Palladium asymmetric reduction of β-carboline imines mediated by chiral auxiliaries assisted by microwave irradiation

Enantioselective Imine Reduction of Dihydro-β-carbolines by Fe-Thiosquaramide Catalyst

Enantioselective imine reduction of dihydro-β-carbolines (DHBCs) is a reliable and powerful tool to construct bioactive chiral tetrahydro-β-carbolines (THBCs). Here, we report an efficient enantioselective imine reduction employing in situ generated Fe-thiosquaramides (Fe-TSQs) 3a and 3b as asymmetric organometallic catalysts to produce chiral THBCs (2a-h). The catalyst 3a at 15 mol % was found to be suitable for the substrates with alkyl and aryl groups which afford corresponding chiral THBCs with excellent enantioselectivities (up to ee 99%).

Bifunctional thiosquaramide catalyzed asymmetric reduction of dihydro-β-carbolines and enantioselective synthesis of (-)-coerulescine and (-)-horsfiline by oxidative rearrangement

Tetrahydro-β-carboline (THBC) is a tricyclic ring system that can be found in a large number of bioactive alkaloids. Herein, we report a simple and efficient method for the synthesis of enantiopure THBCs through a chiral thiosquaramide (11b) catalyzed imine reduction of dihydro-β-carbolines (17a-f). The in situ generated Pd-H employed as hydride source in the reaction of differently substituted chiral THBCs (18a-f) afforded high selectivities (R isomers, up to 96% ee) and good isolated yields (up to 88%). Moreover, the chiral thiosquaramide used also afforded exceptional catalyst activity in the syntheses of (-)-coerulescine (5) and (-)-horsfiline (6) with excellent enantioselectivities up to 98% and 93% ee, respectively, via an enantioselective oxidative rearrangement approach.

Discovery of a Teraryl Oxazolidinone Compound (S)-N-((3-(3-Fluoro-4-(4-(pyridin-2-yl)-1H-pyrazol-1-yl)phenyl)-2-oxooxazolidin-5-yl)methyl)acetamide Phosphate as a Novel Antimicrobial Agent with Enhanced Safety Profile and Efficacies

A series of novel teraryl oxazolidinone compounds was designed, synthesized, and evaluated for their antimicrobial activity and toxicities. The compounds with aromatic N-heterocyclic substituents at the 4-position of pyrazolyl ring showed better antibacterial activity against the tested bacteria than other compounds with different patterns of substitution. Among all potent compounds, 10f exhibited promising safety profile in MTT assays and in hERG K(+) channel inhibition test. Furthermore, its phosphate was found to be highly soluble in water (47.1 mg/mL), which is beneficial for the subsequent in vivo test. In MRSA systemic infection mice models, 10f phosphate exerted significantly improved survival protection compared with linezolid. The compound also demonstrated high oral bioavailability (F = 99.1%). Moreover, from the results of in vivo toxicology experiments, 10f phosphate would be predicted to have less bone marrow suppression.

(-)-Meptazinol-melatonin hybrids as novel dual inhibitors of cholinesterases and amyloid-β aggregation with high antioxidant potency for Alzheimer's therapy

The multifactorial pathogenesis of Alzheimer's disease (AD) implicates that multi-target-directed ligands (MTDLs) intervention may represent a promising therapy for AD. Amyloid-β (Aβ) aggregation and oxidative stress, two prominent neuropathological hallmarks in patients, play crucial roles in the neurotoxic cascade of this disease. In the present study, a series of novel (-)-meptazinol-melatonin hybrids were designed, synthesized and biologically characterized as potential MTDLs against AD. Among them, hybrids 7-7c displayed higher dual inhibitory potency toward cholinesterases (ChEs) and better oxygen radical absorbance capacity (ORAC) than the parental drugs. Furthermore, compound 7c could effectively inhibit Aβ self-aggregation, showed favorable safety and the blood-brain barrier (BBB) permeability. Therefore, 7c may serve as a valuable candidate that is worthy of further investigations in the treatment of AD.

1-Benzyl-1,2,3,4-tetrahydro-β-carboline as channel blocker of N-methyl-D-aspartate receptors

N-methyl-d-aspartate (NMDA) receptors belong to the family of ligand-gated ion channels and are important for synaptic plasticity and memory function. The NMDA receptor consists of a voltage-dependent channel permeable to Ca(2+) and Na(+) . In Alzheimer's disease, neuronal degeneration is thought to cause an excessive release of glutamate to the extracellular space, which may in turn mediate prolonged stimulation of the NMDA receptor complex and, as a consequence, excessive calcium influx into neuronal cells, leading to subsequent cell death. This process is called glutamate-induced excitotoxicity, and its inhibition may present an effective antidementive therapy. We found that 1-benzyl-1,2,3,4-tetrahydro-β-carboline (1a) blocked NMDA receptor-mediated, glutamate-induced excitotoxicity with an IC(50) value of 27.4 μm, whereas the closely related 1-phenyl-1,2,3,4-tetrahydro-β-carboline (1b) had no effect. The binding modes of the reported compounds were studied by in silico docking simulations. We demonstrate that compounds (S)-1a and (R)-1a, but not (S)-1b and (R)-1b, have the same characteristics of potent NMDA receptor blockers, because they establish the main interactions inside the vestibule region of the receptor described previously for the high-affinity NMDA receptor blocker, MK-801.