Synthesis and evaluation of 11beta-substituted 21-chloro/iodo-(17alpha,20E/Z)-19-norpregna-1,3,5(10),20-te traene-3, 17beta-diols: high-affinity ligands for the estrogen receptor.

We have synthesized six new estrogens substituted at the 11beta-position with a methoxy or vinyl group and at the 17alpha-position with an (E)- or (Z)-chloro/iodovinyl moiety. The products were obtained in good overall yields from the corresponding tri-n-butylstannylvinyl intermediates using the electrophilic halodestannylation methodology. The six new ligands were compared to the 11beta-unsubstituted chloro/iodovinyl derivatives and the 11beta-methoxy (E)- and (Z)-iodovinyl estrogens to evaluate the effects of 11beta-substitution and 20E/Z-stereochemistry. While all the compounds exhibited high affinity for the estrogen receptor, the 20Z-isomers demonstrated higher affinity than the corresponding 20E-isomers. In addition, the presence of the lipophilic 11beta-substituent was favored over either no substituent or a polar (methoxy) group. Within each isomeric series, the presence of the 21-halo substituent had different effects. For the 20E-series, the 21-chloro products had a higher affinity than the 21-iodo analogue, whereas for the 20Z-series the effect was reversed. These results provide additional insights into the interaction of substituted estradiols with the hormone binding domain of the estrogen receptor.

Novel high-affinity steroidal estrogenic ligands: synthesis and receptor binding of 11 beta-vinyl-17 alpha-E/Z-phenylselenovinyl estradiols.

Previous studies from our laboratory demonstrated separately the tolerance of the estrogen receptor for the 17 alpha-phenylselenovinyl substituent and the enhancement of affinity imparted by the 11 beta-vinyl moiety. Our recent publication suggested that the two groups could be combined within a single structure and retain high affinity for the estrogen receptor. As a result, we have prepared in good overall yields the E- and Z-isomers of 11 beta-vinyl-17 alpha-phenylselenovinyl estradiol. Evaluation of the new steroids with receptor isolated from lamb cytosol indicated that both isomers are poorer ligands than estradiol at 4 degrees C, but both are better than estradiols. at 25 degrees C. This behavior had not been observed for the 11 beta-unsubstituted 17 alpha-E/Z phenylselenovinyl estradiols. Of particular interest was the observation that, unlike previous isomer pairs, the E-isomer possessed a greater affinity than the Z-isomer. The results suggest that relatively small changes in structure may impart significant differences in the interactions with the receptor and provide the basis for further ligand design.

Stereochemical probes for the estrogen receptor: synthesis and receptor binding of (17 alpha,20E/Z)-21-phenyl-19-norpregna-1,3,5(10), 20-tetraene-3,17 beta-diols.

Previous studies from our laboratory using 17 alpha-E- and 17 alpha-Z-halovinyl and phenylthiovinyl estradiols demonstrated a marked preference for the Z stereochemistry and a significant steric tolerance for the Z-vinyl substituent. To further explore the extent of that stereochemical preference and steric tolerance we have prepared stereoselectively the 17 alpha-E- and 17 alpha-Z-phenylvinyl estradiols (E- and Z-styrylestradiols). The results, in addition to demonstrating a facile preparation of the target compounds, supported the previously observed stereochemical and steric effects. The relative binding affinities for the Z isomer were 3-4 fold greater than the E isomer at both 4 degrees C and 25 degrees C, and only one-half to one-fourth those of estradiol under similar conditions. The developing model for ligand-accessible space within the estrogen receptor suggests that Z-phenylvinyl estradiols may provide interesting and useful probes for mapping the receptor.

Synthesis and estrogen receptor binding of (17 alpha, 20E)- and (17 alpha, 20Z)-21-phenylthio- and 21-phenylseleno-19-norpregna-1,3,5(10),20-tetraene-3,17 beta-diols.

