4-[(8-Alkyl-8-azabicyclo[3.2.1]octyl-3-yl)-3-arylanilino]-N,N-diethylbenzamides: high affinity, selective ligands for the delta opioid receptor illustrate factors important to antagonist activity

Identification of Psychoplastogenic Tropanes Lacking Muscarinic Activity

Tropane-containing small molecules like scopolamine are a promising class of psychoplastogens. However, their potent antagonism of all muscarinic receptor subtypes presents the potential for undesirable anticholinergic side effects. In an effort to decouple their neuroplasticity-promoting effects from their muscarinic activity, we performed phenotypic structure-activity relationship studies across a variety of structurally distinct subclasses of tropanes. We discovered several novel tropanes capable of significantly increasing cortical neuronal growth while exhibiting drastically reduced activity at all muscarinic receptor subtypes compared to scopolamine.

N,N-dialkyl-4-[(8-azabicyclo[3.2.1]-oct-3-ylidene)phenylmethyl]benzamides, potent, selective delta opioid agonists

A series of N,N-dialkyl-4-(9-aryltropanylidenemethyl)benzamides was prepared. The lead compounds, 15a and 15c, exhibited extremely high affinity for the delta opioid receptor with excellent selectivity versus the micro opioid receptor. They were full agonists at the delta opioid receptor, as assessed by stimulation of GTPgammaS binding, and displayed antinociceptive activity.

Identification of (3R)-7-hydroxy-N-((1S)-1-[[(3R,4R)-4-(3-hydroxyphenyl)- 3,4-dimethyl-1-piperidinyl]methyl]-2-methylpropyl)-1,2,3,4-tetrahydro- 3-isoquinolinecarboxamide as a novel potent and selective opioid kappa receptor antagonist

(3R)-7-Hydroxy-N-((1S)-1-[[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethyl-1-piperidinyl]methyl]-2-methylpropyl)-1,2,3,4-tetrahydro-3-isoquinolinecarboxamide (JDTic) was identified as a potent and selective kappa opioid receptor antagonist. Structure-activity relationship (SAR) studies on JDTic analogues revealed that the 3R,4R stereochemistry of the 3,4-dimethyl-4-(3-hydroxyphenyl)piperidine core structure, the 3R attachment of the 7-hydroxy-1,2,3,4-tetrahydroisoquinoline group, and the 1S configuration of the 2-methylpropyl (isopropyl) group were all important to its kappa potency and selectivity. The results suggest that, like other kappa opioid antagonists such as nor-BNI and GNTI, JDTic requires a second basic amino group to express potent and selective kappa antagonist activity in the [(35)S]GTPgammaS functional assay. However, unlike previously reported kappa antagonists, JDTic also requires a second phenol group in rigid proximity to this second basic amino group. The potent and selective kappa antagonist properties of JDTic can be rationalized using the "message-address" concept wherein the (3R,4R)-3,4-dimethyl-4-(hydroxyphenyl)piperidinyl group represents the message, and the basic amino and phenol group in the N substituent constitutes the address. It is interesting to note the structural commonality (an amino and phenol groups) in both the message and address components of JDTic. The unique structural features of JDTic will make this compound highly useful in further characterization of the kappa receptor.

Piperazinyl benzamidines: synthesis and affinity for the delta opioid receptor

Piperazinyl benzamidines were prepared and found to bind to the rat delta (delta) opioid receptor. The most active compounds had a N,N-diethylcarboxamido group and a N-benzyl piperazine. The most potent among these was N,N-diethyl-4-[4-(phenylmethyl)-1-piperazinyl][2-(trifluoromethyl)phenyl]iminomethyl]benzamide (27) with a 1.22nM K(i) for the rat delta opioid receptor and ca. 1000 x selectivity relative to the mu opioid subtype.

Opioid peptide receptor studies. 15. Relative efficacy of 4-[(N-allyl-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide and related compounds at the cloned human delta-opioid receptor

Previous data obtained from both binding and functional assays demonstrated that (-)-4-[(N-allyl-3-methyl-4-piperidinyl)phenylamino]-N,N-diethylbenzamide [(-)-RTI5989-54] displays selective binding and full agonist activity relative to (+/-)-RTI5989-54 for the delta opioid receptor. The present study was conducted to evaluate the activities of structurally diverse opioid receptor delta ligands in the [(35)S]GTP-gamma-S binding assay, comparing the relationship between receptor binding, activation, efficacy, and intrinsic efficacy. The data, obtained with cloned human delta receptors, demonstrated that (-)-RTI5989-54 behaves like the highly selective delta agonist SNC80. Addition of the hydroxyl group to RTI5989-54 (RTI5989-61) or replacement of the allyl group with the trans-crotyl group on the piperidine nitrogen of RTI-5989-61 (RTI5989-62) increased binding affinity, produced full agonist activity, and decreased intrinsic efficacy at the delta opioid receptor. The order of potency for the EC(50) (GTP-gamma-S) was RTI5989-62 (0.20 nM) > RTI5989-61 (0.43 nM) > SNC80 (1.92 nM) > DPDPE (3.50 nM) > (-)-RTI5989-54 (17.6 nM) > (+/-)-RTI5989-54 (65.6 nM) > (+)-RTI5989-54 (483 nM). RTI5989-61 and RTI5989-62 were fully efficacious, but had intrinsic efficacy values that were 2.2-3.1 times lower than that of DPDPE and SNC80. Comparison of the binding K(i) in competitively inhibiting [(125)I]IOXY binding to the functional K(i) for delta antagonists [Ki (IOXY)/Ki (GTP-gamma-S)] shows that antagonists might antagonize agonist-evoked neurochemical effects with equal magnitude while occupying different proportions of target receptors.

Factors influencing agonist potency and selectivity for the opioid delta receptor are revealed in structure-activity relationship studies of the 4-[(N-substituted-4-piperidinyl)arylamino]-N,N-diethylbenzamides

A study of the effect of transposition of the internal nitrogen atom for the adjacent benzylic carbon atom in delta-selective agonists such as BW373U86 (1) and SNC-80 (2) has been undertaken. It was shown that high-affinity, fully efficacious, and delta opioid receptor-selective compounds can be obtained from this transposition. In addition to the N,N-diethylamido group needed as the delta address, the structural features identified to promote delta receptor affinity in the set of compounds studied included a cis relative stereochemistry between the 3- and 4-substituents in the piperidine ring, a trans-crotyl or allyl substituent on the basic nitrogen, the lack of a 2-methyl group in the piperidine ring, and either no substitution or hydroxyl substitution in the aryl ring not substituted with the N,N-diethylamido group. Structural features found to be important for mu affinity include hydroxyl substitution in the aryl ring, the presence of a 2-methyl group in a cis relative relationship to the 4-amino group as well as N-substituents such as cyclopropylmethyl. It was also determined that mu receptor affinity could be increased while maintaining delta receptor affinity, especially when hydroxyl-substituted compounds are considered. Additionally, it was discovered that the somewhat lower mu/delta selectivities observed for the piperidine compounds relative to the piperazine-based ligands appear to arise as a consequence of the carbon-nitrogen transposition which imparts an overall lower delta and higher mu affinity to the piperidine-based ligands. This higher affinity for the mu receptor, apparently intrinsic to the piperidine-based compounds, suggests that ligands of this class will more easily be converted to mu/delta combination agonists compared to the piperazine ligands such as 1. This is particularly important since analogues of 1, which show both mu- and delta-type activity, are now recognized as important for their strong analgesia and cross-canceling of many of the side effects found in agonists operating exclusively from either the delta or mu opioid receptor.