Juan Pablo Cueva

Extensive Rigid Analogue Design Maps the Binding Conformation of Potent N-Benzylphenethylamine 5-HT2A Serotonin Receptor Agonist Ligands

Based on the structure of the superpotent 5-HT(2A) agonist 2-(4-bromo-2,5-dimethoxyphenyl)-N-[(2-methoxyphenyl)methyl]ethanamine, which consists of a ring-substituted phenethylamine skeleton modified with an N-benzyl group, we designed and synthesized a small library of constrained analogues to identify the optimal arrangement of the pharmacophoric elements of the ligand. Structures consisted of diversely substituted tetrahydroisoquinolines, piperidines, and one benzazepine. Based on the structure of (S,S)-9b, which showed the highest affinity of the series, we propose an optimal binding conformation. (S,S)-9b also displayed 124-fold selectivity for the 5-HT(2A) over the 5-HT(2C) receptor, making it the most selective 5-HT(2A) receptor agonist ligand currently known.

Synthesis and In Vitro Opioid Receptor Functional Antagonism of Methyl-Substituted Analogues 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 (JDTic)†

In previous structure-activity relationship (SAR) studies, (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, 3) was identified as the first potent and selective kappa-opioid receptor antagonist from the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of opioid antagonists. In the present study, we report the synthesis of analogues 8a-p of 3 and present their in vitro opioid receptor functional antagonism using a [(35)S]GTPgammaS binding assay. Compounds 8a-p are analogues of 3 containing one, two, or three methyl groups connected to the JDTic structure at five different positions. All the analogues with one and two added methyl groups with the exception of 8k had subnanomolar K(e) values at the kappa receptor. The three most potent analogues were the monomethylated (3R)-7-hydroxy-N-[(1S,2S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidine-1-yl]methyl}-2-methylbutyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (8a) and (3R)-7-hydroxy-N-[(1S)-1-{[(3R,4R)-4-(3-hydroxyphenyl)-3,4-dimethylpiperidin-1-yl]methyl}-(2-methylpropyl)]-3-methyl-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (8e) with K(e) values of 0.03 nM at the kappa receptor and (3R)-7-hydroxy-N-[(1S)-1-{[(3R,4R)-4-(3-methoxyphenyl)-3,4-dimethylpiperidin-1-yl]methyl}-2-methylpropyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxamide (8d) with K(e) = 0.037 nM at the kappa receptor. All three compounds were selective for the kappa receptor relative to the micro and delta receptors. Overall, the results from this study highlight those areas that are tolerant to substitution on 3.

Comparison of the enantiomers of (±)-doxanthrine, a high efficacy full dopamine D1 receptor agonist, and a reversal of enantioselectivity at D1 versus alpha2C adrenergic receptors

Parkinsons disease is a neurodegenerative condition involving the death of dopaminergic neurons in the substantia nigra. Dopamine D(1) receptor agonists are potential alternative treatments to current therapies that employ L-DOPA, a dopamine precursor. We evaluated the pharmacological profiles of the enantiomers of a novel dopamine D(1) receptor full agonist, doxanthrine (DOX) at D(1) and alpha(2C) adrenergic receptors. (+)-DOX displayed greater potency and intrinsic activity than (-)-DOX in porcine striatal tissue and in a heterologous D(1) receptor expression system. Studies in MCF7 cells, which express an endogenous human dopamine D(1)-like receptor, revealed that (-)-DOX was a weak partial agonist/antagonist that reduced the functional activity of (+)-DOX and dopamine. (-)-DOX had 10-fold greater potency than (+)-DOX at alpha(2C) adrenergic receptors, with an EC50 value of 4 nM. These findings demonstrate a reversed stereoselectivity for the enantiomers of DOX at D(1) and alpha(2C) receptors and have implications for the therapeutic utility of doxanthrine.