Previous studies from our laboratory using 17 alpha-E- and 17 alpha-Z-halovinyl estradiols demonstrated a marked enhancement of receptor binding by the Z-isomers. This suggested tolerance at the 17 alpha-position was not previously observed by investigations using 16 alpha and 17 alpha-substituted estradiols. Because of the synthetic access provided by vinyl tin chemistry, we prepared the 17 alpha-E and Z-phenylthiovinyl and phenylselenovinyl estradiols and compared their binding characteristics to those of the previously reported 16 alpha/17 alpha-phenylseleno and methylseleno estradiols. The results, in addition to demonstrating a facile preparation of the target compounds, indicated that significant receptor affinity was retained by these compounds (relative binding affinity = 24.5-117). The highest affinity was demonstrated by the 17 alpha-Z-phenylthiovinyl estradiol 5a, which, by molecular modeling, exhibited a significantly different molecular conformation from the corresponding 17 alpha-E-phenylthiovinyl isomer or the 17 alpha-phenyl-thioethynyl analog. The current series possessed better binding characteristics than the phenylseleno and methylseleno estradiols but somewhat poorer binding than the 17 alpha-E/Z-halovinyl series. The observations suggest that some steric limitations exist in a portion of the 17 alpha-region, and that the region is better accessed by compounds possessing Z-vinyl stereochemistry.

11 beta-substituted estradiol derivatives. 2. Potential carbon-11- and iodine-labeled probes for the estrogen receptor.

Four new classes of 11 beta-substituted estradiol and estriol derivatives (cyanoalkyl, ethynyl, propynyl, and iodovinyl) have been synthesized, and their binding affinity for the estrogen receptor has been evaluated. The binding affinity values indicate that the estrogen receptor has tolerance for estradiol derivatives bearing 11 beta-groups whose size, rigidity, and polarity are limited. The estradiol derivatives have higher affinity than the estriol derivatives. The potential of these agents as imaging agent for estrogen receptor-positive breast tumors is discussed. On the basis of the results of this and a previously reported study (Napolitano, E.; Fiaschi, R.; Carlson, K. E.; Katzenellenbogen, J. A. 11 beta-Substituted Estradiol Derivatives, Potential High-Affinity Carbon-11-Labeled Probes for the Estrogen Receptor: A Structure-Affinity Relationship Study. J. Med. Chem. 1995, 38, 429-434), a general strategy for designing high-affinity probes for the estrogen receptor is proposed.

11 beta-Substituted estradiol derivatives, potential high-affinity carbon-11-labeled probes for the estrogen receptor: a structure-affinity relationship study.

In view of their possible development as carbon-11-labeled receptor-based radiotracers for imaging estrogen-responsive breast tumors, we have synthesized a series of estradiols (1), estriols (2), 11 beta-ethylestradiols (3), 11 beta-ethylestriols (4), 11 beta-methoxyestradiols (5), and 11 beta-methoxyestriols (6), differing in the type of substituent R present at the 17 alpha-position (a, -H; b, -CH3; c, -C identical to CH; d, -C identical to CCH3; e, -Ph; f, -CH = CHMe cis), and measured their binding affinity for the estrogen receptor relative to estradiol (RBA). As expected, all the derivatives having an 11 beta-ethyl substituent have good binding properties (3a-d, 4a-d, RBA (25 degrees C): 109-3000%), and among them there are several promising candidates for carbon-11 labeling. Moxestrol (RBA (25 degrees C) = 185%) and its corresponding estriol derivative (4c, RBA (25 degrees C) = 20%) were the analogs having the highest affinity in the 11 beta-methoxyestradiol (5a-f) and 11 beta-methoxyestriol (6a-e) series, respectively; other analogs (R = Me, C identical to CMe, Ph, or cis-CH = CHMe) had uniformly lower RBA values.

Structure-activity relationships of estrogenic ligands: synthesis and evaluation of (17 alpha, 20E)- and (17 alpha, 20Z)-21-halo-19-norpregna-1,3,5(10),20-tetraene-3,17 beta-diols.

As part our program to probe the molecular requirement for estrogen-receptor binding we undertook the synthesis and evaluation of the 17 alpha,E and 17 alpha,Z halovinyl estradiols. By use of an improved variation of the existing synthetic strategy, the targeted compounds were prepared stereospecifically and in 92-98% yields from the corresponding 17 alpha,E or 17 alpha,Z [(tri-n-butylstannyl)vinyl]estradiol 3-acetates. The novel estradiol derivatives were evaluated for their relative binding affinity (RBA) for the estrogen receptor with use of a rat uterine preparation. The results demonstrated a marked difference between the E and Z isomers and among the halogen employed. The Z isomers possessed significantly higher RBA values and the larger halogens (I, Br) were more effective than the smaller Cl substituent. These results modify the previous interpretations of estrogen-receptor binding for steroidal ligands. As a result, our design of (radio)halogenated ligands will incorporate this concern for Z vs E stereochemistry.

