Conformationally Restricted σ1 Receptor Antagonists from (-)-Isopulegol

Stereoselective Synthesis and Catalytical Application of Perillaldehyde-Based 3-Amino-1,2-diol Regioisomers

A library of regioisomeric monoterpene-based aminodiols was synthesised and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. The synthesis of the first type of aminodiols was achieved starting from (-)-8,9-dihydroperillaldehyde via reductive amination, followed by Boc protection and dihydroxylation with the OsO4/NMO system. Separation of formed stereoisomers resulted in a library of aminodiol diastereoisomers. The library of regioisomeric analogues was obtained starting from (-)-8,9-dihydroperillic alcohol, which was transformed into a mixture of allylic trichloroacetamides via Overman rearrangement. Changing the protecting group to a Boc function, the protected enamines were subjected to dihydroxylation with the OsO4/NMO system, leading to a 71:16:13 mixture of diastereoisomers, which were separated, affording the three isomers in isolated form. The obtained primary aminodiols were transformed into secondary derivatives. The regioselectivity of the ring closure of the N-benzyl-substituted aminodiols with formaldehyde was also investigated, resulting in 1,3-oxazines in an exclusive manner. To explain the stability difference between diastereoisomeric 1,3-oxazines, a series of comparative theoretical modelling studies was carried out. The obtained potential catalysts were applied in the reaction of aromatic aldehydes and diethylzinc with moderate to good enantioselectivities (up to 94% ee), whereas the opposite chiral selectivity was observed between secondary aminodiols and their ring-closed 1,3-oxazine analogues.

Thiophenpiperazine amide derivatives as new dual MOR and σ1R ligands for the treatment of pain

A new series of thiophenpiperazine amide derivatives as potent dual ligands for the μ-opioid (MOR) and sigma-1 (σ1R) receptors are reported. Compound 23 exhibited good affinity to σ1R (Ki = 44.7 ± 7.05 nM) and high selectivity to σ2R. Furthermore, Compound 23 exerted MOR agonism and σ1R antagonism and potent analgesic activity in animal moldes (the abdominal constriction test (ED50 = 3.83 mg/kg) and carrageenan-induced inflammatory hyperalgesia model (ED50 = 5.23 mg/kg)). We obtained new dual ligands that might serve as starting points for preparing targeted tools. Furthermore, 23 may be a useful chemical probe for understanding more fully analgesic effects associated with MOR agonism and σ1R antagonism.

[18F]Fluspidine-A PET Tracer for Imaging of σ1 Receptors in the Central Nervous System

σ1 receptors play a crucial role in various neurological and neurodegenerative diseases including pain, psychosis, Alzheimer's disease, and depression. Spirocyclic piperidines represent a promising class of potent σ1 receptor ligands. The relationship between structural modifications and σ1 receptor affinity and selectivity over σ2 receptors led to the 2-fluoroethyl derivative fluspidine (2, Ki = 0.59 nM). Enantiomerically pure (S)-configured fluspidine ((S)-2) was prepared by the enantioselective reduction of the α,β-unsaturated ester 23 with NaBH4 and the enantiomerically pure co-catalyst (S,S)-24. The pharmacokinetic properties of both fluspidine enantiomers (R)-2 and (S)-2 were analyzed in vitro. Molecular dynamics simulations revealed very similar interactions of both fluspidine enantiomers with the σ1 receptor protein, with a strong ionic interaction between the protonated amino moiety of the piperidine ring and the COO- moiety of glutamate 172. The 18F-labeled radiotracers (S)-[18F]2 and (R)-[18F]2 were synthesized in automated syntheses using a TRACERlab FX FN synthesis module. High radiochemical yields and radiochemical purity were achieved. Radiometabolites were not found in the brains of mice, piglets, and rhesus monkeys. While both enantiomers revealed similar initial brain uptake, the slow washout of (R)-[18F]2 indicated a kind of irreversible binding. In the first clinical trial, (S)-[18F]2 was used to visualize σ1 receptors in the brains of patients with major depressive disorder (MDD). This study revealed an increased density of σ1 receptors in cortico-striato-(para)limbic brain regions of MDD patients. The increased density of σ1 receptors correlated with the severity of the depressive symptoms. In an occupancy study with the PET tracer (S)-[18F]2, the selective binding of pridopidine at σ1 receptors in the brain of healthy volunteers and HD patients was shown.