Synthesis and serotonin receptor affinities of a series of trans-2-(indol-3-yl)cyclopropylamine derivatives

Serotonin 2A Receptor (5-HT2AR) Agonists: Psychedelics and Non-Hallucinogenic Analogues as Emerging Antidepressants

Psychedelics make up a group of psychoactive compounds that induce hallucinogenic effects by activating the serotonin 2A receptor (5-HT2AR). Clinical trials have demonstrated the traditional psychedelic substances like psilocybin as a class of rapid-acting and long-lasting antidepressants. However, there is a pressing need for rationally designed 5-HT2AR agonists that possess optimal pharmacological profiles in order to fully reveal the therapeutic potential of these agonists and identify safer drug candidates devoid of hallucinogenic effects. This Perspective provides an overview of the structure-activity relationships of existing 5-HT2AR agonists based on their chemical classifications and discusses recent advancements in understanding their molecular pharmacology at a structural level. The encouraging clinical outcomes of psychedelics in depression treatment have sparked drug discovery endeavors aimed at developing novel 5-HT2AR agonists with improved subtype selectivity and signaling bias properties, which could serve as safer and potentially nonhallucinogenic antidepressants. These efforts can be significantly expedited through the utilization of structure-based methods and functional selectivity-directed screening.

Recent advances in the catalytic cyclopropanation of unsaturated compounds with diazomethane

The main achievements and development trends of the past 10–15 years related to the catalytic cyclopropanation of unsaturated compounds with diazomethane are integrated and analyzed. The attention is focused on the most efficient catalysts based on palladium compounds. Data on the effects of substrate structure and nature of catalyst components on the regio- and stereoselectivity of these reactions are systematized. Characteristic features of safe methods for diazomethane generation are considered, including the use of membrane technologies and continuous-flow and in situ preparation methods, which have prospects for industrial application.

The bibliography includes 281 references.

Low Basicity as a Characteristic for Atypical Ligands of Serotonin Receptor 5-HT2

Serotonin receptors are extensively examined by academic and industrial researchers, due to their vital roles, which they play in the organism and constituting therefore important drug targets. Up to very recently, it was assumed that the basic nitrogen in compound structure is a necessary component to make it active within this receptor system. Such nitrogen interacts in its protonated form with the aspartic acid from the third transmembrane helix (D3x32) forming a hydrogen bond tightly fitting the ligand in the protein binding site. However, there are several recent studies that report strong serotonin receptor affinity also for compounds without a basic moiety in their structures. In the study, we carried out a comprehensive in silico analysis of the low-basicity phenomenon of the selected serotonin receptor ligands. We focused on the crystallized representatives of the proteins of 5-HT_1B, 5-HT_2A, 5-HT_2B, and 5-HT_2C receptors, and examined the problem both from the ligand- and structure-based perspectives. The study was performed for the native proteins, and for D3x32A mutants. The investigation resulted in the determination of nonstandard structural requirements for activity towards serotonin receptors, which can be used in the design of new nonbasic ligands.

Chemistry and Structure-Activity Relationships of Psychedelics

This chapter will summarize structure-activity relationships (SAR) that are known for the classic serotonergic hallucinogens (aka psychedelics), focusing on the three chemical types: tryptamines, ergolines, and phenethylamines. In the brain, the serotonin 5-HT_2A receptor plays a key role in regulation of cortical function and cognition, and also appears to be the principal target for hallucinogenic/psychedelic drugs such as LSD. It is one of the most extensively studied of the 14 known types of serotonin receptors. Important structural features will be identified for activity and, where possible, those that the psychedelics have in common will be discussed. Because activation of the 5-HT_2A receptor is the principal mechanism of action for psychedelics, compounds with 5-HT_2A agonist activity generally are quickly discarded by the pharmaceutical industry. Thus, most of the research on psychedelics can be related to activation of 5-HT_2A receptors. Therefore, much of the discussion will include not only clinical or anecdotal studies, but also will consider data from animal models as well as a certain amount of molecular pharmacology where it is known.

Cyclopropyl-tryptamine analogues: synthesis and biological evaluation as 5-HT(6) receptor ligands

Conformational restrictions: Based on the pharmacophore model for 5-HT(6) receptor ligands (shown), tryptamine analogues bearing a cyclopropyl ring on the α-position of the tryptamine side chain were synthesized and evaluated against 5-HT receptors. N,N-Dimethyl-1-arylsulfonyltryptamine derivatives exhibited promising selectivity for 5-HT(6) over 5-HT(1a) and 5-HT(4) receptors and interesting activity against 5-HT(6) (K(i) =∼0.15 μM; IC(50) =∼0.20 μM).

trans-2-(2,5-Dimethoxy-4-iodophenyl)cyclopropylamine and trans-2-(2,5-dimethoxy-4-bromophenyl)cyclopropylamine as potent agonists for the 5-HT(2) receptor family

A strategy to replace the ethylamine side chain of 2,5-dimethoxy-4-iodoamphetamine (DOI, 1a), and 2,5-dimethoxy-4-bromoamphetamine (DOB, 1b) with a cyclopropylamine moiety was successful in leading to compounds with high affinity at the 5-HT₂ family of receptors; and the more potent stereoisomer of the cyclopropane analogues had the expected (−)-(1R,2S)-configuration. Screening for affinity at various serotonin receptor subtypes, however, revealed that the cyclopropane congeners also had increased affinity at several sites in addition to the 5-HT_2A and 5-HT_2B receptors. Therefore, at appropriate doses – although (−)-4 and (−)-5 may be useful as tools to probe 5-HT₂ receptor function – one would need to be mindful that their selectivity for 5-HT_2A receptors is somewhat less than for DOI itself.

