Decahydrobenzoquinolin-5-one sigma receptor ligands: Divergent development of both sigma 1 and sigma 2 receptor selective examples

Small Molecules Selectively Targeting Sigma-1 Receptor for the Treatment of Neurological Diseases

The sigma-1 (σ1) receptor, an enigmatic protein originally classified as an opioid receptor subtype, is now understood to possess unique structural and functional features of its own and play critical roles to widely impact signaling transduction by interacting with receptors, ion channels, lipids, and kinases. The σ1 receptor is implicated in modulating learning, memory, emotion, sensory systems, neuronal development, and cognition and accordingly is now an actively pursued drug target for various neurological and neuropsychiatric disorders. Evaluation of the five selective σ1 receptor drug candidates (pridopidine, ANAVEX2-73, SA4503, S1RA, and T-817MA) that have entered clinical trials has shown that reaching clinical approval remains an evasive and important goal. This review provides up-to-date information on the selective targeting of σ1 receptors, including their history, function, reported crystal structures, and roles in neurological diseases, as well as a useful collation of new chemical entities as σ1 selective orthosteric ligands or allosteric modulators.

Asymmetric Dearomative Cascade Multiple Functionalizations of Activated N-Alkylpyridinium and N-Alkylquinolinium Salts

An enantioselective cascade reaction of N-alkylpyridinium and -quinolinium salts with o-hydroxybenzylideneacetones to access fused polyheterocycles through cross dienamine-mediated addition followed by trapping of the dearomatized enamine-type intermediates and aminal formation has been developed. A cascade assembly of N-benzyl-4-methylpyridinium salt and cyclic 2,4-dienones is further disclosed to give bridged frameworks via repetitive dearomatization and aromatization activation.

Radiosynthesis and preclinical evaluation of [11 C]Cimbi-701 - Towards the imaging of cerebral 5-HT7 receptors

The serotonin 7 (5-HT7 ) receptor is suggested to be involved in a broad variety of CNS disorders, but very few in vivo tools exist to study this important target. Molecular imaging with positron emission tomography (PET) would enable an in vivo characterization of the 5-HT7 receptor. However, no clinical PET radiotracer exists for this receptor, and thus we aimed to develop such a tracer. In this study, we present the preclinical evaluation of [11 C]Cimbi-701. Cimbi-701 was synthesized in a one-step procedure starting from SB-269970. Its selectivity profile was determined using an academic screening platform (NIMH Psychoactive Drug Screening Program). Successful radiolabeling of [11 C]Cimbi-701 and subsequent in vivo evaluation was conducted in rats, pigs and baboon. In vivo specificity was investigated by 5-HT7 and σ receptor blocking studies. P-gp efflux transporter dependency was investigated using elacridar. [11 C]Cimbi-701 could successfully be synthesized. Selectivity profiling revealed high affinity for the 5-HT7 (Ki = 18 nM), σ-1 (Ki = 9.2 nM) and σ-2 (Ki = 1.6 nM) receptors. In rats, [11 C]Cimbi-701 acted as a strong P-gp substrate. After P-gp inhibition, rat brain uptake could specifically be blocked by 5-HT7 and σ receptor ligands. In pig, high brain uptake and specific 5-HT7 and σ-receptor binding was found for [11 C]Cimbi-701 without P-gp inhibition. Finally, low brain uptake was found in baboons. Both the specific σ-receptor binding and the low brain uptake of [11 C]Cimbi-701 displayed in baboon discouraged further translation to humans. Instead, we suggest exploration of this structural class as results indicate that selective 5-HT7 receptor imaging might be possible when more selective non-P-gp substrates are identified.

Development and Evaluation of Two Potential 5-HT7 Receptor PET Tracers: [18F]ENL09 and [18F]ENL10

The latest addition to the serotonin (5-HT) receptor family is the 5-HT₇ receptor (5-HT₇R). This receptor has gained interest as a drug target due to its involvement in various disorders such as depression or schizophrenia. There is currently no clinically validated positron emission tomography (PET) tracer for the 5-HT₇R available. But, the (arylpiperazinyl-butyl)oxindole scaffold provides a promising lead structure for this purpose. Here, we synthesized 12 (arylpiperazinyl-butyl)oxindole derivatives and in vitro affinity screening identified two structures with suitable affinity and selectivity to be radiolabeled and tested as 5-HT₇R selective PET tracers. Next, the radiolabeled products [¹⁸F]ENL09 and [¹⁸F]ENL10 were evaluated as PET tracers in rats. Both tracers were found to be P-gp substrates, but after P-gp inhibition the brain uptake showed a regional distribution in line with the known 5-HT₇R distribution.  The [¹⁸F]ENL10 brain binding was displaceable with a 5-HT₇R selective ligand, whereas [¹⁸F]ENL09 was not. We find that [¹⁸F]ENL10 is a promising 5-HT₇R selective PET tracer candidate that should be investigated in higher species.