Discovery of a series of pyrrolidine-based endothelin receptor antagonists with enhanced ET(A) receptor selectivity

C-3- and C-4-Substituted Bicyclic Coumarin Sulfamates as Potent Steroid Sulfatase Inhibitors

Synthetic routes to potent bicyclic nonsteroidal sulfamate-based active-site-directed inhibitors of the enzyme steroid sulfatase (STS), an emerging target in the treatment of postmenopausal hormone-dependent diseases, including breast cancer, are described. Sulfamate analogs 9-27 and 28-46 of the core in vivo active two-ring coumarin template, modified at the 4- and 3-positions, respectively, were synthesized to expand structure-activity relationships. α-Alkylacetoacetates were used to synthesize coumarin sulfamate derivatives with 3-position modifications, and the bicyclic ring of other parent coumarins was primarily constructed via the Pechmann synthesis of hydroxyl coumarins. Compounds were examined for STS inhibition in intact MCF-7 breast cancer cells and in placental microsomes. Low nanomolar potency STS inhibitors were achieved, and some were found to inhibit the enzyme in MCF-7 cells ca. 100-500 more potently than the parent 4-methylcoumarin-7-O-sulfamate 3, with the best compounds close in potency to the tricyclic clinical drug Irosustat. 3-Hexyl-4-methylcoumarin-7-O-sulfamate 29 and 3-benzyl-4-methylcoumarin-7-O-sulfamate 41 were particularly effective inhibitors with IC50 values of 0.68 and 1 nM in intact MCF-7 cells and 8 and 32 nM for placental microsomal STS, respectively. They were docked into the STS active site for comparison with estrone 3-O-sulfamate and Irosustat, showing their sulfamate group close to the catalytic hydrated formylglycine residue and their pendant group lying between the hydrophobic sidechains of L103, F178, and F488. Such highly potent STS inhibitors expand the structure-activity relationship for these coumarin sulfamate-based agents that possess therapeutic potential and may be worthy of further development.

2-[1'-(Benz-yloxy)spiro-[indane-1,2'-pyrrolidine]-5'-yl]aceto-nitrile

In the title compound, C₂₁H₂₂N₂O, the planes of the two six-membered rings make a dihedral angle of 89.51 (7)°. The pyrrolidine ring has a puckering amplitude q₂ = 0.418 (3) and a pseudo-rotation phase angle ϕ₂ = −166.8 (5), adopting a twist conformation (T). The other five-membered ring has a puckering amplitude q₂ = 0.247 (2) and a pseudo-rotation phase angle ϕ₂ = −173.7 (5), adopting an envelope conformation with the CH₂ atom adjacent to the C atom common with the pyrrolidine ring as the flap. In the crystal, mol­ecules are linked via C—H⋯N, enclosing R²₂(20) rings, forming chains propagating along [100]. The aceto­nitrile group is disordered over two positions and was refined with a fixed occupancy ratio of 0.56:0.44.

Synthesis, in vitro pharmacology and biodistribution studies of new PD 156707-derived ET(A) receptor radioligands

It is assumed that the regulation of cardiac endothelin (ET) receptor density is abnormal in heart diseases. From that perspective, an ET receptor radioligand is needed to assess ET receptor density in vivo. The nonpeptidyl ET(A) receptor antagonist PD 169390 was labelled with radioiodine to give a putative radioligand for SPECT. Labelling with [125I]iodide and [123I]iodide was accomplished with good to excellent radiochemical yields. The affinities of the nonradioactive reference and those of selected precursor compounds for ET(A) receptors were determined, using [125I]iodine labelled endothelin-1 with mouse ventricular membranes. All employed substances exhibited potent in vitro pharmacological characteristics with Ki values comparable to that of the lead compound PD 156707. Biodistribution studies and scintigraphic imaging experiments in mice, however, showed no significant uptake of the [123I] derivative in the heart.

Solid-phase synthesis of endothelin receptor antagonists

A new solid-phase synthesis for ET receptor antagonists suitable for automation is presented. A support bound 2-hydroxybutyric acid derivative was converted to the corresponding ether derivatives using 4-halo-2-methylsulfonylpyrimidines. Subsequent Suzuki coupling with various aryl boronic acids gave the desired antagonists in good yields and purities. Highly potent antagonists with excellent selectivity for ET(A) were obtained.

Molecular modeling and pharmacological analysis of species-related histamine H(3) receptor heterogeneity

Presynaptic histamine H(3) receptors (H(3)R) regulate neurotransmitter release in the central nervous system, suggesting an important role for H(3) ligands in human diseases such as cognitive disorders, sleep disturbances, epilepsy, or obesity. Drug development for many of these human diseases relies upon rodent-based models. Although there is significant sequence homology between the human and rat H(3)Rs, some compounds show distinct affinity profiles. To identify the amino acids responsible for these species disparities, various mutant receptors were generated and their pharmacology studied. The N-terminal portion was shown to determine the species differences in ligand binding since a chimeric H(3)R containing N-terminal human and C-terminal rat receptor sequences exhibited similar pharmacology to the human receptor. Sequence analysis and molecular modeling studies suggested key amino acids at positions 119 and 122 in transmembrane region 3 play important roles in ligand recognition. Mutant receptors changing amino acids 119 or 122 of the human receptor to those in the rat improved ligand binding affinities and functional potencies of antagonist ligands, confirming the significant role that these amino acids play in species-related pharmacological differences. A model has been developed to elucidate the ligand receptor interactions for H(3)Rs, and pharmacological aspects of this model are described.

Peptoids as endothelin receptor antagonists

A series of new peptoids as endothelin receptor antagonists has been synthesized. Screening them for their ability to bind with endothelin receptors (ET(A) and ET(B)) competitively in the presence of (125I) endothelin led to the discovery of compounds as possible leads with IC50s in the low micromolar concentrations.