Progestin-rhenium complexes: metal-labeled steroids with high receptor binding affinity, potential receptor-directed agents for diagnostic imaging or therapy.

In order to investigate the possibility of developing diagnostic imaging agents for steroid-positive tumors that are labeled with the readily available radionuclide technetium-99m, we prepared four conjugate systems in which a progestin is linked to a metal chelate system. Three of these are bis-amino bis-thiol (BAT or N2S2) systems and are linked through carbon-21 of progesterone or the 17 alpha- or 11 beta-position of a nortestosterone type progestin. The fourth, an amino-amido-thiol-alcohol chelate (N2OS) system, is linked at the 16 alpha,17 alpha-positions of a dihydroprogesterone. As a model for technetium-labeled complexes, all four chelate systems were converted to their oxo-rhenium complexes. Of the four possible diastereomers in the 16 alpha,17 alpha-system, only one was isolated, while of the four possible diastereomers in the other systems, a syn pair and an anti pair (linker methylene vs rhenium-oxo, relative to the N2S2 plane) were separated in the 17 alpha-substituted series, a syn pair was isolated in the 21-substituted series, and a syn pair and the two individual anti diastereomers were separated in the 11 beta-substituted series. In competitive radiometric receptor binding assays, the 21-, 17 alpha-, and 16 alpha,17 alpha-linked systems had low affinity for the progesterone receptor (less than 0.3% that of promegestone (R5020) or 2% that of progesterone). By contrast, the two anti diastereomers of the 11 beta-linked system had affinities that were 10% and 44% that of R5020 (or 64% and 283% that of progesterone) and the syn pair had an affinity 25% that of R5020 (or 161% that of progesterone). The latter finding indicates that it is possible to prepare metal-labeled steroids that retain high affinity for steroid receptors. These and related systems, when complexed with radioactive metals, may be useful in vivo as receptor-directed agents for diagnostic imaging or therapy of steroid receptor-positive tumors.

Synthesis and estrogen receptor binding of novel 11 beta-substituted estra-1,3,5(10)-triene-3,17 beta-diols.

As part of our program to develop estrogenic radioligands for use in nuclear medicine, a study was undertaken to investigate the effect of substituents on the receptor affinity of putative radiochemicals. In the study a synthetic strategy directed toward the introduction of an 11 beta-(fluoroethyl) substituent was devised. The target compound 9 was prepared via a five-step procedure starting from 11 beta-vinylestrone 3-acetate (4) in an overall 43% yield. The stereochemistry of the 11 beta-vinyl moiety was established by X-ray crystallography. The final product and several analogues, 11 beta-ethyl-, -vinyl-, and (hydroxyethyl)estradiols (11, 5, and 12), were evaluated for their estrogen receptor binding affinity. The results indicate that the target compound and several 11 beta-substituted analogues possess relative binding affinities greater than of estradiol and its 16 alpha-fluorinated derivatives. The manner in which the target compound 9 was prepared is amenable to use with 18F incorporation.

Estrogen receptor binding characteristics of 1,11 beta-ethanoestradiol: effect of a 1,11 beta-bridge on steroidal estrogen.

As part of an ongoing program to develop high affinity estrogenic ligands we have synthesized the 11 beta-vinyl, 11 beta-ethyl- and 1,11 beta-ethanoestradiols. Because the 1,11 beta-ethano-estradiol had not been previously reported in the literature, the investigation of its receptor binding characteristics would provide valuable insight into the effect of 1/11 beta-substitution. The data obtained in this study indicate that although significant estrogen receptor affinity is present for the 1,11 beta-ethano derivative, the RBA values, 5-22.4%, were far less than those observed (5-300-fold less) for the corresponding 11 beta-ethyl and 11 beta-vinyl estradiols and less than those for the 1-methyl and 11 beta-methyl estradiols. These results suggest that the orientation that the 11 beta-substituent must occupy is directed away from the A-ring and that substituents in the 1-11 pocket produce a detrimental effect on receptor interactions.