Synthesis of benzoylbenzamide derivatives of 17α-E-vinyl estradiol and evaluation as ligands for the estrogen receptor-α ligand binding domain.

A series consisting of substituted benzoylbenzamide derivatives of 17α-E-vinyl estradiol 6a-i and 7a-d was prepared in good overall yields from the corresponding novel iodinated benzoylbenzamide precursors using Pd(0)-catalyzed Stille coupling. Biological evaluation using competitive binding assays indicated that all compounds were effective ligands for the ERα- and ERß-LBD (RBA = 0.5-10.0% of estradiol). Most of the compounds expressed lower stimulatory (agonist) potency (RSA <0.2-0.5%) compared to their binding affinity, however, the meta-substituted isomer 6h demonstrated a level of efficacy (RSA = 5.7%) comparable to its affinity (RBA = 9.5%). Docking studies of 6b, 6h, and 6i with the 2YAT crystal structure suggested that higher affinity and efficacy of 6h are due to an effective set of interactions with exposed receptor sidechains not observed with the ortho- and para- isomers. In this binding model, the terminal ring of the ligand is exposed to the solvent space, which would explain both the small variation in RBA values and the narrow SAR for the diverse structural features.

Convergent synthesis of a steroidal antiestrogen-mitomycin C hybrid using "click" chemistry.

A convergent synthesis of a novel estrogen receptor-targeted drug hybrid was developed based on structures of the potent anti-proliferative mitomycin C and the steroidal anti-estrogen RU 39411. The steroidal antiestrogen was prepared with an azido-triethylene glycoloxy linker while the mitomycin C derivative (porfirimycin) incorporated a complementary 7-N-terminal alkyne. The two components were ligated using the Huisgen [3 + 2] cycloaddition ("click") reaction. Preliminary biological assays demonstrated that the final hybrid compound retained both potent anti-estrogenic and anti-proliferative activities.

Synthesis and evaluation of 11ß-(4-substituted phenyl) estradiol analogs: transition from estrogen receptor agonists to antagonists.

INTRODUCTION: As part of our program to develop estrogen receptor (ER) targeted imaging and therapeutic agents we chose to evaluate 11ß-substituted estradiol analogs as a representative scaffold. Previous synthetic studies provided an entry into this class of compounds and other work indicated that 11ß-(substituted aryl) estradiol analogs were potent antagonists of the ER. Little information existed about the specific structural features involved in the transition from agonism to antagonism for the 11ß-aryl estradiol analogs or their potential as scaffolds for drug conjugation. METHODS: We prepared and characterized a series of 11ß-(4-Substituted phenyl) estradiol analogs using modifications of existing synthetic methods. The new compounds, as well as standard steroidal agonists and antagonists, were evaluated as competitive ligands for the ERß-LBD. Functional assays used the induction of alkaline phosphatase in Ishikawa cells to determine potency of the compounds as ER agonists or antagonists. RESULTS: The synthetic strategy successfully generated a series of compounds in which the 4-substituent was sequentially modified from hydroxyl to methoxy to azidoethoxy/N,N-dimethylaminoethoxy and eventually to a prototypical 1,4-naphthoquinone-containing moiety. The new compounds all retained high relative binding affinity (RBA) for the ERα-LBD, ranging from 13-83% that of estradiol. No subtype selectivity was observed. More importantly, the transition from agonist to antagonist activity occurs at the 4-methoxy stage where the compound is a mixed antagonist. More notably, antagonism appeared to be more dependent upon the size of the 11ß-substituent than upon the nature of the terminal group CONCLUSIONS: We have developed a synthetic strategy that provides facile access to potent 11ß-(4-substituted phenyl) estradiol analogs. The resultant compounds retain high affinity for the ERα-LBD and, more importantly, demonstrate potent antagonist activity in cells. Large functionalities distal to the 11ß-phenyl ring had little additional effect on either affinity or efficacy, suggesting the incorporation of diverse imaging or biologically active groups can be attached without significantly compromising the ER-binding capacity. Future studies are in progress to exploit the 11ß-aryl estradiol analogs as potential drug delivery systems and imaging agents.

Targeting the estrogen receptor with metal-carbonyl derivatives of estradiol.

As part of our program to develop new probes for the estrogen receptor binding domain, we prepared and evaluated a novel 17α-(rhenium tricarbonyl bipyridyl) vinyl estradiol complex. Preparation of the final compound was achieved using the Stille coupling between the preformed brominated rhenium tricarbonyl bipyridine complex and the tributylstannyl vinyl estradiol. Competitive receptor binding assays and stimulatory assays demonstrated that the final complex retained affinity and efficacy comparable to the corresponding pyridyl vinyl estradiol analog, but lower than that of the phenyl vinyl estradiol analog.