Design, synthesis and biological evaluation of 4-aminoquinoline derivatives as receptor-interacting protein kinase 2 (RIPK2) inhibitors

Abstract

Receptor-interacting protein kinase 2 (RIPK2) is an essential protein kinase mediating signal transduction by NOD1 and NOD2, which play an important role in regulating immune signalling. In this study, we designed and synthesised a novel series of 4-aminoquinoline-based derivatives as RIPK2 inhibitors. In vitro, compound 14 exhibited high affinity (IC₅₀ = 5.1 ± 1.6 nM) and excellent selectivity to RIPK2 showing in a dendrogram view of the human kinome phylogenetic tree. Bearing favourable lipophilicity and eligible lipophilic ligand efficiency (LipE), compound 14 was selected to investigate cellular anti-inflammatory effect and was identified as a potent inhibitor to reduce the secretion of MDP-induced TNF-α with a dose-dependent manner. Moreover, compound 14 showed moderate stability in human liver microsome. Given these promising results, compound 14 could serve as a favourable inhibitor of RIPK2 for further physiological and biochemical research so as to be used in therapeutic treatment.

Keywords: NOD; RIPK2 inhibitor; immunity; inflammation.

Figure 1.

Representative inhibitors of RIPK2.

Scheme 1.

Synthesis of 4-aminoquinoline-based derivatives. Reagents and conditions: (a) 6-bromo-4-chloroquinoline, amines, tert-butanol, 80 °C, 4 h; (b) boronic acids or boronic esters, Pd(PPh₃)₄, Na₂CO₃, H₂O, 1,4-dioxane, 80 °C, 8 h; (c) 2-pyridineboronic acid, Pd(OAc)₂, DPPF, Cs₂CO₃, CuCl, DMF, 80 °C, 12 h; (d) 6-bromo-4-chloroquinoline, amines, NaH, DMF, 0–40 °C.

Figure 2.

Docking study on compound 14 bound within the ATP site of RIPK2 (PDB ID: 6RNA).

Figure 3.

The effect of indicated compounds on the secretion of classic proinflammatory cytokine TNF-α in MDP-induced Raw264.7. TNF-α secretion in the supernatant of Raw264.7 cells from controls without stimulated, controls stimulated and compounds treated under stimulated conditions. The concentrations are presented as the mean ± SD. ^###p < 0.001 vs non-stimulated controls group, *p < 0.05, **p < 0.01, ***p < 0.001 vs stimulated controls group, in multivariate analysis.

Figure 4.

Compound 14 selectivity is represented in a dendrogram view of the human kinome phylogenetic tree. Red: >90% inhibition (5 kinase). Orange: 50 − 90% inhibition (3 kinases). Green: <50% inhibition. RIP2 kinase (red) inhibited by 97%.