ANALOGS OF 3-HYDROXY-1H-1-BENZAZEPINE-2,5-DIONE - STRUCTURE-ACTIVITY RELATIONSHIP AT N-METHYL-D-ASPARTATE RECEPTOR GLYCINE SITES

A series of aromatic and azepine ring-modified analogs of 3-hydroxy-1H -1-benzazepine-2,5-dione (HEAD) were synthesized and evaluated as anta gonists at NMDA receptor glycine sites. Aromatic ring-modified HBADs w ere generally prepared via a Schmidt reaction with substituted 2-metho xynaphthalene-1,4-diones followed by demethylation. Electrophilic arom atic substitution of benzazepine 3-methyl ethers gave 7-substituted an alogs. The preparation of multiply sub stituted 2-methoxynaphthalene-1 ,4-diones was effected via Diels-Alder methodology utilizing substitut ed butadienes with 2-methoxybenzoquinones followed by aromatization. S tructural modifications, such as elimination of the aromatic ring, rem oval of the 3-hydroxyl group, and transfer of the hydroxyl group from C-3 to C-4, were also studied. An initial evaluation of NMDA antagonis m was performed using a [H-3]MK801 binding assay. HBADs demonstrating NMDA antagonist activity as indicated by inhibition of[H-3]MK801 bindi ng were further evaluated employing a [H-3]-5,7-dichlorokynurenic acid (DCKA) glycine site binding assay. Selected HBADs were characterized for functional antagonism of NMDA and AMPA receptors using electrophys iological assays in Xenopus oocytes and cultured rat cortical neurons. Antagonist potency of HBADs showed good correlation between the diffe rent assay systems. HBADs substituted at the 8-position possessed the highest potency with the 8-methyl (5), 8-chloro (6), and 8-bromo (7) a nalogs being the most active. For HEAD 6, the IC50 in [H-3]-DCKA bindi ng assays was 0.013 mu M and the K-b values for antagonism of NMDA rec eptors in oocytes (NR1a/2C) and cortical neurons were 0.026 and 0.048 mu M, respectively. HBADs also antagonized AMPA-preferring non-NMDA re ceptors expressed in oocytes but at a lower potency than corresponding inhibition of NMDA receptors. HBADs demonstrating a high potency for NMDA glycine sites showed the highest steady-state selectivity index r elative to AMPA receptors. Substitution at the 6-, 7-, and 9-positions generally reduced or eliminated glycine site affinity. Moving the hyd roxyl group from C-3 to C-4 reduced receptor affinity, and potency was eliminated by the removal of the aromatic ring or the hydroxyl group. These data indicate that the HEAD series has specific structural requ irements for high receptor affinity. With the exception of substitutio n at C-8, modified HBADs generally have a lower affinity at NMDA recep tor glycine sites than the parent compound 3. Mouse maximum electrosho ck-induced seizure studies show that the three HBADs selected for test ing have in vivo potency with the 6,8-dimethyl analog (52) being the m ost potent (ED(50) = 3.9 mg/kg, iv).