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Fenestranes are regarded as a particularly challenging synthetic targets, and only few syntheses have been reported in the recent past. These rare compounds of synthetic and theoretical interest are a class of tetracyclic skeletons, defined as doubly a,a'-bridged spiroalkanes. The reported results are focused on the synthesis of new and original [4.6.4.6]fenestradienes 3a-f and [4.6.4.6]fenestrenes 4a-e. Our approach implies the formation of this tetracyclic structure by a reaction cascade, based on consecutive transformations starting from the trienyne 1a-f: an initial soft hydrogenation using a P-2 Nickel catalyst at room temperature, followed by a conrotatory 8p electrocyclization and a disrotatory 6p electrocyclization and a final oxidation. Several examples of this type of new compounds are described in this Communication.

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Diethylstilbestrol (DES) and hexestrol (HES) are carcinogenic synthetic estrogens. The major metabolites of these compounds are their catechol derivatives, 3'-OH-DES and 3'-OH-HES. Oxidation of these metabolites leads to the electrophilic quinones, which are presumably involved in the tumor-initiating process. A synthetic route based on the McMurry coupling reaction was developed for the synthesis of 3'-OH-DES. Using commercially inexpensive starting materials, this compound was synthesized in four steps, and the cis and trans isomers were separated and identified. Following the same synthetic route, 3'-OH-HES was synthesized in five steps.

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3-Azibutyl (2R*,3S*)-2,3-bis(4-hydroxyphenyl)pentyl sulfide (1), a photoaffinity labeling reagent for the estrogen receptor (ER), has been prepared in unlabeled and in high specific activity tritium-labeled form (32 Ci/mmol) and has been shown to undergo selective and efficient photocovalent attachment to rat uterine ER. Diazirine 1 demonstrates high binding affinity for ER, as determined by both a competitive binding assay and a direct binding assay (relative binding: estradiol = 100; (1) = 17. Kd: estradiol = 0.19 nM; (1) = 0.98 nM, respectively). It is efficient in site-specific photoinactivation of ER, reaching the level of 31% after 5 min of irradiation at > 315 nm. The tritium-labeled diazirine [3H]-1 undergoes specific photocovalent attachment to ER with an attachment efficiency of 29% and a selectivity of 90%. Both of these values are quite high for a photoaffinity reagent. SDS-polyacrylamide gel electrophoretic analysis of the photolabeled proteins shows specific labeling of a major species at M(r) 65,000, the same species that is labeled by [3H]tamoxifen aziridine, a well-characterized affinity label for ER. Hexestrol diazirine 1 is the first carbene-generating photoaffinity label that covalently labels ER with high efficiency and selectivity, and it should be useful in further studies on the hormone-binding domain of ER.

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We have prepared two non-steroidal estrogens in the 2-oxohexestrol series labeled with the positron-emitting radionuclide fluorine-18, 1-fluoro-5-oxohexestrol (4) and 1-fluoro-2-oxohexesterol (5). We anticipated that the polar ketone function at the interior of these ligands would reduce their level of non-specific binding, which might increase the selectivity of their uptake in vivo. The two compounds were prepared by total synthesis: compound 4 was prepared in fluorine-18 labeled form by [18F]fluorine ion displacement on a suitably protected methanesulfonate precursor followed by deprotection under acidic hydrogenolytic conditions; the isomer 5 was prepared from a protected alpha-keto trifluoromethanesulfonate precursor with deprotection under basic conditions as the final step. The binding affinity of these hexestrol derivatives for the estrogen receptor was determined by competitive radiometric binding assays at 0 and 25 degrees C, and their lipophilicity (as octanol-water partition coefficients, log P values) and non-specific binding were estimated. The log P values determined by a reversed phase HPLC method were higher, relative to estradiol, than those calculated by the fragment method of Rekker. In tissue distribution studies in immature (50 g) rats, both of these compounds showed selective uptake in estrogen target tissues. At 1 h, activity in the uterus reached the level of 2.5-3.0% of the injected dose per gram tissue, with uterus-to-blood and uterus-to-muscle ratios of 14-20 and 8-14, respectively. The uptake efficiency and selectivity of these fluoro-oxohexestrols in principal estrogen target tissues is less than that of fluorine-18 labeled steroidal estrogens we have prepared previously, but their receptor-mediated uptake in certain secondary target tissues is substantial. The specific and non-specific components of target tissue uptake of these two compounds appear to be directly related to their non-specific binding and their binding selectivity.

