dihydrexidine and dinapsoline

Although the dopaminergic pharmacology of the D1 receptor full agonists, dinapsoline, dihydrexidine and the prodrug ABT-431 have been studied, no information is available on the ability of these agonists to substitute for the D1 agonist SKF 38393 in rats trained to discriminate this compound from vehicle. The present study was designed to characterize the potential D1 discriminative stimulus effects of these compounds. The selective dopamine D1-receptor agonists dihydrexidine [(+/-)-trans-10,11-dihydroxy-5,6,6a,7,8,12b-hexahydrobenzo[a] phenanthridine hydrochloride], ABT-431 [(-)-trans-9,10-diacetyloxy-2-propyl-4,5,5a,6,7,11b-hexahydro-3-thia-5-azacyclopent-1-ena[c]phenanthrene hydrochloride], the diacetyl prodrug derivative of A-86929, and dinapsoline [9-dihydroxy-2,3,7,11b-tetrahydro-1H-naph[1,2,3-de]isoquinoline] were studied in rats trained to discriminate racemic SKF 38393 [(+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol], a selective D1 receptor partial agonist from vehicle. All of the agonists substituted fully for the discriminative stimulus effects of SKF 38393. The rank order of potency for substitution was ABT-431 > dinapsoline > dihydrexidine > SKF 38393. The D1 receptor antagonist, SCH 23390, blocked the discriminative stimulus effects of SKF 38393. The D3/D2-receptor agonist PD 128,907 [S(+)-(4aR,10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]-benzopyrano[4,3-b]-1,4-oxazin-9-ol] did not substitute up to doses that produced profound rate-suppressant effects. Thus, consistent with their D1 receptor pharmacology, the full D1-receptor agonists substituted completely for the discriminative stimulus of SKF 38393.

Topics: 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine; Animals; Appetitive Behavior; Conditioning, Operant; Discrimination Learning; Dopamine Agonists; Drug Interactions; Isoquinolines; Male; Motivation; Naphthols; Phenanthridines; Prodrugs; Pyridines; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Stereoisomerism; Structure-Activity Relationship; Tetrahydronaphthalenes

In an analogy to the potent catechol dopamine D1 agonists dihydrexidine (1) and dinapsoline (2), benzo rings were fused onto the structures of the dopamine D2-selective agonists quinelorane (3) and quinpirole (4). Each of the phenyl ring-substituted derivatives had significant affinity for D2 receptors, albeit somewhat lower than the two parent compounds, 3 and 4. Compounds with N-propyl and N-allyl substituents (5b, 5c, 6c, and 6d) had higher affinity for the D2 dopamine receptor than did their corresponding secondary amines (5a and 6a). Slightly different effects on affinity of an n-propyl and an n-allyl group in the new analogues of 3 and 4 suggest that different binding orientations may be invoked at the receptor.

Topics: Animals; Binding, Competitive; Dopamine Agonists; In Vitro Techniques; Isoquinolines; Male; Naphthols; Neostriatum; Quinolines; Radioligand Assay; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, Dopamine D2; Structure-Activity Relationship

The present work reports the synthesis and preliminary pharmacological characterization of 8,9-dihydroxy-2,3,7,11b-tetrahydro-1H-naph[1,2,3-de] isoquinoline (4, dinapsoline). This molecule was designed to conserve the essential elements contained in our D1 agonist pharmacophore model (i.e., position and orientation of the nitrogen, hydroxyls, and phenyl rings). It involved taking the backbone of dihydrexidine [3; (+/-)-trans-10, 11-dihydroxy-5,6,6a,7,8,12b-hexahydrobenzo[a] phenanthridine], the first high-affinity full D1 agonist, and tethering the two phenyl rings of dihydrexidine through a methylene bridge and removing the C(7)-C(8) ethano bridge. Preliminary molecular modeling studies demonstrated that these modifications conserved the essential elements of the hypothesized pharmacopore. Dinapsoline 4 had almost identical affinity (KI = 5.9 nM) to 3 at rat striatal D1 receptors and had a shallow competition curve (nH = 0.66) that suggested agonist properties. Consistent with this, in both rat striatum and C-6-mD1 cells, dinapsoline 4 was a full agonist with an EC50 of ca. 30 nM in stimulating synthesis of cAMP via D1 receptors. The design and synthesis of dinapsoline 4 provide a powerful test of the model of the D1 pharmacophore we have developed and provide another chemical series that can be useful probes for the study of D1 receptors. An interesting property of 3 is that it also has relatively high D2 affinity (K0.5 = 50 nM) despite having an accessory phenyl ring usually though to convey D1 selectivity. Dinapsoline 4 was found to have even higher affinity for the D2 receptor (K0.5 = 31 nM) than 3. Because of the high affinity of 4 for D2 receptors, it and its analogs can be powerful tools for exploring the mechanisms of "functional selectivity" (i.e., that 3 is an agonist at some D2 receptors, but an antagonist at others). Together, these data suggest that 4 and its derivatives may be powerful tools in the study of dopamine receptor function and also have potential clinical utility in Parkinson's disease and other conditions where perturbation of dopamine receptors is useful.

Topics: Adenylyl Cyclases; Animals; Benzazepines; Corpus Striatum; Cyclic AMP; Dopamine Agonists; Dopamine Antagonists; Isoquinolines; Macaca mulatta; Male; Naphthols; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, Dopamine D2; Tumor Cells, Cultured