2-Carboxytetrahydroquinolines. Conformational and stereochemical requirements for antagonism of the glycine site on the NMDA receptor

Enantioselective Synthesis of 2-Functionalized Tetrahydroquinolines through Biomimetic Reduction

Biomimetic asymmetric reduction of 2-functionalized quinolines has been successfully developed with the chiral and regenerable NAD(P)H model CYNAM in the presence of transfer catalyst simple achiral phosphoric acids, providing the chiral 2-functionalized tetrahydroquinolines with up to 99% ee. Using this methodology as a key step, a chiral and potent opioid analgesic containing a 1,2,3,4-tetrahydroquinoline motif was synthesized with high overall yield.

Does kynurenic acid act on nicotinic receptors? An assessment of the evidence

As a major metabolite of kynurenine in the oxidative metabolism of tryptophan, kynurenic acid is of considerable biological and clinical importance as an endogenous antagonist of glutamate in the central nervous system. It is most active as an antagonist at receptors sensitive to N-methyl-D-aspartate (NMDA) which regulate neuronal excitability and plasticity, brain development and behaviour. It is also thought to play a causative role in hypo-glutamatergic conditions such as schizophrenia, and a protective role in several neurodegenerative disorders, notably Huntington's disease. An additional hypothesis, that kynurenic acid could block nicotinic receptors for acetylcholine in the central nervous system has been proposed as an alternative mechanism of action of kynurenate. However, the evidence for this alternative mechanism is highly controversial, partly because at least eight earlier studies concluded that kynurenic acid blocked NMDA receptors but not nicotinic receptors and five subsequent, independent studies designed to repeat the results have failed to do so. Many studies considered to support the alternative 'nicotinic' hypothesis have been based on the use of analogs of kynurenate such as 7-chloro-kynurenic acid, or putatively nicotinic modulators such as galantamine, but a detailed analysis of the pharmacology of these compounds suggests that the results have often been misinterpreted, especially since the pharmacology of galantamine itself has been disputed. This review examines the evidence in detail, with the conclusion that there is no confirmed, reliable evidence for an antagonist activity of kynurenic acid at nicotinic receptors. Therefore, since there is overwhelming evidence for kynurenate acting at ionotropic glutamate receptors, especially NMDAR glutamate and glycine sites, with some activity at GPR35 sites and Aryl Hydrocarbon Receptors, results with kynurenic acid should be interpreted only in terms of these confirmed sites of action.

Optimization of Bicyclic Lactam Derivatives as NMDA Receptor Antagonists

N-Methyl-d-aspartate (NMDA) receptors are fundamental for the normal function of the central nervous system (CNS), and play an important role in memory and learning. Over-activation of these receptors leads to neuronal loss associated with major neurological disorders such as Parkinson's disease, Alzheimer's disease, schizophrenia, and epilepsy. In this study, 22 novel enantiopure bicyclic lactams were designed, synthesized, and evaluated as NMDA receptor antagonists. Most of the new compounds displayed NMDA receptor antagonism, and the most promising compound showed an IC₅₀ value on the same order of magnitude as that of memantine, an NMDA receptor antagonist in clinical use for the treatment of Alzheimer's disease. Further biological evaluation indicated that this compound is brain permeable (determined by an in vitro assay) and non-hepatotoxic. All these results indicate that (3S,7aS)-7a-(4-chlorophenyl)-3-(4-hydroxybenzyl)tetrahydropyrrolo[2,1-b]oxazol-5(6H)-one (compound 5 b) is a potential candidate for the treatment of pathologies associated with the over-activation of NMDA receptors.

1MeTIQ provides protection against Aβ-induced reduction of surface expression of synaptic proteins and inhibits H₂O₂-induced oxidative stress in primary hippocampal neurons