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Selective Birch-reduction of one of the phenolic rings of meso- or d,l-HES led to compounds 6a and 6b which exert a higher binding affinity to the androgen receptor as the respective parent HES. In vivo testing of 6a and 6b shows that 6a has the same potency in reducing accessory sex organ weights and testosterone levels in the intact mouse as has meso-HES, but strongly decreased estrogenic activity. Syntheses and testing of 7 having no ethyl side chains revealed the necessity of these groups for biological activity.

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The synthesis of the bis-acrylate 12, the bis-beta-chloropropionate 13 and the bis-beta-bromopropionate 14 of the "partial" antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane (7) is described. In the case of 13 and 14 the introduction of the beta-haloester-functions moderately reduces the estrogen receptor affinity of 7. However, it was quite strongly diminished in 12. The hydrolytic stability under in vitro-receptor-assay conditions decreases in the order 12 greater than 14 greater than 13. Compared with 7 the estrogenic potency of 12-14 is increased to a great extent. The title compounds cause a strong inhibition of the hormone-dependent MXT-M3.2 mouse mammary tumor.

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With the erythro-hexestrol derivative 2 as the starting material, a variety of cytotoxic linked hexestrol (HEX) compounds were prepared including the HEX-N-lost derivative 36, the HEX-(chloroethyl)nitrosourea 38, the HEX-cyclophosphamide 44, and the HEX-epoxide 68. Relative binding affinity to estradiol receptors were in the magnitude of 1%, similar to that of comparable diethylstilbestrol compounds. HEX derivatives with long polyether spacers (64, 65, 70, 71) showed no significant decrease in binding affinity in contrast to derivatives with other bulky side chains.

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Our approach to develop platinum complexes with a selective effect on the hormone-dependent MC by exchanging the two NH3 groups of cisplatin by an 1,2-bis(4-hydroxy-phenyl)ethylenediamine derivative which possesses estrogenic activity, was successful. The most interesting compound of this new platinum complex series, meso-(1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine)dichloroplati num(II) (meso-1-PtCl2) and its water soluble sulfatoplatinum(II) derivative (meso-1-PtSO4) were significantly more active on the DMBA-MC and the receptor positive MXT-MC than cisplatin and the related ligand 1,2-bis(2,6-dichloro-4-hydroxyphenyl)ethylenediamine (meso-1). According to our proposed mechanism of action, meso-1-PtX (X = Cl2 or SO4) should be enriched in the nuclei of mammary tumor cells, which possess an intact ER system (i.e. an intact cytoplasma nucleus translocation process), thereby causing very strong tumor growth inhibition. Preliminary studies of meso-1-PtSO4 on the DMBA-MC confirm this assumption. In the tumor tissue we found higher Pt-levels than in uterine tissue, which also contains ERs. The Pt-levels of the tumor tissue are much higher than those of skeletal muscle and of blood. In therapeutic dosages meso-1-PtSO4 does not cause kidney damages in rats.

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To develop an affinity label for the estrogen receptor that would be an estrogen agonist, rather than antagonist, we prepared several aziridine derivatives of the potent nonsteroidal estrogen hexestrol [3R,4S)-3,4-bis(4-hydroxyphenyl)hexane) bearing an aziridine function on the side chain. Three functional groups link the hexestrol ligand and the aziridine: a carbonyl group (ketone or ester), a thioether, or a methylene chain. The apparent competitive binding affinity of these derivatives for the estrogen receptor ranges from 1.8% to 25% that of estradiol, and most of them bind in a time-dependent, irreversible manner with the receptor, although the rate and efficiency of this binding vary widely, often with relatively small changes in structure. This is consistent with the irreversible attachment requiring a precise alignment of activating and reacting residues in the binding site of the receptor. The estrogenic and antiestrogenic activity of these aziridine derivatives was investigated in MCF-7 human breast cancer cells. Most of the compounds are agonists, with one being an antagonist. The derivative (6R,7S)-1-N-aziridinyl-6,7-bis(4-hydroxyphenyl)-5-nonanone (keto-nonestrol aziridine 3) appears to have the most ideal behavior of the estrogenic affinity labeling agents prepared: It is an agonist, and it binds to receptor irreversibly, efficiently, and quite rapidly.

