Further evaluation of the tropane analogs of haloperidol

Previous work from our labs has indicated that a tropane analog of haloperidol with potent D₂ binding but designed to avoid the formation of MPP⁺-like metabolites, such as 4-(4-chlorophenyl)-1-(4-(4-fluorophenyl)-4-oxobutyl)pyridin-1-ium (BCPP⁺) still produced catalepsy, suggesting a strong role for the D₂ receptor in the production of catalepsy in rats, and hence EPS in humans. This study tested the hypothesis that further modifications of the tropane analog to produce compounds with less potent binding to the D₂ receptor than haloperidol, would produce less catalepsy. These tests have now revealed that while haloperidol produced maximum catalepsy, these compounds produced moderate to low levels of catalepsy. Compound 9, with the least binding affinity to the D₂R, produced the least catalepsy and highest Minimum Adverse Effective Dose (MAED) of the analogs tested regardless of their affinities at other receptors including the 5-HT_1AR. These observations support the hypothesis that moderation of the D₂ binding of the tropane analogs could reduce catalepsy potential in rats and consequently EPS in man.