6,7-Dichloro-3-hydroxy-2-quinoxalinecarboxylic acid is a relatively potent antagonist at NMDA and kainate receptors.

The 6,7-dichloro derivative of 3-hydroxy-2-quinoxalinecarboxylic acid (diCl-HQC) is a relatively potent antagonist at the two excitatory amino acid receptor subtypes activated by N-methyl-D-aspartate (NMDA) and kainic acid. It antagonizes NMDA-induced excitation in the frog spinal cord (pA2 5.8), i.e. with a potency similar to D-2-amino-7-phosphonoheptanoate (D-AP-7). It also antagonizes NMDA-induced sodium efflux from rat brain slices (pA2 5.6). The compound inhibits kainic acid-induced sodium efflux from rat brain slices with a pA2 of 5.4 and it inhibits [3H]kainic acid binding to rat brain membranes with a pKi of 5.4. DiCl-HQC is only weakly active at the quisqualate receptor. This spectrum of activities may make this compound a useful tool to investigate the pharmacology of excitatory amino acid receptors.