– GR231118 TFA, a neuropeptide Y C-terminus analogue, acts as a potent, competitive, and relatively selective antagonist at the human neuropeptide YY receptor, exhibiting a pKi of 10.4. It serves as a strong agonist at the human neuropeptide YY4 receptor with a pEC50 of 8.6 and a pKi of 9.6, while demonstrating weak agonistic activity at both human and rat neuropeptide YY2 and YY5 receptors. Additionally, this compound shows high affinity for the mouse neuropeptide YY6 receptor, with a pKi value of 8.8 [1].