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We have undertaken a staged development of certain estrogen-fluorophore conjugates, in order to prepare a fluorescent estrogen suitable for determination of the estrogen receptor content of individual cells. Since non-steroidal estrogens with bulky substituents are often more readily bound by receptor than their steroidal counterparts, we have investigated fluorophore conjugates with derivatives of the non-steroidal estrogen hexestrol [3R*, 4S*)-3,4-bis(4-hydroxyphenyl)hexane). On the basis of the receptor-binding affinity of model compounds, we prepared a prototypical set of three ring- and side-chain-substituted fluorescent hexestrol derivatives, whose binding and fluorescence properties ultimately led to the preparation of a series of side-chain-substituted nitrobenzoxadiazole derivatives. The compounds prepared have binding affinities for the estrogen receptors that range from ca. 1% to 5% that of estradiol, and they have very favorable fluorescence characteristics, similar to those of fluorescein.

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The influence of a symmetrical introduction of CH3 substituents in the alpha or beta positions of the 1,2-dialkyl-1,2-bis(4-hydroxyphenyl)ethane estrogens hexestrol (ethyl, HES) and octestrol (n-propyl, OCES) [isopropyl (1), tert-butyl (2), sec-butyl (3), isobutyl (4)] and the 1,2-dialkyl-1,2-bis(3-hydroxyphenyl)ethane antiestrogens metahexestrol (ethyl, MetaHES) and metaoctestrol (n-propyl, MetaOCES) [isopropyl (5), tert-butyl (6), sec-butyl (7), isobutyl (8)] on estradiol receptor (E2R) binding affinity and intrinsic activity is described. The synthesis of compounds 1-8 was accomplished by reductive coupling of (a) the corresponding alpha-alkylbenzyl alcohols with TiCl3/LiAlH4 and separation of the meso diastereoisomers (compounds 2-4, 7, and 8), (b) alpha-tert-butyl-3-methoxybenzyl chloride with CoCl2/EtMgCl and isolation of the meso configurated isomer (6), and (c) the isopropyl phenyl ketones with TiCl4/Zn and subsequent hydrogenation of the corresponding cis-hex-3-enes (compounds 1 and 5). The binding affinity of 1-8 to the calf uterine E2R was measured relative to that of [3H]E2 by a competitive binding assay. Compounds 1 and 5 showed relative binding affinity (RBA) values exceeding those of HES and MetaHES, respectively. All other derivatives showed RBA values smaller than the corresponding parent compounds. The intrinsic activity was monitored in terms of uterotrophic and antiuterotrophic activity. It is striking that the introduction of a CH3 group in the alpha positions of MetaHES and MetaOCES led to compounds with full intrinsic activity (5-7), i.e., estrogens without antiestrogenic properties. No correlation between E2R binding affinity and intrinsic activity was found.

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trans-1,2-Bis(trifluoromethyl)-1,2-bis(4- and 3-hydroxyphenyl)ethenes 2 and 4 were prepared by reductive coupling (TiCl4/Zn/pyridine) of the methoxy-substituted alpha, alpha, alpha-trifluoroacetophenones, separation of the resulting cis- and trans-stilbene derivatives, and ether cleavage with BBr3. The cis-stilbenes were catalytically hydrogenated to give meso-1,1,1,4,4,4-hexafluoro-2,3-bis(4- and 3-hydroxyphenyl)butanes 6 and 8. Compounds 2, 4, 6, and 8 showed 2- to 10-fold increased binding affinities for the estradiol receptor (E2R) and enhanced estrogenicity in the uterine weight test of the immature mouse compared to their unfluorinated analogues. Compound 8 exhibited a 46% inhibition of the estrone-stimulated uterine growth. Antitumor activity was evaluated with use of the transplantable, hormone-dependent MXT mammary tumor of the BD2F1 mouse. All compounds showed tumor growth inhibitory activity corresponding to their RBA values. The most interesting compound 8 led to a significant inhibition of the tumor growth on the DMBA-induced hormone-dependent mammary carcinoma of the Sprague-Dawley rat.

