Chemically reactive estrogens: synthesis and estrogen receptor interactions of hexestrol ether derivatives and 4-substituted deoxyhexestrol derivatives bearing alkylating functions

Abstract

A series of chemically reactive derivatives of the nonsteroidal estrogen hexestrol have been synthesized as potential affinity labels for the estrogen receptor or as cytotoxic agents with selective activity against receptor-containing cells. These compounds are hexestrol ethers with halo ketone, halohydrin, or epoxide functions or 4-substituted deoxyhexestrols with halo ketone, benzyl halide, nitro, azide, sulfonyl fluoride, or sulfonyl azide groups. The alkylating activity of the electrophilic derivatives was measured using the colorimetric reagent nitrobenzylpyridine, the bromo derivatives being considerably more reactive than the chloro ones. Their reversible binding to the lamb uterine estrogen receptor was measured by competitive binding assays, and their irreversible reaction with receptor was measured by exchange assays that determine the rate and extent of receptor inactivation. In general, monoetherification of hexestrol or substitution of deoxyhexestrol produces compounds with relatively low affinity for the estrogen receptor (0.3-10% that of estradiol). Most of the electrophilic derivatives are rapid and effective inactivators of receptor (24-70% inactivation within 0.5-5 h at 25 degrees C). Of the photosensitive derivatives, 4-azidodeoxyhexestrol appears to be the most efficient receptor inactivator (49%). The high reactivity of these compounds toward the estrogen receptor and the lack of interference by their reaction with other cellular nucleophiles suggest that these compounds may be useful as affinity-labeling agents or as selective cytotoxic agents in intact systems.

Comparative QSAR Analysis of Estrogen Receptor Ligands

“…Katzenellenbogen's group synthesized a series of 4-substituted deoxyhexestrol derivatives and measured their relative receptor binding affinities with estrogen receptor in lamb uterine cytosol at 0 °C − (Table ). From this set, we obtained eq 12, which has negative correlations with the size parameter MR and an electronic term σ.…”

Combined Biophysical Chemistry Reveals a New Covalent Inhibitor with a Low-Reactivity Alkyl Halide

“…Obviously, the demonstration of the capacity of a common and accessible functional group like a primary alkyl halide to act as a reagent for the N-alkylation of an enzyme could demonstrate the viability of such a weak electrophile group for the development of a new type of selective CI. In fact, very few documented examples of an enzyme alkylation by a primary alkyl halide derivative have been reported to date, including a case of O -alkylation from a carboxylate group of Asp 106 residue for haloalkane dehalogenase tagging and a suspected S-alkylation from Met 193 of 16α-bromopropyl-E2 leading to an irreversible inhibition of 17β-HSD1. , Importantly, the primary alkyl halide electrophile group must not be confused with activated alkyl halide units, like the highly reactive N-ethylhalide of “nitrogen mustard” agents, which form a covalent bond via the formation of an intermediate aziridinium very reactive species that reacts with the DNA nitrogenous base, or with benzyl halide , and α-halo ketone groups, which are not specific, albeit useful in labeling affinity agents for enzyme characterization. , …”

“…In fact, very few documented examples of an enzyme alkylation by a primary alkyl halide derivative have been reported to date, including a case of Oalkylation from a carboxylate group of Asp 106 residue for haloalkane dehalogenase tagging 34 and a suspected S-alkylation from Met 193 of 16α-bromopropyl-E2 leading to an irreversible inhibition of 17β-HSD1. 35,36 Importantly, the primary alkyl halide electrophile group must not be confused with activated alkyl halide units, like the highly reactive N-ethylhalide of "nitrogen mustard" agents, which form a covalent bond via the formation of an intermediate aziridinium very reactive species that reacts with the DNA nitrogenous base, 37 or with benzyl halide 38,39 and α-halo ketone 40 groups, which are not specific, albeit useful in labeling affinity agents for enzyme characterization. 41,42 Because no example of N-alkylation between an enzyme and a primary alkyl halide has been reported to date and also to rule out the possibility of the Met 279 of 17β-HSD1 to act as nucleophile over the primary alkyl halide (Figure S1), we thus seized this opportunity and engaged cocrystallization experiments of PBRM with 17β-HSD1 to prove the capacity of such a weak electrophile to form a covalent bond with the suspected His 221 residue, an AA rarely exploited in design of CI drugs.…”

Preparation of 7-(1,3,4-oxadiazolyl)-6,14-endo-etheno-6,7,8,14-tetrahydrothebaines and related compounds as potential analgesics

“…Many compounds containing the bridged thebaine (1, R = CH3) or bridged oripavine (1, R = H) skeleton are potent analgesics, and the nature of the C-7 substituent has an important bearing on this activity.1 Recently, we reported the synthesis of 7a-(2,3-dihydro-2-oxo-l,3,4-oxadiazol-5-yl)-6,14-endo-etheno-6,7,8,14-tetrahydrothebaine (2a, X = 0) and the related thione 2b (X = S).2 2a, X = O b, X = S Prior to our work, one report had appeared in the literature describing bridged thebaines and oripavines with other heterocyclic rings attached at C-7, viz., 5-pyrazolyl, 5-isoxazolyl, and 2or 4-pyrimidyl, which showed analgesic activity. 3 We therefore wished to develop syntheses of 7-(l,3,4-oxadiazolyl)-6,14-erodo-ethenotetrahydrothebaines by mild routes that would avoid ring-opening complications, which are the principle problems associated with the chemistry of the bridged thebaine unit,4 and to study their pharmacology.…”

“…The required starting materials 5a and 5b were obtained by refluxing 3 with the relevant carboxylic acid. Subsequently, heating 5a in acetic anhydride for 4.5 h did not furnish the expected oxadiazole 4b (mp 204-205 °C).…”