Macrocyclic Retinoic Acid Receptor-Related Orphan Receptor C2 Inverse Agonists

Macrocyclic retinoic acid receptor-related orphan receptor C2 (RORC2) inverse agonists have been designed with favorable properties for topical administration. Inspired by the unanticipated bound conformation of an acyclic sulfonamide-based RORC2 ligand from cocrystal structure analysis, macrocyclic linker connections between the halves of the molecule were explored. Further optimization of analogues was accomplished to maximize potency and refine physiochemical properties (MW, lipophilicity) best suited for topical application. Compound 14 demonstrated potent inhibition of interleukin-17A (IL-17A) production by human Th17 cells and in vitro permeation through healthy human skin achieving high total compound concentration in both skin epidermis and dermis layers.

Discovery and Optimization of a Series of Sulfonamide Inverse Agonists for the Retinoic Acid Receptor-Related Orphan Receptor-α

BACKGROUND

Despite a massive industry endeavor to develop RORγ-modulators for autoimmune disorders, there has been no indication of efforts to target the close family member RORα for similar indications. This may be due to the misconception that RORα is redundant to RORγ, or the inherent difficulty in cultivating tractable starting points for RORα. RORα-selective modulators would be useful tools to interrogate the biology of this understudied orphan nuclear receptor.

OBJECTIVE

The goal of this research effort was to identify and optimize synthetic ligands for RORα starting from the known LXR agonist T0901317.

METHODS

Fourty-five analogs of the sulfonamide lead (1) were synthesized and evaluated for their ability to suppress the transcriptional activity of RORα, RORγ, and LXRα in cell-based assays. Analogs were characterized by 1H-NMR, 13C-NMR, and LC-MS analysis. The pharmacokinetic profile of the most selective RORα inverse agonist was evaluated in rats with intraperitoneal (i.p.) and per oral (p.o.)dosing.

RESULTS

Structure-activity relationship studies led to potent dual RORα/RORγ inverse agonists as well as RORα-selective inverse agonists (20, 28). LXR activity could be reduced by removing the sulfonamide nitrogen substituent. Attempts to improve the potency of these selective leads by varying substitution patterns throughout the molecule proved challenging.

CONCLUSION

The synthetic RORα-selective inverse agonists identified (20, 28) can be utilized as chemical tools to probe the function of RORα in vitro and in vivo.

Modular radical cross-coupling with sulfones enables access to sp3-rich (fluoro)alkylated scaffolds

Cross-coupling chemistry is widely applied to carbon-carbon bond formation in the synthesis of medicines, agrochemicals, and other functional materials. Recently, single-electron-induced variants of this reaction class have proven particularly useful in the formation of C(sp²)-C(sp³) linkages, although certain compound classes have remained a challenge. Here, we report the use of sulfones to activate the alkyl coupling partner in nickel-catalyzed radical cross-coupling with aryl zinc reagents. This method's tolerance of fluoroalkyl substituents proved particularly advantageous for the streamlined preparation of pharmaceutically oriented fluorinated scaffolds that previously required multiple steps, toxic reagents, and nonmodular retrosynthetic blueprints. Five specific sulfone reagents facilitate the rapid assembly of a vast set of compounds, many of which contain challenging fluorination patterns.

Antiproliferation activity of a small molecule repressor of liver receptor homolog 1

The orphan nuclear receptor liver receptor homolog 1 (LRH-1; NR5A2) is a potent regulator of cholesterol metabolism and bile acid homeostasis. Recently, LRH-1 has been shown to play an important role in intestinal inflammation and in the progression of estrogen receptor positive and negative breast cancers and pancreatic cancer. Structural studies have revealed that LRH-1 can bind phospholipids and the dietary phospholipid dilauroylphosphatidylcholine activates LRH-1 activity in rodents. Here we characterize the activity of a novel synthetic nonphospholipid small molecule repressor of LRH-1, SR1848 (6-[4-(3-chlorophenyl)piperazin-1-yl]-3-cyclohexyl-1H-pyrimidine-2,4-dione). In cotransfection studies, SR1848 reduced LRH-1-dependent expression of a reporter gene and in cells that endogenously express LRH-1 dose dependently reduced the expression of cyclin-D1 and -E1, resulting in inhibition of cell proliferation. The cellular effects of SR1848 treatment are recapitulated after transfection of cells with small-interfering RNA targeting LRH-1. Immunocytochemistry analysis shows that SR1848 induces rapid translocation of nuclear LRH-1 to the cytoplasm. Combined, these results suggest that SR1848 is a functional repressor of LRH-1 that impacts expression of genes involved in proliferation in LRH-1-expressing cancers. Thus, SR1848 represents a novel chemical scaffold for the development of therapies targeting malignancies driven by LRH-1.

