Isoxazolopyrimidines as Novel ΔF508-CFTR Correctors

Abstract

Using a cell-based high-throughput screen, we identified isoxazolo[5,4-d]pyrimidines as novel small-molecule correctors of the cystic fibrosis mutant protein ΔF508-CFTR. 22 Isoxazolo[5,4-d]pyrimidine analogues were synthesized and tested. Synthesis of the key intermediate, 5-amino-3-arylisoxazole-4-carboxamide, was accomplished by nitrile oxide cycloaddition to (2-amino-1-cyano-2-oxoethyl)sodium. Formation of 3-arylisoxazolo-[5,4-d]pyrimidin-4(5H)-one and chlorination gave 4-chloro-3-arylisoxazolo[5,4-d]pyrimidine. Finally, functionalization at C-4 of the pyrimidine ring by nucleophilic substitution gave the targeted isoxazolo[5,4-d]pyrimidines. Six of the reported analogues had low micromolar potency for increasing halide transport in ΔF508-CFTR cells.

Keywords: corrector; cystic fibrosis; isoxazolopyrimidine; ΔF508-CFTR.

Figure 1

N-Methyl and pyridyl analogues of 7

Scheme 1

Reagents: (a) NH₂OH·HCl, H₂O–EtOH–THF, NaOAc, 66–100%; (b) NCS, DMF–MeCl, Et₃N, pyridine (cat.), 60–95%; (c) i) 2-cyanoacetamide, NaOEt, EtOH, ii) 3, EtOH, 35–89%; (d) triethyl orthoformate, Ac₂O, reflux, 2.5 h, 48–75%; (e) POCl₃ (0.83 equiv), N, N-dimethylaniline (2 equiv), Et₃N·HCl (2 equiv), MeCN, reflux under N₂, sealed tube, 2.5 h, 83–92%; (f) 2,3-dimethylaniline, i-PrOH, HCl (gas), 30–76%.