Conformational Analysis of Bivalent Estrogen Receptor Ligands: From Intramolecular to Intermolecular Binding

Abstract

The estrogen receptor binding affinities of bivalent raloxifene ligands tethered by flexible spacers of different lengths have been evaluated in vitro. Two bivalent binding modes, intra- and intermolecular, were hypothesized to explain their different binding properties. The binding affinities of these bivalent ligands in an aqueous environment are influenced by their conformations, which can be determined by 2D NMR and UV spectral methods. Moreover, computer modeling and simulations were performed to explain the binding modes of these bivalent ligands and to estimate the conformational entropy difference between their unbound and bound states. It was found that bivalent ligands tethered by long spacers had weaker binding affinities because of the shielding of the binding moieties that results from their folded conformations; those tethered by short spacers had stronger affinities because they exposed their ligands to the receptor.

Nonsteroidal Bivalent Estrogen Ligands: An Application of the Bivalent Concept to the Estrogen Receptor

“…Based on our results and others, 19–26 we can reach a number of conclusions regarding factors that influence bivalent ER-ligand interaction. First, an estrogen antagonist (e.g., RAL or OHT) induces an antagonistic ER-binding conformation, where the displacement of helix-12 creates a channel through which certain substituents can escape the confines of the cognate binding site in the direction of the ER dimer interface.…”

“…26 The intrinsic activity (IA) of each ligand was assayed at 10μM. Ligands 1 – 7 showed pure agonistic activity that was related to spacer length: Ligands 1 and 4 – 6 with spacer lengths of 34.8–39.8Å had less than 50% IA values on ERα, while on ERβ only ligands 1 and 5 have similar IA values.…”

Design, preparation, and selection of DNA-encoded dynamic libraries

“…2d); 74 dimeric raloxifene ligands are able to bind to the two binding pockets on estrogen receptor dimers. 61,75,76 Similar to the biotin ligand series, a significant fluorescence decrease was observed in the presence of the specific target ER and the bivalent raloxifene duplex (Fig. 2e).…”

An improved synthesis of a fluorophosphonate–polyethylene glycol–biotin probe and its use against competitive substrates

“…This was then subjected to a two-step procedure to provide the novel iodo ether 4b . Thus, tosylation of 3 utilizing a slight modification of literature conditions [15] gave 4a , which was subjected to Finkelstein conditions by utilizing a procedure reported for a related compound [16] to afford 4b in a combined 90% yield. The phosphonate moiety was installed under standard Arbuzov conditions by heating 4b under reflux in neat triethyl phosphite for 1 h to provide novel intermediate 5 in 92% yield following purification by column chromatography.…”

“…1-Phenyl-2,5,8,11-tetraoxatridecan-13-yl 4-methylbenzenesulfonate (4a): This compound was made by a slight modification of the literature procedure [15]. An ice-cold solution of tetraethylene glycol monobenzyl ether ( 3 ; 13.9 g, 48.9 mmol; made by the procedure of Jiang et al [14]) in 70 mL of THF was treated with KOH (9.85 g, 171.1 mmol) dissolved in 50 mL of water.…”