The Kulinkovich Reaction in the Synthesis of Constrained N,N-Dialkyl Neurotransmitter Analogues

An intermolecular Ti(IV)-mediated cyclopropanation reaction has been used to synthesize substituted 2-phenylcyclopropylamines and constrained analogues of the neurotransmitters histamine and tryptamine. Many hydroxy- and methoxy-substituted phenylcyclopropylamines are known to inhibit monoamine oxidase and have been shown to mimic hallucinogens. These compounds were made in 1 to 5 steps from readily available starting materials.

Conformationally restricted homotryptamines. 2. Indole cyclopropylmethylamines as selective serotonin reuptake inhibitors

A series of indole cyclopropylmethylamines were found to be potent serotonin reuptake inhibitors. Nitrile substituents at the 5 and 7 positions of the indole ring gave high affinity for hSERT, and the preferred cyclopropane stereochemistry was determined to be (1S,2S)-trans. The cis-cyclopropanes had 20- to 30-fold less affinity than the trans, and the preferred cis stereochemistry was (1R,2S)-cis. Substitution of the indole N-1 position with methyl or ethyl groups gave a 10- to 30-fold decrease in affinity for hSERT, suggesting either a hydrogen-bonding interaction or limited steric tolerance in the region of the indole nitrogen. Compound (+)-12a demonstrated potent hSERT binding (Ki = 0.18 nM) in vitro and was more than 1000-fold less potent at hDAT, hNET, 5-HT1A, and 5-HT6. In vivo, (+)-12a produced robust, dose-dependent increases in extracellular serotonin in rat frontal cortex typical of a selective serotonin reuptake inhibitor. The maximal response produced by (+)-12a was similar to that of fluoxetine but at an approximately 10-fold lower dose.

Catalytic Asymmetric Diazoacetate Cyclopropanation of 1-Tosyl-3-vinylindoles. A Route to Conformationally Restricted Homotryptamines

[reaction: see text] Substituted 1-tosyl-3-vinylindoles undergo catalytic asymmetric cyclopropanation with ethyl- and tert-butyldiazoacetate to afford N-protected trans-2-(indol-3-yl)-1-cyclopropanecarboxylic esters in good yield and high enantiomeric excess (81-88% ee). The resulting cycloadducts are demonstrated to be useful intermediates for the synthesis of conformationally restricted, homotryptamine-like analogues such as BMS-505130.

Total asymmetric synthesis of (?)-Phenylhistine, (?)-Aurantiamine and related compounds. Part I

A new general, short, and efficient strategy for the construction of dehydro-diketopiperazines was developed. Horner-Emmons type coupling between a phosphinyl glycine ester and a formyl heterocycle is the key coupling reaction, which proceeds in good-to-excellent yields on several sterically-hindered substrates. Moreover, racemization of the parent L-amino acids is avoided as a result of the mild basic conditions used. The selection of the NH protective group of the formyl heterocycle was crucial. N-tosylated heterocycles proved ideal for this reaction sequence. Thus, the title compounds, (-)-Phenylhistine and (-)-Aurantiamine, were prepared in high yield (four steps, 47% overall) and optical purity. Furthermore, the synthesis of unnatural derivatives including an indole analogue was successfully completed.

Development of an Indole Safety-Catch Linker Using Analytical Constructs

The development, evaluation, and application of a novel safety-catch linker for solid-phase synthesis based on an N-tosylindole is reported. The development of this linker using analytical constructs to aid analysis is discussed.

Further studies on oxygenated tryptamines with LSD-like activity incorporating a chiral pyrrolidine moiety into the side chain

The enantiomers of 3-(N-methylpyrrolidin-2-ylmethyl)-5-methoxyindole, 1, and 3-(N-methylpyrrolidin-2-ylmethyl)-4-hydoxyindole, 3, were prepared using an asymmetric synthesis that employed (+)- or (-)-proline. A new approach was developed that had certain advantages over the synthesis originally reported for the isomers of 1. (+/-)-3-(N-Methylpyrrolidin-3-yl)-4-hydroxyindole, 5, was also prepared as a rigid analogue of psilocin and compared with its 5-methoxy counterpart 4. Radioligand competition assays were used to assess the affinity of compounds for the 5-HT(2A) receptor labeled with the agonist ligand [(125)I]DOI and the antagonist ligand [(3)H]MDL100907. Two-lever drug discrimination assays in rats trained to discriminate either LSD or DOI from saline were employed to assess the hallucinogen-like behavioral properties of these rigid tryptamine analogues. The receptor binding assay results clearly demonstrated a stereochemical preference for the R enantiomers that did not discriminate the position of the oxygen function. The receptor is 10-20-fold more selective for the R isomers. The affinities of the R enantiomers were virtually identical for both 1 and 3 at the agonist-labeled receptor, while racemic 4 and 5 had about one-tenth the affinity. The drug discrimination data in both LSD- and DOI-trained rats paralleled the binding data using [(125)I]DOI displacement. Both (R)-1 and (R)-3 are about equipotent, comparable to DOI in activity but about 10-fold less potent than LSD. Compound 4 produced only partial substitution, even at a dose nearly 5-fold higher than for (R)-1. Based on conformational energies, it seems doubtful that these compounds bind to the 5-HT(2A) receptor in an ergoline-like conformation. The results also suggest that both 1 and 3 would possess LSD-like psychopharmacology in humans.