Synthesis and transporter binding properties of (R)-2 beta, 3 beta- and (R)-2 alpha, 3 alpha-diaryltropanes

The patent review of the biological activity of tropane containing compounds

INTRODUCTION

Tropane-derived medications have historically played a substantial role in pharmacotherapy. Both natural and synthetic derivatives of tropane find application in addressing diverse medical conditions. Prominent examples of tropane-based drugs include hyoscine butylbromide, recognized for its antispasmodic properties, atropine, employed as a mydriatic, maraviroc, known for its antiviral effects. trospium chloride, utilized as a spasmolytic for overactive bladder, and ipratropium, a bronchodilator.

AREAS COVERED

We compiled patents pertaining to the biological activity of substances containing tropane up to the year 2023 and categorized them according to the specific type of biological activity they exhibit. ScienceFinder, ScienceDirect, and Patent Guru were used to search for scientific articles and patent literature up to 2023.

EXPERT OPINION

Pharmaceutical researchers in academic and industrial settings have shown considerable interest in tropane derivatives. Despite this, there remains a substantial amount of work to be undertaken. A focused approach is warranted for the exploration and advancement of both natural and synthetic bioactive molecules containing tropane, facilitated through collaborative efforts between academia and industry. Leveraging contemporary techniques and technologies in medicinal and synthetic chemistry, including high throughput screening, drug repurposing,and biotechnological engineering, holds the potential to unveil novel possibilities and accelerate the drug discovery process for innovative tropane-based pharmaceuticals.

Synthesis and Monoamine Transporter Binding Properties of 2,3-Diaryltropanes

Synthetic procedures were developed for the synthesis of 2beta,3beta- and 2alpha,3alpha-diaryltropanes. These compounds are analogues of the 3-aryltropane-2beta-carboxylic acid methyl ester class of monoamine uptake inhibitors, where the 2beta-carbomethoxy group has been replaced by an aryl group. The compounds were evaluated for inhibition of radioligand binding at the dopamine, norepinephrine, and serotonin transporters (DAT, NET, and 5-HTT, respectively). The results showed that the replacement of the 2beta-carbomethoxy group in the 3-aryltropane class with a 2beta-aryl group led to compounds possessing very similar monoamine transporter binding properties. However, the 2beta,3beta-diaryltropanes tended to be more potent at the DAT and more selective for the DAT relative to the NET and 5-HTT. One of the most interesting compounds was 3beta-(4-methylphenyl)-2beta-(4-methylphenyl)tropane (3d), which showed an IC50 of 1.23 nM at the DAT with 289- and 185-fold selectivity for the DAT relative to the NET and 5-HTT. The 2alpha,3alpha-diaryltropanes were much less potent at all three transporters than 2beta,3beta-diaryltropanes.

Monoamine Transporter Binding, Locomotor Activity, and Drug Discrimination Properties of 3-(4-Substituted-phenyl)tropane-2-carboxylic Acid Methyl Ester Isomers

The monoamine transporter binding properties, gross behavior, and locomotor activity effects in mice and drug discrimination results in cocaine-trained rats of the 2 beta,3beta-, 2 beta,3 alpha-, 2 alpha,3beta-, and 2 alpha,3 alpha-isomers of several 3-(4-substituted-phenyl)tropane carboxylic acid methyl esters were compared (2a-f, 3a-f, 4a-f, and 5b,c). The 2 beta,3beta-isomer showed the highest affinity for the dopamine transporter (DAT), and the 2 beta,3 alpha-isomer showed the next highest affinity. The order of potency for the 2 beta,3beta-isomer is 4'-chloro (2c) = 4'-iodo (2e) > 4'-bromo (2d) = 4'-methyl (2f) > 4'-fluoro (2b) > 4'-hydrogen (2a). In the case of the 2 beta,3 alpha-isomer, the order of affinity was 4'-bromo (3d) > 4'-iodo (3e) = 4'- chloro (3c) > 4'-methyl (3f) > 4'-fluoro (3b) > 4'-hydrogen (3a). The 4'-hydrogen, 4'-fluoro, and 4'-methyl 2 alpha,3beta-isomers, 4a, 4b, and 4f, had the lowest affinity for the DAT. While most of the compounds showed their highest affinity at the DAT, none were selective relative to the other two monoamine transporters. In general, the 2 alpha,3 alpha- and 2 alpha,3beta-isomers were more toxic (death and convulsions) than the 2 beta,3beta- and 2 beta,3 alpha-isomers. With the exception of the 2 alpha,3 alpha-isomers, all compounds produced the locomotor activity stimulation typical of dopaminergic drugs. The ED(50) ranges for the 2 beta,3beta- (2a-f), 2 beta,3 alpha- (3a-f), and 2 alpha,3beta-isomers (4a-f) in the locomotor assay were 0.1-1.2, 6.6-21.8, and 2.4-11.7 mg/kg, respectively. With the exception of the 2 alpha,3 alpha-isomer, all compounds generalized to cocaine. The 2 beta,3beta-isomers were at least 10-fold more potent than cocaine and the other three sets of isomers in this test.

Synthesis and Monoamine Transporter Binding of 2-(Diarylmethoxymethyl)-3β-aryltropane Derivatives

3 beta-Aryltropane analogues wherein the 2-position was substituted with various diarylmethoxyalkyl groups were synthesized and evaluated for binding at the dopamine transporter (DAT), serotonin transporter (SERT), norepinephrine transporter (NET), and muscarinic (M(1)) receptors. The 2 beta-analogues 9a-i generally demonstrated high to moderate binding affinities (K(i) = 34-112 nM) at the DAT with good selectivity over SERT, NET, and M(1) receptors. Alternatively, the 2 alpha-isomers 10a-i were 10-fold less potent at the DAT with poor selectivity over SERT. These SAR studies provide further evidence for the varied binding requirements of structurally diverse tropane-based ligands and support future studies to elucidate DAT binding requirements in relation to cocaine-like behavioral endpoints.

Synthesis and biological evaluation of 2-substituted 3beta-tolyltropane derivatives at dopamine, serotonin, and norepinephrine transporters

A series of eight 2-substituted 3-tolyltropane derivatives were synthesized, and the in vitro and in vivo biological activities as dopamine uptake inhibitors were determined. From the in vitro structure-activity data, it is apparent that a tolyl group in the 2-position, independent of the stereochemical attachment to the tropane ring system, provided compounds (9-12, 14) that exhibit high-affinity binding at the dopamine transporter (DAT). Although a slight stereochemical preference in binding affinity at the DAT was observed for the 2beta-(R)-alcohol 10 over the 2beta-(S)-isomer 11, no significant differences in behavioral effects were observed. Furthermore, despite a relatively low potency of 10 for the inhibition of dopamine uptake compared to its affinity for the DAT, its behavioral profile did not vary significantly from cocaine. These data indicate that a behavioral characterization of compounds is a critical feature of efforts to discover pharmacological treatments for cocaine abuse.