Binding of 5H-dibenzo[b,e][1,4]diazepine and chiral 5H-dibenzo[a,d]cycloheptene analogues of clozapine to dopamine and serotonin receptors.

ABSTRACT

5H-Dibenzo[b,e][1,4]diazepine, dibenz[b,f]oxepin, and 5H-dibenzo[a,d]cycloheptene analogues of clozapine [8-chloro-11-(4-methylpiperazino)-5H- dibenzo[b,e][1,4]diazepine] were evaluated for their binding affinity to dopamine D-1, D-2, and D-4 and serotonin S-2A (5-HT2A), S-2C (5-HT2C) and S-3 (5-HT3) receptors. The diazepine analogues display selective binding to the dopamine D-4 and serotonin S-2A receptors similar to that of clozapine, but none has a dopamine D-4 selectivity (Ki for the dopamine D-2A receptor/Ki for the dopamine D-4 receptor) greater than that of clozapine. All of the oxepin analogues also show substantial binding to the dopamine D-4 and serotonin S-2A receptors with 10-(4-methylpiperazino)dibenz[b,f]oxepin having a dopamine D-4 selectivity greater than that of clozapine. Some of the 5H-dibenzo-[a,d]cycloheptene analogues also show strong binding to both the dopamine D-4 and serotonin S-2A receptors, 5-methyl-10-(4-methylpiperazino)-5H-dibenzo[a,d]cycloheptene having a dopamine D-4 selectivity of 7.8 as compared to 10 for clozapine but a serotonin S-2A selectivity (Ki for the dopamine D-2 receptor/Ki for the serotonin S-2A receptor) of 2.0 as compared to 28 for clozapine. The serotonin S-2A selectivity of 2-chloro-10-(4-methylpiperazino)-5H-dibenzo[a,d]-cycloheptene++ + is 200. As an extension of these studies, chiral 5-substitute 10-(1,2,3,6-tetrahydro-1-methyl-4-pyridinyl)-5H-dibenzo[a,d]cyclohept ene analogues show a substantial enantiospecificity toward dopamine and serotonin receptor subtypes, (R)-(-)-5-methyl compound having a 2-fold higher dopamine D-4 selectivity than its (S)-(+) enantiomer as the result of enhanced binding to the dopamine D-4 receptor rather than diminished binding to the dopamine D-2 receptor. (pRa,pSb)-(+)-5-(2-Propylidene)-10-(1,2,3,6-tetrahydro-1-met hyl- 4-pyridinyl)-5H-dibenzo[a,d]cycloheptene is 17 times more active in binding to the dopamine D-4 receptor than is its pSa,pRb enantiomer while being only 1.5 times more active in binding to the dopamine D-2 receptor.