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Four fluorine- 18-labeled estrogens--16 alpha-[18F]fluoro-estradiol-17 beta (1), 16 beta-[18F]fluoro-estradiol-17 beta (2), (2R, 3S)-1-[18F]fluoro-2,3-bis(4-hydroxyphenyl)-pentane (1-[18F]fluoropentestrol) (3), and (3R, 4S)-1-[18F]fluoro-3,4-bis(4-hydroxyphenyl)hexane (1-[18F]fluorohexestrol) (4)--have been prepared by simple displacement reactions utilizing reactive trifluoromethane sulfonate (triflate) precursors and F-18 fluoride ion. All four fluoroestrogens have high affinity for the estrogen receptor. In immature female rats, they are taken up by target tissues, such as the uterus, with very high selectivity: uterus-to-blood ratios at 1 hr are: Compound 1, 39; Compound 2, 12; Compound 3, 13; and Compound 4, 19. Average uterus-to-blood ratios exceed 80 for Compound 1 at 2 hr. That the uptake process involves an estrogen-specific binder of limited capacity is demonstrated by the suppressive effect of coadministered unlabeled estradiol on target tissue uptake.

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The synthesis of symmetrically 2,2'-disubstituted butestrols [meso-2,3-bis(4-hydroxyphenyl)butanes] and of 6,6'-disubstituted metabutestrols [meso-2,3-bis(3-hydroxyphenyl)butanes] are described [2,2'-substituents: H (1), OH (2), F (3), Cl (4), Br (5), CH3 (6), and C2H5 (7); 6,6'-substituents: H (8), OH (9), Cl (10), and CH3 (11)]. Compounds 1-11 were obtained by reductive coupling of the corresponding 1-phenylethanols with TiCl3/LiAlH4 and separation of the meso diastereomers. The binding affinity of the test compounds to the calf uterine estrogen receptor was measured relative to that of [3H]estradiol by a competitive binding assay. With the exception of 9, all other compounds showed remarkably high relative binding affinity (RBA) values between 1.0 and 29% that of estradiol. Compounds 3 and 6 (RBA values: 15 and 29), as well as 10 and 11 (1.7 and 5.2), exceeded those of the corresponding unsubstituted compounds 1 and 8 (12 and 1.0). The compounds exhibited strong (3, 4, 6, and 7), moderate (1, 2, and 10), weak (11), or no (8) estrogenic activity in the uterine weight test of the immature mouse. Compounds 1, 2, 8, 10, and 11 showed antiestrogenic activity inhibiting the estrone-stimulated uterine growth (25-35% inhibition). Compound 11 led to a significant inhibition of the tumor growth when tested on the 9,10-dimethyl-1,2-benzanthracene induced, hormone-dependent mammary carcinoma of the Sprague-Dawley rat.

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The syntheses of symmetrically 4,4'-, 5,5'-, and 6,6'-disubstituted derivatives of the mammary tumor inhibiting antiestrogen metahexestrol [meso-3,4-bis(3-hydroxyphenyl)hexane] (1) are described [4,4'-substituents: F, (2), Cl (3), Br (4), I (5), CH2N (CH3)2 (6), CH3 (7), CH2OCH3 (8), CH2OC2H5 (9), CH2OH (10), NO2 (11), NH2 (12), N(CH3)2 (13), COCH3 (14), and C2H5 (15); 5,5'-substituents: OH (16) and Cl (17); 6,6'-substituents: OH (18), F (19), Cl (20), and CH3 (21)]. The synthesis of 1-3, 16, and 19 was accomplished by reductive coupling of the propiophenones with TiCl4 /Zn and subsequent hydrogenation of the cis-3,4- diphenylhex -3- enes . Compounds 17, 18, 20, and 21 were synthesized by coupling the 1-phenyl-1-propanols with TiCl3 /LiAlH4 and separation of the meso diastereomers, while 4-15 were obtained by substitution of metahexestrol . The binding affinity of these compounds to the calf uterine estrogen receptor was measured relative to that of [3H]estradiol by a competitive binding assay. The test compounds showed relative binding affinity (RBA) values between 15 and less than 0.01% that of estradiol. Only compound 21 showed an estrogen receptor binding affinity exceeding that of metahexestrol (15 and 10%, respectively). Compounds exhibiting RBA values of greater than 0.5% were evaluated in the mouse uterine weight test. They showed a similar (2 and 12), slightly increased (19 and 21), or strongly enhanced (7 and 20) estrogenicity compared to that of metahexestrol . Compounds 1, 2, 7, 12, and 21 exhibited antiestrogenic activity inhibiting the estrone-stimulated uterine growth (24 to 60% inhibition).

