"2,3-Benzodiazepine (2,3-BDZ) compounds are a group of AMPA inhibitors and are drug candidates for treating neurological diseases involving receptor inhibit excessive AMPA receptor activity. We investigated the mechanism by which GluA2Qflip receptor channel opening is inhibited by two 2,3-BDZ derivatives, i.e.,1-(4-aminophenyl)-3,5-dihydro-7,8-ethylenedioxy-4H-2,3-benzodiazepin-4-one (2,3-BDZ-11-2) and its 1-(4-amino-3-chlorophenyl) analogue (2,3-BDZ-11-4). Both compounds have a 7,8-ethylenedioxy moiety instead of the 7,8-methylenedioxy feature present in the structure of GYKI 52466, the prototypic 2,3-BDZ compound. Using a laser-pulse photolysis approach with a time resolution of ∼60 μs and a rapid solution flow technique, we characterized the effect of the two compounds on the channel opening process of the homomeric GluA2Qflip receptor. We found that both 2,3-BDZ-11-2 and 2,3-BDZ-11-4 are noncompetitive inhibitors with specificity for the closed-channel conformation of the GluA2Qflip receptor. However, 2,3-BDZ-11-4 is ∼10-fold stronger, defined by its inhibition constant for the closed-channel conformation (i.e., KI = 2 μM), than 2,3-BDZ-11-2. From double-inhibitor experiments, we determined that both compounds bind to the same site, but this site is different from two other known, noncompetitive binding sites on the GluA2Qflip receptor previously reported. Our results provide both mechanistic clues to improve our understanding of AMPA receptor regulation and a structure−activity relationship for designing more potent 2,3-BDZ compounds with predictable properties for this new noncompetitive site.