole moiety with the phenolic OH in the presence of the Jones reagent afforded A-ring-integrated pyrazolocoumarin hybrids and related analogs. Steroidal pyrazoles, which were produced as C-17 acetates due to acetylation of C-17 OH during the primary Friedel-Crafts reaction, underwent deacetylation in alkaline methanol to furnish 2-heterocyclic estradiol derivatives. Pharmacological studies revealed the overall and cancer cell-specific cytotoxicity of the derivatives and the half maximal inhibitory concentrations were obtained for the most promising compounds.

Synthesis, uterotrophic, and antiuterotrophic activities of some estradiol derivatives containing thiadiazole, thiazoline, and thiazolidinone moieties

The effect of structural modification on the biological activity of hormones has been studied on five novel series of estradiol analogs bearing a variety of substituents at the 2-position of the steroidal nucleus. The synthesized compounds include 2-[2-(5-substituted amino-1,3,4-thiadiazol-2-yl)vinyl]estradiol 17 beta-acetate 5-9, 2-aroylmethylestradiols 10-12, 2-[2-aryl-2-(substituted thiocarbamoylhydrazono)ethyl]estradiols 13-18 and their cyclic thiazoline 19-24, and thiazolidinone derivatives 25-30. Among the products, the p-hydroxybenzolmethylestradiol 12 exhibited the highest antiestrogenic activity of 63%. It also elicited 34% of the uterotrophic activity of estradiol.

Novel steroidal 1,4-diketones and pyridazine derivatives as potential antiestrogens

A series of steroidal 1,4-diketone derivatives was synthesized by acid-catalyzed condensation of 2-acetylestradiol-17 beta-acetate with substituted phenylglyoxals. Conversion of the products into the corresponding pyridazine derivatives was achieved by reaction with hydrazine hydrate. The synthesized compounds were evaluated for their uterotrophic, antiuterotrophic, and antifertility activities in mature female albino rats. Among the compounds tested, the phenyl 2, p-bromophenyl 3, and p-methoxyphenyl 5 diketone derivatives displayed uterotrophic activity of 72%, 72%, and 91%, respectively. The gradation of antiestrogenic activity was assessed in vivo by the inhibition of the estrone-stimulated uterine growth. Compounds 2-5 showed moderate antiestrogenic activity of 53-56%. None of the tested compounds elicited antifertility activity as assessed by the post-coital antiimplantation activity test.

2-(Hydroxyalkyl)estradiols: synthesis and biological evaluation

Synthetic estrogens possessing hydroxyalkyl side chains at the C-2 position of the A-ring were designed in order to further elucidate the structural and electronic requirements of the estrogen receptor to A-ring modifications. Furthermore, these compounds were envisaged as being stable analogs of the estradiol metabolite 2-hydroxyestradiol. The homologous series of 2-(hydroxyalkyl)estradiols 1-3 has been prepared by chain extension of 2-formylestradiol 6, which, in turn, was prepared via ortholithiation of estradiol. The substituted estradiols 1-3 were assayed for their abilities to bind to the estrogen receptor in MCF-7 cells and induce estrogen-responsive gene expression. The estradiol homologs exhibited significantly weaker affinity than estradiol for the MCF-7 cell estrogen receptor, with relative binding affinities (estradiol = 100) ranging from 1.11 for 2-(hydroxymethyl)estradiol (1) to 0.073 for 2-(hydroxypropyl)estradiol (3). The relative activities for mRNA induction of the pS2 gene by the estradiol homologs closely parallel the relative binding affinities for the estrogen receptor in MCF-7 cells. 2-(Hydroxymethyl)-estradiol exhibited similar estrogen receptor affinity and pS2 gene induction to the catechol estrogen 2-hydroxyestradiol and may prove useful in examination of the further biological effects of 2-hydroxyestrogen homologs.

4',17-dioxo-5'H-estra-1(10),4-dieno[3,2-b]furan: synthesis, binding affinity to the estrogen receptor, uterotrophic and antiimplantation activities

4',17-Dioxo-5'H-estra-1(10),4-dieno[3,2-b]furan (3) has been prepared by several routes starting from 2-bromoacetylestrone (2). Performance of the reaction with thiourea at elevated temperature provided compound 3 in good yield. When other reagents such as thiosemicarbazide, morpholine, sodium hydroxide or sodium hydride were treated with 2-bromoacetylestrone at room temperature, the furano derivative 3 was also obtained as the sole product. This new type of structural modification provided an estrogen nucleus deprived of the 3-hydroxyl function which was previously thought to be an essential requisite for binding to the estrogen receptor (ER). When evaluated in vitro for binding to the ER and in vivo for uterotrophic and antifertility activities, the furano derivative 3 was capable of inhibiting [3H]E2 binding by 16% while still eliciting high uterotrophic (99%) and postcoital antiimplantation (100%) activities relative to estradiol.