Probing the steric space at the floor of the D1 dopamine receptor orthosteric binding domain: 7α-, 7β-, 8α-, and 8β-methyl substituted dihydrexidine analogues

To probe the space at the floor of the orthosteric ligand binding site in the dopamine D(1) receptor, four methylated analogues of dihydrexidine (DHX) were synthesized with substitutions at the 7 and 8 positions. The 8α-axial, 8β-equatorial, and 7α-equatorial were synthesized by photochemical cyclization of appropriately substituted N-benzoyl enamines, and the 7β-axial analogue was prepared by an intramolecular Henry reaction. All of the methylated analogues displayed losses in affinity when compared to DHX (20 nM): 8β-Me(ax)-DHX (270 nM), 8α-Me(eq)-DHX (920 nM), 7β-Me(eq)-DHX (6540 nM), and 7α-Me(ax)-DHX (>10000 nM). Molecular modeling studies suggest that although the disruption of an aromatic interaction between Phe203(5.47) and Phe288(6.51) is the cause for the 14-fold loss in affinity associated with 8β-axial substitution, unfavorable steric interactions with Ser107(3.36) result in the more dramatic decreases in binding affinity suffered by the rest of the analogues.

Discovery of N-{4-[(3-hydroxyphenyl)-3-methylpiperazin-1-yl]methyl-2-methylpropyl}-4-phenoxybenzamide analogues as selective kappa opioid receptor antagonists.

There is continuing interest in the discovery and development of new κ opioid receptor antagonists. We recently reported that N-substituted 3-methyl-4-(3-hydroxyphenyl)piperazines were a new class of opioid receptor antagonists. In this study, we report the syntheses of two piperazine JDTic-like analogues. Evaluation of the two compounds in an in vitro [(35)S]GTPγS binding assay showed that neither compound showed the high potency and κ opioid receptor selectivity of JDTic. A library of compounds using the core scaffold 21 was synthesized and tested for their ability to inhibit [(35)S]GTPγS binding stimulated by the selective κ opioid agonist U69,593. These studies led to N-[(1S)-1-{[(3S)-4-(3-hydroxyphenyl)-3-methylpiperazin-1-yl]methyl}-2-methylpropyl]-4-phenoxybenzamide (11a), a compound that showed good κ opioid receptor antagonist properties. An SAR study based on 11a provided 28 novel analogues. Evaluation of these 28 compounds in the [(35)S]GTPγS binding assay showed that several of the analogues were potent and selective κ opioid receptor antagonists.

Analogues of doxanthrine reveal differences between the dopamine D1 receptor binding properties of chromanoisoquinolines and hexahydrobenzo[a]phenanthridines.

Efforts to develop selective agonists for dopamine D(1)-like receptors led to the discovery of dihydrexidine and doxanthrine, two bioisosteric β-phenyldopamine-type full agonist ligands that display selectivity and potency at D(1)-like receptors. We report herein an improved methodology for the synthesis of substituted chromanoisoquinolines (doxanthrine derivatives) and the evaluation of several new compounds for their ability to bind to D(1)- and D(2)-like receptors. Identical pendant phenyl ring substitutions on the dihydrexidine and doxanthrine templates surprisingly led to different effects on D(1)-like receptor binding, suggesting important differences between the interactions of these ligands with the D(1) receptor. We propose, based on the biological results and molecular modeling studies, that slight conformational differences between the tetralin and chroman-based compounds lead to a shift in the location of the pendant ring substituents within the receptor.

Effect of the 3- and 4-methyl groups on the opioid receptor properties of N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines.

N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidines (2a,b) are opioid receptor antagonists where the antagonist properties are not due to the type of N-substituent. In order to gain a better understanding of the contribution that the 3- and 4-methyl groups make to the pure antagonist properties of 2a,b, we synthesized analogues of 2a,b that lacked the 4-methyl (5a,b), 3-methyl (6a,b), and both the 3- and 4-methyl group (7a,b) and compared their opioid receptor properties. We found that (1) all N-methyl and N-phenylpropyl substituted compounds were nonselective opioid antagonists (2) all N-phenylpropyl analogues were more potent than their N-methyl counterparts, and (3) compounds 2a,b which have both a 3- and 4-methyl substituent, were more potent antagonists than analogues 5a,b, 6a,b, and 7a,b. We also found that the removal of 3-methyl substituent of N-methyl and N-phenylpropyl 3-methyl-4-(3-hydroxyphenyl)piperazines (8a,b) gives (4a,b), which are opioid antagonists.