4-Chloro Kynurenine-13C2,15N

7-Cl-kynurenic acid (7-Cl-KYNA) is a potent, selective antagonist of the NMDA/glycine receptor but penetrates poorly through the blood-brain barrier.  Its prodrug, L-4-Cl-kynurenine (4-Cl-KYN), readily enters the brain from the circulation and provides antiexcitotoxic neuroprotection after systemic application.