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Arecoline, arecaidine, and a series of derivatives, differing by the presence or absence of methyl groups at positions on the periphery of the molecule, were prepared, and their binding to muscarinic acetylcholine receptors was tested. On the basis of this study, muscarinic agonism for arecoline series is governed by strict structure-activity relationships, as previously observed for other agonist series. Only minor changes in nitrogen substitution were tolerated in the present series of arecoline derivatives.

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A series of N-phenyl-N'-pyridinylureas was examined for anticonvulsant activity. Extensive structure/activity investigations revealed optimal activity in the N-(2,6-disubstituted-phenyl)-N'-(4-pyridinyl)urea series, with 37 exhibiting the best overall anticonvulsant profile. Compound 37 was effective against seizures induced by maximal electroshock but did not protect mice from clonic seizures produced by the convulsant pentylenetetrazol. The overall pharmacological profile suggests that 37 would be of therapeutic use in the treatment of generalized tonic-clonic and partial seizures. Compound 37 was selected for Phase 1 clinical trials.

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The anticonvulsant activity of a series of 3-phenoxypyridine 1-oxides is described. An investigation carried out to optimize the activity/side effect ratio provided 4-methyl-3-phenoxypyridine 1-oxide, 3, as the derivative of choice. Overall, 3 has a pharmacological profile that is very similar to phenytoin. It exhibited significant anticonvulsant activity at doses that did not produce ataxia or sedation but caused increased spontaneous behavioral activity not seen with most anticonvulsants. The short duration of pharmacological effect of 3 was attributed to metabolic hydroxylation at the C-4 pyridine methyl group; however, structural modifications designed to inhibit this metabolic pathway were unsuccessful.

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The synthesis of a series of 1H-imidazo[1,2-c]pyrazolo[3,4-e]pyrimidines is reported along with the effects of these compounds in preclinical tests for antipsychotic activity. Certain of these compounds displayed antipsychotic-like effects in conditioned avoidance tests, but unlike currently used antipsychotic drugs, they did not have affinity for brain dopamine receptors. These compounds also did not cause dystonias predictive of extrapyramidal side effects in monkeys at doses that produced behavioral effects. On the basis of this unique biological profile, a member of this series 7,8-dihydro-8-ethyl-1,3,5-trimethyl-1H-imidao[1,2-c]pyrazol[3,4-e] pyrimidine (19, CI-943), has been selected for clinical evaluation as an antipsychotic agent.

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The anticonvulsant effect of a series of 6-alkoxy-N,N-disubstituted-2-pyridinamines is described. An investigation was carried out to optimize the activity/side-effect ratio in this series of compounds. The most desirable profile was seen with 1-[6-(2-methylpropoxy)-2-pyridinyl]piperazine, 6, and this compound was selected for a more complete pharmacological evaluation. Overall, 6 has a pharmacological profile that is very similar to that of diphenylhydantoin (phenytoin). While nearly equipotent to phenytoin, animal studies suggest a fairly short duration of action. In addition, 6 exhibited some troublesome side effects including central nervous system depression and hypothermia.

