Conformational Studies on (17α,20Z)-21-(X-Phenyl)-19-norpregna-1,3,5(10),20-tetraene-3,17β-diols Using 1D and 2D NMR Spectroscopy and GIAO Calculations of ¹³C Shieldings

Abstract

Differences in agonist responses of the novel estrogen receptor ligands (17alpha,20Z)-(p-methoxyphenyl)vinyl estradiol (1), (17alpha, 20Z)-(o-alpha,alpha,alpha-trifluoromethylphenyl)vinyl estradiol (2), and (17alpha,20Z)-(o-hydroxymethylphenyl)vinyl estradiol (3) led us to investigate their solution conformation. In competitive binding assay studies, we observed that several phenyl-substituted (17alpha, 20E/Z)-(X-phenyl)vinyl estradiols exhibited significant estrogen receptor binding, but with variation (RBA (1) = 20; RBA (2) = 23; RBA (3) = 140 where estradiol RBA = 100) depending on the phenyl substitution pattern. Because the 17alpha-phenylvinyl substituent interacts with the key helix-12 of the ligand binding domain, we considered that differences in the preferred conformation of 1-3 could account for their varying binding affinity. 2D NMR experiments at 500 MHz allowed the complete assignment of the (13)C and (1)H spectra of 1-3. The conformations of these compounds in solution were established by 2D and 1D NOESY spectroscopy. A statistical approach of evaluating contributing conformers of 1-3 from predicted (13)C shifts correlated quite well with the NOE data. The 17alpha substituents of 1 and 2 exist in similar conformational equilibria with some differences in relative populations of conformers. In contrast, the 17alpha substituent of 3 exists in a different conformational equilibrium. The similarity in solution conformations of 1 and 2 suggests they occupy a similar receptor volume, consistent with similar RBA values of 20 and 23. Conversely, the different conformational equilibria of 3 may contribute to the significant binding affinity (RBA = 140) of this ligand.

Structural plasticity in the oestrogen receptor ligand‐binding domain

“…It should also be noted that the conformation of TFMPV‐E2 in the crystal structure differs significantly from both the liquid and gas‐phase lowest energy conformations (Sebag et al , 2000). Therefore, generation of the observed ligand–receptor complex involves adaptive responses by both partners in this process.…”

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

“…[46][47][48][49][50][51][52] We had synthesized several Z-phenylvinyl estradiols and examined their preferred solution and gas-phase conformations using a combination of NMR and computational methods. 53 Those results suggested that the Z-isomers should exhibit different binding modes compared to the E-isomers.…”

Conformational studies of novel estrogen receptor ligands by 1D and 2D NMR spectroscopy and computational methods

“…Ł Correspondence to: Robert N. Hanson Recently, we showed that the placement of a substituent in the ortho or para position of (17˛,20Z)phenylvinylestradiol affected the conformational equilibrium of the 17˛side-chain. 4 In that study, (17˛,20Z)-(p-methoxyphenyl)vinylestradiol and (17˛,20Z)-(o-trifluoromethylphenyl)vinylestradiol were found to exist in similar conformational equilibria, which suggested they would likely occupy a similar receptor volume. These results were consistent with their similar RBA values of 20 and 23.…”