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The reaction of ethyl chloroformate with amino compounds has been evaluated as a simple route to carbon-11 labeling of steroid hormone-receptor-based imaging agents. Both a 17 beta-amino analogue of estradiol and an aminoethyl derivative of the nonsteroidal estrogen hexestrol with potential affinity for the estrogen receptor were studied. The unlabeled carbamate derivatives of the amino estrogens were prepared by standard methods, and the 11C-labeled analogues were synthesized from [11C]ethyl chloroformate, generated by purging ethanol with [11C]phosgene. Both carbamates showed weak in vitro binding affinity for the estrogen receptor, and only the 11C-labeled hexestrol exhibited a small but significant estrogen-responsive uterus uptake in immature rats.

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The positron-emitting, non-steroidal estrogen (2R*, 3S*)-1-[18F]fluoro-2,3-bis(4-hydroxyphenyl)pentane [( 18F]-fluoronor-hexestrol), has been prepared by fluoride ion displacement on a labile trifluoromethanesulfonate (triflate) derivative of a suitably protected precursor, followed by removal of the aryl triflate groups with lithium aluminum hydride and purification by HPLC. In immature female rats, this compound is taken up selectively by the uterus and is retained for prolonged periods, due to its binding to the estrogen receptor. This compound and related 18F-labeled estrogens thus appear to be promising agents for imaging estrogen receptor-positive breast tumors in humans.

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The syntheses of symmetrically 3,3'- and 2,2'-disubstituted meso hexestrol derivatives are described [3,3'-substituents: OH (1), F (2), Cl (3), Br (4), I (5), CH2N(CH3)2 (6), CH3 (7), CH2OCH3 (8), CH2OC2H5 (9), CH2OH (10), NO2 (11), NH2 (12), N(CH3)2 (13), COCH3 (14), and C2H5 (15); 2,2'-substituents: OH (16), F (17), Cl (18), Br (19), CH3 (20), and C2H5 (21)]. The synthesis of 1-3 was accomplished by reductive coupling of the propiophenones with TiCl4/Zn and subsequent hydrogenation of the cis-3,4-diphenylhex-3-enes. Compounds 4-15 were obtained by substitution of hexestrol, while compounds 16-21 were synthesized by coupling the 1-phenyl-1-propanols with TiCl3/LiAlH4 and separation of the meso diastereomers. The binding affinity of these compounds to the calf uterine estrogen receptor was measured relative to that of [3H]estradiol by a competitive binding assay. All test compounds showed relative binding affinity (RBA) values between 32 and less than 0.01% that of estradiol. Only meso-3,4-bis(2,4-dihydroxyphenyl)hexane (16) showed an estrogen receptor binding affinity comparable to that of hexestrol (32 and 27%, respectively). Compounds exhibiting RBA values of greater than 5% were evaluated in the mouse uterine weight test. All of them showed uterotrophic activity. Compounds 2, 7, 16, 17, and 20 were strongly active in very small doses (1 microgram per animal per day), while 1 and 12 produced full uterotrophic effects only in high doses and inhibited the estrone-stimulated uterine growth strongly in small doses (59 and 78% inhibition, respectively).

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A series of nonsteroidal, side-chain functionalized estrogens based on (3R*,4S*)-3,4-bis(4-hydroxyphenyl)hexane (hexestrol) and (2R*,3S*)-2,3-bis(4-hydroxyphenyl)pentane (norhexestrol) has been prepared; these include amide, diazo ketone, ester, alcohol, ketone, fluoro, bromo, iodo, and saturated hydrocarbon derivatives. Analysis of the binding affinity of these compounds to the uterine estrogen receptor, measured by competitive binding assay, reveals trends that can be related to the steric size, the hydrophobicity, and the hydrogen bond accepting character of the side-chain substituents. Comparison of binding affinities between norhexestrol and hexestrol derivatives indicates that, in general, the norhexestrols show significantly higher receptor binding affinities, making this series of compounds ideally suited as functional probes for the estrogen receptor.

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