Synthesis and Evaluation of 17α-20E-21-(4-Substituted phenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17β-diols as Probes for the Estrogen Receptor α Hormone Binding Domain

Abstract

As part of our program to develop probes for the hormone binding domain of the estrogen receptor alpha (ERalpha), we prepared a series of 4-para-substituted phenylvinyl estradiol derivatives using a combination of solution and solid-phase Pd(0)-catalyzed methods. The compounds 5a-j were evaluated for their binding affinity using the ERalpha hormone binding domain (HDB) isolated from transfected BL21 cells. The results indicated that although the new compounds were somewhat lower in relative binding affinity (RBA at 25 degrees C is 1-60%) than estradiol (100%), most had higher affinity than the unsubstituted parent phenylvinyl estradiol (RBA = 9%). Because the substituents did not generate a structure-activity relationship directly based on physicochemical properties, the series was evaluated using molecular modeling and molecular dynamics to determine key interactions between the ligand, especially the para substituent, and the protein. The results suggest that the observed relative binding affinities are directly related to the calculated binding energies and that amino acids juxtaposed to the para position play a significant but not dominant role in binding. In conclusion, we have identified the 17alpha-E-(4-substituted phenyl)vinyl estradiols as a class of ligands that retain significant affinity for the ERalpha-HBD. In particular, 4-substitution tends to increase receptor affinity compared to the unsubstituted analogue, as exemplified by 5e (4-COCH(3)), which had the highest RBA value (60%) of the series. Palladium(0)-catalyzed coupling reactions on solid support or in solution using suitably substituted iodo arenes and 17alpha-E-tributylstannylvinyl estradiols offer a flexible approach to their preparation. Molecular modeling studies of the receptor suggest that there exists additional ligand accessible regions within the ERalpha-HBD to generate interactions that may enhance receptor affinity or modify efficacy in developing new therapeutic agents. Studies to undertake modification in the properties and/or position of the aryl substituents in subsequent series to further define that role are in progress.

In-silico Screening using Flexible Ligand Binding Pockets: A Molecular Dynamics-based Approach

“…Figure 6 shows the stick model representation of the flexible binding pocket residues(forthecrystalstructureandthe3 nsMDGS) identified from the side chain torsional angle (v 1 , v 2 ) analysis. We found that both backbone and the side chains for residues I326, M421, H524 have maximum variations between MDGS and the crystal structure, which is in accordance with the earlier reported studies [38][39][40]. Superposition of all the MDGS reveal that the LBP corresponding to the A-ring of the estrogen have minimal structural differences when compared to that of the D-ring binding pocket.…”

Synthesis and biological evaluation of a fluorescent analog of phenytoin as a potential inhibitor of neuropathic pain and imaging agent

“…The SHAKE algorithm was used to fix the bonds involving hydrogen. 32 The protocol for the molecular dynamics simulation is described below: The total charge of the system was neutralized by addition of a chloride ion. The system was solvated in a 12 Å cubic box of water where the TIP3P model 8 was used.…”

Synthesis and evaluation of 17α-(dimethylphenyl)vinyl estradiols as probes of the estrogen receptor-α ligand binding domain

“…[1-4] Analysis of the E-(4-substituted phenyl)vinyl estradiols indicated that there existed within the LBD significant steric tolerance toward 4-substituent and that some polar influences were present. [5] Comparison with the corresponding Z-(4-substituted phenyl)vinyl isomers suggested that the two phenyl vinyl moieties accessed different regions of the LBD, leading to different structure-activity relationships. [6] Subsequent examination of the E-(2-,3-, and 4-trifluoromethylphenyl)vinyl estradiols demonstrated significant dependence on substitution patterns, as the 2-isomer was more potent in vitro as well as in vivo .…”