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A series of dihydro-1H-pyrrolizine-3,5(2H,6H)-diones were synthesized and evaluated for their ability to reverse electroconvulsive shock (ECS) induced amnesia in mice. Among the structure-activity relationships explored were the effects of ring size, the presence of heteroatoms (sulfur) in the ring system, and the introduction of alkyl substituents. The optimal ring size for the bicyclic system was 5.5 with dihydro-1H-pyrrolizine-3,5(2H,6H)-dione (3), although some activity was present in the corresponding 5.6 [hexahydro-3,5-indolizinedione (7)] and 6.6 [tetrahydro-2H-quinolizine-4,6(3H,7H)-dione (9)] analogues. Replacement of the C-1 carbon atom in compound 3 with a sulfur [dihydropyrrolo[2,1-b]thiazole-3,5(2H,6H)-dione (10)] abolished activity, and the introduction of methyl groups resulted in poorer biological profiles except when the substitution was made at the 7a position [dihydro-7a-methyl-1H-pyrrolizine-3,5(2H,6H)-dione (4)]. In several instances, hydrolysis of the parent bicyclic compound was carried out to furnish the corresponding lactam acids, which were further derivatized. Several exhibited interesting activity, especially the 5-oxo-2-pyrrolidinepropanoic acid derivatives such as 5-oxo-2-pyrrolidinepropanoic acid (12), 5-oxo-2-pyrrolidinepropanoic acid phenylmethyl ester (17), 5-oxo-2-pyrrolidinepropanoic acid (3-chlorophenyl)methyl ester (20), N-4-pyridyl-5-oxo-2-pyrrolidinepropanoic acid amide (25), and N-(2,6-dimethylphenyl)-5-oxo-2-pyrrolidinepropanoic acid amide (27). Compound 3 (CI-911; rolziracetam) was also observed to improve performance on a delayed-response task in aged rhesus monkeys and was selected for evaluation in cognitively impaired human subjects on the basis of its biological profile and a wide margin of safety in animals.

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Competitive inhibition of prostaglandin synthetase by 8-cis-12-trans-14-cis-eicosatrienoic acid has been reported to occur in vitro. No in vivo effects were observed, possibly due to rapid metabolic degradation of this fatty acid by beta-oxidation. The present study involved the evaluation of this compound in vivo, and the preparation and evaluation in vivo of its alpha and beta methyl-substituted analogs which retain the carbon skeleton of the parent compound, and which might be expected to be resistant to beta-oxidation. Using a newly developed radioimmunoassay for the total urinary metabolites of prostaglandin E, data were obtained that indicates that both the parent compound and its 2-methyl analog are prostaglandin synthetase inhibitors in vivo. The 2-methyl analog exhibited an unusually long duration of activity as compared to both indomethacin and the parent compound. The lengthened duration of action of the 2-methyl analog may be explained both by its possible resistance to beta-oxidation, and to possible alteration in rates of either fatty acid transport, or incorporation/release from triglycerides (acylation/deacylation of triglycerides).

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The synthesis and biological evaluation of a series of alpha, alpha-bis[(dialkylamino)alkyl]phenylacetamides, 2, are presented. These compounds are structurally related to the antiarrhythmic agent disopyramide (1) and in many cases were found to possess greater antiarrhythmic activity in coronary ligated dogs. Within this series of compounds, a separation of the antiarrhythmic properties from the unwanted cardiac depressant side effects observed with the parent compound, 7, was also often attained. A discussion of the structure-activity relationships within the series is presented; this work has culminated in the identidiction of compound 35 (disobutamide) as a candidate for clinical evaluation as an antiarrhythmic agent in man.

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A series of beta-spiro[pyrrolidinoindolines], 3a-d, was prepared and evaluated for their ability to bind to the glycine receptor. These compounds were also tested in vivo to determine if they would produce convulsant or anxiolytic effects. The target indolines were chosen because they represent rings A, B, E, and a portion of ring C of strychnine. Results of this study indicate that, in this series, an acetylindoline in the endo configuration and a tertiary amine, such as that of the pyrrolidine ring nitrogen, are required for biological activity. In all of the cases studied, the activity was of a convulsant rather than a relaxant nature. Excellent correlation was found to exist between the binding affinities to the strychnine site of the glycine receptor and clonic convulsions (ED50) and death (LD50) in the mouse.

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Crude synaptic membranes were isolated from rat pons, medulla and spinal cord by differential centrifugation. The specific binding of [3H]strychnine, obtained by subtracting from the bound radioactivity the amount not displaced by 50 micronm unlabeled strychnine, was saturable with a KD value of 12 nM. The dissociation constants (KD values) for the binding of several strychnine analogs to the strychnine site in vitro were determined and found to be highly correlated with the convulsant and lethal effects in the mouse. However, neither the biological activities in the mouse nor the binding activity in vitro correlated with the n-octanol-water distribution coefficients. The results are in accord with the concept that the [3H]strychnine binding site detected in vitro is the site of pharmacological activity in vivo.

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