Scaffold Hopping from Amodiaquine to Novel Nurr1 Agonist Chemotypes via Microscale Analogue Libraries

Abstract

Several lines of evidence suggest the ligand-sensing transcription factor Nurr1 as a promising target to treat neurodegenerative diseases. Nurr1 modulators to validate and exploit this therapeutic potential are rare, however. To identify novel Nurr1 agonist chemotypes, we have employed the Nurr1 activator amodiaquine as template for microscale analogue library synthesis. The first set of analogues was based on the 7-chloroquiolin-4-amine core fragment of amodiaquine and revealed superior N-substituents compared to diethylaminomethylphenol contained in the template. A second library of analogues was subsequently prepared to replace the chloroquinolineamine scaffold. The two sets of analogues enabled a full scaffold hop from amodiaquine to a novel Nurr1 agonist sharing no structural features with the lead but comprising superior potency on Nurr1. Additionally, pharmacophore modeling based on the entire set of active and inactive analogues suggested key features for Nurr1 agonists.

Keywords: NR4A2; neurodegeneration; nuclear receptor-related 1; pharmacophore model; transcription factor.

Scheme 1

Nurr1 agonists.

Figure 1

Schematic workflow of analogue library synthesis and in vitro testing. Created with BioRender.com.

Scheme 2

Preparation of microscale analogue libraries. Reagents & Conditions: (a) NaBH(OAc)₃, HOAc, CH₂Cl₂, r.t., 24 h; (b) 4‐DMAP, CH₂Cl₂, r.t., 24 h.

Scheme 3

Batch synthesis of Nurr1 agonists 3 j, 4, 4 e and 5. Reagents & Conditions: (a) EDC⋅HCl, 4‐DMAP, CHCl₃/DMF, reflux, 24 h, 65–86 %; (b) LiAlH₄, THF, 0 °C–r.t., 24 h, 32 %; (c) i) LiAlH₄, THF, 0 °C, 5 min.; ii) MsCl, CH₂Cl₂/TEA, r.t., 1 h; iii) 6, toluene, reflux, 48 h, 11 %.

Figure 2

Library A: (a) Chemical structures of library A compounds and (b) single point screening data of crude library A at ∼30 μM. Data are the mean±SD, n=3. (c) Library product 3 j (purified compound) diminished Nurr1 homodimerization in an HTRF assay. Data are the mean±SD, N=3.

Figure 3

Library B: (a) Chemical structures of library B compounds and (b) single point screening data of crude library B at ∼3 μM. Data are the mean±SD, n=3.

Figure 4

In vitro profiling of Nurr1 agonist 4 e. (a) 4 e activated full‐length Nurr1 in reporter gene assays for the human Nurr1 response elements NBRE (Nurr1 monomer), NurRE (Nurr1 homodimer) and DR5 (Nurr1:RXR heterodimer). Nurr1 and RXR (for DR5) were overexpressed. Data are the mean±SD, n=3. (b) 4 e diminished Nurr1 homodimerization in an HTRF assay. Data are the mean±SD, N=3.

Figure 5

Pharmacophore model derived from Nurr1 activator AQ and analogues 3 a–3 n, 4, 4 a–4 u and 5. Pharmacophore features are color‐coded with hydrophobic/aromatic features in green, excluded volume in grey, H‐bond acceptors in cyan, H‐bond donors in purple, and the centroid projection along the π‐system plane normal in orange.