Synthesis and dopamine agonist properties of (+-)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano [4,3-b]-1,4-oxazin-9-ol and its enantiomers.

The dopamine agonist profile of (+-)-trans-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano [4,3-b]-1,4-oxazin-9-ol (16a) and its enantiomers (16b-c) was examined. Racemic 16a exhibited moderate affinity for the dopamine (DA) D2 receptor labeled with the DA antagonist ligand [3H]haloperidol and moderate in vivo activity; it attenuated gamma-butyrolactone-stimulated DA synthesis, decreased DA neuronal firing of substantia nigra DA neurons, and inhibited exploratory locomotor activity in rats, a profile consistent with a DA autoreceptor agonist mechanism of action. The (+)-enantiomer 16b possessed greater DA receptor affinity with the agonist ligand [3H]-N-propylnorapomorphine than with the antagonist ligand. In rats it potently inhibited DA synthesis and neuronal firing and also inhibited exploratory locomotion. The (-)-enantiomer, on the other hand, did not have significant activity in any of these tests. This profile indicates that like many other rigid DA agonists, the dopaminergic activity resides in one enantiomer, in this case the (+)-enantiomer 16b. On the basis of single-crystal X-ray analysis of a key intermediate, the absolute configuration of 16b was found to be 4aR, 10bR.

1,3-Dialkyl-4-(iminoarylmethyl)-1H-pyrazol-5-ols. A series of novel potential antipsychotic agents.

2-(Diethylamino)-N-[4-(2-fluorobenzoyl)-1,3-dimethyl-1H-pyrazol-5-yl] acetamide (1) was recently found to have an antipsychotic-like profile in behavioral animal tests but, unlike clinically available antipsychotic agents, did not interact with dopamine receptors. Compound 1 was apparently metabolized to (5-amino-1,3-dimethyl-1H-pyrazol-4-yl)(2-fluorophenyl)methanone (2), which was both active in the behavioral animal tests and toxic. The synthesis and pharmacological evaluation of a series of 1,3-dialkyl-4-(iminoarylmethyl)-1H-pyrazol-5-ols are described in which the hydroxy and imine functionalities were selected as possible isosteric replacements for the amino and ketone groups of the earlier series. The initial target, 1,3-dimethyl-4-(iminophenylmethyl)-1H-pyrazol-5-ol (28), like known antipsychotics, reduced spontaneous locomotion in mice at doses that did not cause ataxia, and unlike known agents, it did not bind to D2 dopamine receptors in vitro. An examination of the SAR of related compounds indicated that maximal activity was obtained with analogues containing methyl groups at the 1- and 3-positions on the pyrazole ring and with a 3-chloro substituent on the phenyl ring. Replacement of the hydrogen atom of the imine moiety with various substituents led to loss of activity. Attempts to synthesize the 2-fluorophenyl compound analogous to 2 resulted in ring-closure to 1,3-dimethyl[1]benzopyrano[2,3-c]pyrazol-4-(1H)-one (65). 4-[(3-Chlorophenyl)iminomethyl]-1,3-dimethyl-1H-pyrazol-5-ol (41) was evaluated in additional tests. It inhibited conditioned avoidance responding in both rats and monkeys but, unlike available antipsychotic drugs, did not elicit dystonic movements in a primate model of antipsychotic-induced extrapyramidal side effects.