Members of the series of title compounds were tested for potential antipsychotic activity in relevant receptor binding assays and behavioral screens. Structure-activity relationships within the series are discussed. Compound 24 (BMY 13859-1), a (1,2-benzisothiazol-3-yl)piperazine derivative, was selected for further study because of its potent and selective profile in primary CNS tests. It was active in the Sidman avoidance paradigm and blocked amphetamine-induced stereotyped behavior in dogs for up to 7 h. The compound's lack of typical neuroleptic-like effects in the rat catalepsy test and its failure to produce dopamine receptor supersensitivity following chronic administration indicate that it should not cause the movement disorders commonly associated with antipsychotic therapy. Although 24 has potent affinity for dopaminergic binding sites, its even greater affinity for serotonin receptors suggests that a serotonergic component may be relevant to its atypical profile. Compound 24 is currently undergoing clinical evaluation in schizophrenic patients.

A series of novel 3,4-dihydro-4-oxothieno[2,3-d]pyrimidine-2-carboxylic acid derivatives has been prepared and tested for antiallergenic activity. Members of the series, including both carboxylic acid salts and esters, have been found to exhibit oral activity in the rat passive cutaneous anaphylaxis (PCA) test. Activity is optimized by H or CH3 substitution at the 5 position and lower alkyl groups at the 6 position. Ethyl 6-ethyl-3,4-dihydro-4-oxothieno-[2,3-d]pyrimidine-2-carboxylate and 3,4-dihydro-5-methyl-6-(2-methylpropyl)-4-oxothieno[2,3-d]pyrimidine-2-carboxylic acid dipotassium salt were the most potent of the esters and salts, respectively. Such compounds have been shown to have a duration of action of up to 4 h in the PCA test and to inhibit both histamine release from rat peritoneal mast cells in vitro and allergen-induced bronchospasm in the rat lung.

A series of 1-(pyrimidin-2-yl)piperazine derivatives were prepared and evaluated in receptor binding assays and in in vivo behavioral paradigms as potential atypical antipsychotic agents. Compound 16 (BMS 181100 (formerly BMY 14802)) emerged as the lead compound from within the series on the basis of its good activity and duration of action in the inhibition of both conditioned avoidance responding and apomorphine-induced stereotopy in the rat. Compound 16 not only failed to induce catalepsy in the rat but was quite effective in reversing the cataleptic effect of neuroleptic agents, thus indicating a low propensity for causing extrapyramidal side effects. In comparison to reference antipsychotic agents, 16 appeared to be less sedating and was relatively weaker in causing muscle incoordination. The compound was essentially inactive in binding to dopamine D2 receptors and its chronic administration to rats did not result in dopamine receptor supersensitivity. It exhibited modest to weak affinity for 5-HT1A and alpha 1 receptors but was found to be a fairly potent ligand for sigma binding sites (IC50 vs (+)-[3H]-3-PPP = 112 nM). Although the resolved enantiomers of racemic 16 did not show dramatic differences from racemate or from each other in most tests, the R(+) enantiomer was up to 11-fold more potent than its antipode in binding to sigma sites. Several studies have indicated that 16 may be a limbic-selective agent which may modulate dopaminergic activity by an indirect mechanism. The compound has been selected for clinical evaluation in the treatment of psychosis.

A series of analogues of buspirone was synthesized in which modifications were made in the aryl moiety, alkylene chain length, and cyclic imide portion of the molecule. These compounds were tested in vitro for their binding affinities to rat brain membrane sites labeled by either the dopamine antagonist [3H]spiperone or the alpha 1-adrenergic antagonist [3H]WB-4101. Compounds were also tested in vivo for tranquilizing properties and induction of catalepsy. Potency at the [3H]spiperone binding site was affected by alkylene chain length and imide portion composition. Nonortho substituents on the aryl moiety had little effect on [3H]spiperone binding affinity. Structure-activity relationships of ortho substituents demonstrated only modest correlations between the receptor binding data and physical parameters of the substituents. The complex nature of the drug-receptor interactions may be understood in terms of the fit of buspirone to a hypothetical model of the dopamine receptor.

Putative oxidative metabolites of the lead antipsychotic agent tiospirone (1) were synthesized to assist in the identification of the authentic metabolic products found in human urine samples. Thus far, six authentic metabolites have been correlated to the synthetic species. The putative metabolites were further examined in vitro to assess their central nervous system therapeutic potential. SAR analysis of these derivatives indicates that hydroxyl substitution, particularly in the azaspirodecanedione region of the molecule, diminishes the dopamine D-2 affinity of the species without significantly altering the serotonin type-1A and type-2 interactions. In addition, an increase in alpha 1-adrenergic affinity appears to be linked to the attenuation of effects at the dopamine receptors. The biological profile of the 6-hydroxytiospirone metabolite 42 was exemplary in these respects and the in vivo actions of this compound suggest potent antipsychotic potential with a minimal liability for extrapyramidal side effects (EPS). While compound 42 has been unambiguously characterized as an actual human metabolite of tiospirone, the role of 42 in the observed antipsychotic activity of the parent drug, if any, has not yet been determined.