Generation of stereochemically defined tetrasubstituted enolborinates by 1,4-hydroboration of α,β-unsaturated morpholine carboxamides with (diisopinocampheyl)borane

On all fours: The title reaction with (Ipc)2 BH provides tetrasubstituted enolborinates which undergo aldol reactions with aldehydes to form products with all-carbon quaternary centers with exceptional diastereo- and enantioselectivity. A change to the substitution pattern of the starting amide leads to either diastereomer of the α-methyl-α-ethyl-β-hydroxy carboxamide (1 or 2).

(Diisopinocampheyl)borane-mediated reductive aldol reactions of acrylate esters: enantioselective synthesis of anti-aldols

The (diisopinocampheyl)borane promoted reductive aldol reaction of acrylate esters 4 is described. Isomerization of the kinetically formed Z(O)-enolborinate 5Z to the thermodynamic E(O)-enolborinate 5E via 1,3-boratropic shifts, followed by treatment with representative achiral aldehydes, leads to anti-α-methyl-β-hydroxy esters 9 or 10 with excellent diastereo- (up to ≥20:1 dr) and enantioselectivity (up to 87% ee). The results of double asymmetric reactions of 5E with several chiral aldehydes are also presented.

Enantio- and diastereoselective synthesis of N-acetyl dihydrotetrafibricin methyl ester

A highly diastereoselective synthesis of N-acetyl dihydrotetrafibricin methyl ester (34) is described. The synthesis features three enantioselective double allylboration reactions and an intramolecular hydrosilylation/Fleming-Tamao oxidation sequence to establish seven of the hydroxy-bearing stereocenters of 34. Especially noteworthy is the fragment-assembly double allyboration reaction of 2 and 7 using reagent 3, which provides the advanced intermediate 6 with >20:1 diastereoselectivity.

Development of a Double Allylboration Reagent Targeting 1,5-syn-(E)-Diols: Application to the Synthesis of the C(23)-C(40) Fragment of Tetrafibricin

Interest in the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin prompted us to develop a new method for the synthesis of 1,5-syn-(E)-diols. Toward this end, the kinetically controlled hydroboration of allenes 6, 33, ent-39, 42 and 45 with the Soderquist borane 25R were studied. Tetrabutylammonium allenyltrifluoroborate 45 gave superior results and was utilized in a double allylboration sequence with two different aldehydes to provide the targeted 1,5-syn-(E)-diols in generally high yields (72-98%), and with high enantioselectivity (>95% e.e.), diastereoselectivity (d.r. >20:1), and (E)/(Z) selectivity (>20:1). This new method was applied to the synthesis of the C(23)-C(40) fragment 2 of tetrafibricin.

Suppression of TH17 differentiation and autoimmunity by a synthetic ROR ligand

T helper cells that produce Interleukin-17 (IL-17) (T_H17 cells) are a recently identified CD4⁺ T-cell subset with characterized pathological roles in autoimmune diseases^1–3. The nuclear receptors retinoic acid receptor-related orphan receptors α and γt (RORα and RORγt) have indispensible roles in the development of this cell type^4–7. Here we present a first-in-class, high-affinity synthetic ligand, SR1001, specific to both RORα and RORγt that inhibits T_H17 cell differentiation and function. SR1001 binds specifically to the ligand binding domains (LBDs) of RORα and RORγt inducing a conformational change within the LBD that encompasses repositioning of helix 12 leading to diminished affinity for coactivators and increased affinity for corepressors resulting in suppression of the receptors transcriptional activity. SR1001 inhibited the development of murine T_H17 cells as demonstrated by inhibition of IL-17A gene expression and protein production. Additionally, SR1001 inhibited the expression of cytokines when added to differentiated murine or human T_H17 cells. Finally, SR1001 effectively suppressed the clinical severity of autoimmune disease in mice. Thus, our data demonstrates the feasibility of targeting the orphan receptors RORα and RORγt to specifically inhibit T_H17 cell differentiation and function and indicates that this novel class of compound has potential utility in the treatment of autoimmune diseases.

Enantio- and diastereoselective synthesis of (E)-1,5-syn-diols: application to the synthesis of the C(23)-C(40) fragment of tetrafibricin

A highly stereoselective synthesis of (E)-1,5-syn-diols 6 is described. The kinetically controlled hydroboration of allenyltrifluoroborate 8 with Soderquist borane 2 provides the (Z)-allylic trifluoroborate 9, which undergoes sequential allylboration with two different aldehydes to provide (E)-1,5-syn-diols 6 in 72-98% yields with >95% ee and >20:1 dr. Application of this method to the synthesis of the tetrafibricin C(23)-C(40) fragment 19 is described.

