Structure-activity relationship study of pyridazine derivatives as glutamate transporter EAAT2 activators

Abstract

Excitatory amino acid transporter 2 (EAAT2) is the major glutamate transporter and functions to remove glutamate from synapses. A thiopyridazine derivative has been found to increase EAAT2 protein levels in astrocytes. A structure-activity relationship study revealed that several components of the molecule were required for activity, such as the thioether and pyridazine. Modification of the benzylthioether resulted in several derivatives (7-13, 7-15 and 7-17) that enhanced EAAT2 levels by >6-fold at concentrations < 5 μM after 24h. In addition, one of the derivatives (7-22) enhanced EAAT2 levels 3.5-3.9-fold after 24h with an EC(50) of 0.5 μM.

Scheme 1

Reagents and conditions: (a) K₂CO₃, H₂O; (b) NH₂NH₂, AcOH, 100 °C (20%); (c) P₂S₅, pyridine, 120 °C (80%); (d) R²Br, K₂CO₃, DMF (90%); (e) MCPBA, CH₂Cl₂ (80%).

Scheme 2

Reagents and conditions: (a) Pd₂(dba)₃, XPhos, Cu(OAc)₂, K₂CO₃, DMF/i-PrOH (4/1), 100 °C; (b) H₂NR, ethanol, 85 °C (90%).

Scheme 3

Reagents and conditions: (a) Pd(PPh₃)₄, Na₂CO₃, CH₃CN/H₂O (1/1), 75 °C, 4-benzylthiophenylboronic acid (54%); (b) Pd(PPh₃)₄, Na₂CO₃, CH₃CN/H₂O (1/1), 75 °C, 6-hydroxypyridine-3-boronic acid pinacol ester (70%); (c) P₂S₅, pyridine, 120 °C (71%); (d) 2-methylbenzyl bromide, K₂CO₃, DMF (76%).