Identification of SR3335 (ML-176): a synthetic RORα selective inverse agonist

Several nuclear receptors (NRs) are still character-ized as orphan receptors because ligands have not yet been identified for these proteins. The retinoic acid receptor-related receptors (RORs) have no well-defined physiological ligands. Here, we describe the identification of a selective RORα synthetic ligand, SR3335 (ML-176). SR3335 directly binds to RORα, but not other RORs, and functions as a selective partial inverse agonist of RORα in cell-based assays. Furthermore, SR3335 suppresses the expression of endogenous RORα target genes in HepG2 involved in hepatic gluconeogenesis including glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. Pharmacokinetic studies indicate that SR3335 displays reasonable exposure following an ip injection into mice. We assess the ability of SR3335 to suppress gluconeogenesis in vivo using a diet-induced obesity (DIO) mouse model where the mice where treated with 15 mg/kg b.i.d., ip for 6 days followed by a pyruvate tolerance test. SR3335-treated mice displayed lower plasma glucose levels following the pyruvate challenge consistent with suppression of gluconeogenesis. Thus, we have identified the first selective synthetic RORα inverse agonist, and this compound can be utilized as a chemical tool to probe the function of this receptor both in vitro and in vivo. Additionally, our data suggests that RORα inverse agonists may hold utility for suppression of elevated hepatic glucose production in type 2 diabetics.

Identification of SR1078, a synthetic agonist for the orphan nuclear receptors RORα and RORγ

The retinoic acid receptor-related receptors (RORs) are members of the nuclear receptor (NR) superfamily of transcription factors. Several NRs are still characterized as orphan receptors because ligands have not yet been identified for these proteins. Here, we describe the identification of a synthetic RORα/RORγ ligand, SR1078. SR1078 modulates the conformation of RORγ in a biochemical assay and activates RORα and RORγ driven transcription. Furthermore, SR1078 stimulates expression of endogenous ROR target genes in HepG2 cells that express both RORα and RORγ. Pharmacokinetic studies indicate that SR1078 displays reasonable exposure following injection into mice, and consistent with SR1078 functioning as a RORα/RORγ agonist, expression of two ROR target genes, glucose-6-phosphatase and fibroblast growth factor 21, were stimulated in the liver. Thus, we have identified the first synthetic RORα/γ agonist, and this compound can be utilized as a chemical tool to probe the function of these receptors both in vitro and in vivo.

Enhancement of 5-aminopenta-2,4-dienals electrophilicity via activation by O,N-bistrifluoroacetylation. application to an N-acyl Pictet-Spengler reaction

Aminopentadienals resulting from the condensation of tryptamine or homoveratrylamine with glutaconaldehydes were treated with trifluoroacetic anhydride, allowing the formation of tetrahydro-beta-carbolines and tetrahydroisoquinolines bearing an enal function. In this N-acyl Pictet-Spengler reaction the electrophilicity of the aminopentadienals was dramatically increased by O,N-bistrifluoroacetylation. Recovery of the nitrogen nucleophilicity was achieved using a reductive process, and the heterocyclic amines were converted into aminonitriles by a Strecker reaction in the presence of butanal. Cyclization, by intramolecular Michael addition of the in situ generated enamines onto the enal moiety, was achieved in the presence of zinc triflate and involved cyanide ion trapping. In this manner, compounds related to protoemetine and dihydrocorynantheal were obtained, and a reduction step led to a short synthesis of (+/-)-protoemetinol.

α,α‘-Annulation of 2,6-Prenyl-Substituted Cyclohexanone Derivatives with Malonyl Chloride: Application to a Short Synthesis of (±)-Clusianone. Formation and Rearrangement of a Biogenetic-Like Intermediate

Conditions were found for the successful Effenberger alpha,alpha'-annulation of 3,3-dimethyl-2,4,6-triprenyl cyclohexanone silyl enol ethers with malonyl chloride to give the corresponding bicyclo[3.3.1]nonane-trione in 35% yield, this result allowing a short synthesis of (+/-)-clusianone. An isomeric rearranged bicyclo[3.3.1]nonane-trione was also isolated in 25% yield, and changing the Lewis acid resulted in formation of a lavandulyl-substituted phloroglucinol derivative in 38% yield. The mechanism of formation of these two last products mimics the biogenetic pathway to PPAPs. [reaction: see text].