Alzheimer's disease (AD) is associated with increased brain levels of β-amyloid (Aβ) peptides, which readily self-aggregate into fibrils and oligomers that have particularly deleterious properties toward synapses of excitatory glutamatergic neurons. Here, we examined the neuroprotective effects of 1-methyl-1,2,3,4,-tetrahydroisoquinoline (1MeTIQ) against Aβ-induced loss of synaptic proteins in cultured primary hippocampal neurons. Exposure of mature primary hippocampal neurons to 10 μM synthetic Aβ1-40 over 72 h resulted in ~60 % reduction in the surface expression of NR1 subunit of the NMDA receptor (NMDAR), PSD-95, and synaptophysin, without causing neuronal death. Concomitant treatment with 500 μM of 1MeTIQ, a low-affinity NMDAR antagonist significantly ameliorated the loss of synaptic protein markers. The neuroprotective properties of 1MeTIQ were compared with those of MK-801, which at 0.5 μM concentration also prevented Aβ1-40-induced loss of synaptic proteins in primary neuronal cultures. Furthermore, we provide novel evidence demonstrating effectiveness of 1MeTIQ in reducing the level of reactive oxygen species (ROS) in primary neuronal culture system. As oxidative stress contributes importantly to neurodegeneration in AD, 1MeTIQ may provide a dual neuroproctective effect in AD both as a NMDARs antagonist and ROS formation inhibitor. 1MeTIQ occurs endogenously at low concentrations in the brain and its synthetic form readily penetrates the blood-brain barrier after the systemic administration. Our results highlight a possibility of the application of 1MeTIQ as a neuroprotective agent in AD-related neurodegeneration.

Catalytic Synthesis of Pyrano- and Furoquinolines Using Nano Silica Chromic Acid at Room Temperature

Nano silica chromic acid (nano-SCA) is found to catalyze efficiently the three component-coupling reactions of aldehydes, amines, and cyclic enol ethers such as 3,4-dihydro-2H-pyran and 2,3-dihydrofuran under mild conditions to afford the corresponding pyrano- and furanoquinolines in excellent yields with high endoselectivity. Interestingly, 2,3-dihydrofuran afforded selectively endoproducts under the similar reaction conditions. Heterogeneous reaction conditions, easy procedure, short reaction time, and high yields are some important advantages of this method.

Bismuth(III) salts as synthetic tools in organic transformations

Bismuth is the heaviest stable element of the periodic table and even though it carries the status of heavy metal, it is rated as relatively nontoxic and noncarcinogenic unlike its neighboring elements. Additionally, the fact that it tolerates air and moisture makes the chemistry of bismuth attractive to synthetic chemists. The catalytic nature of this metal is attributed to the capability of its salts to acts as Lewis acids in reactions. The nontoxicity together with the ability to endure moisture makes bismuth compounds favorites of chemists and scientists who are concerned about environmental hazards, and such properties are highly desirable for scale-up of a method. The Lewis acidic nature of salts of this element have been thoroughly investigated in various types of reactions such as cycloaddition reactions, reactions of sugars, protection and deprotection reactions, synthesis of heterocyclic systems etc. Since the 1990s, various research groups have successfully utilized this catalytic nature for many organic transformations. Our group's contribution towards the development of methodologies that are useful in accomplishing various functional group manipulations by making use of the catalytic properties of bismuth salts is portrayed here. The mechanistic aspects and the catalytic efficiency of the bismuth(III) salts are accented together with the synthetic utility and the biological and pharmacological applications of the methodologies developed.

Natural product inspired diversity oriented synthesis of tetrahydroquinoline scaffolds as antitubercular agent

An efficient natural product inspired diversity oriented syn thesis of tetrahydroquinoline analogues has been developed using the natural carbohydrate derived solid acid catalyst via multicomponent aza-Diels-Alder reaction of imine (generated in situ from aromatic amine and aldehyde) with dienophile in acetonitrile in a diastereoselective manner. The use of water as solvent reverses the diastereoselectivity toward the cis isomer. Interestingly, tricyclic pyrano/furano benzopyran with cis diastereoselectivity is obtained when salicylaldehyde is used as an alternative of aromatic aldehyde under the same condition. These synthesized quinolines and benzopyrans analogues have been evaluated for their Antitubercular activity against M. tuberculosis H₃₇Ra, and M. tuberculosis H₃₇Rv, and some of the analogues shows better activity profile than their natural product analogues. The protocol is not only mild, efficient, ecofriendly, but also involves reusable and biodegradable catalyst and provides route for both the diastereoisomer.

Synthesis of substituted 1,2-dihydroquinolines and quinolines from aromatic amines and alkynes by gold(I)-catalyzed tandem hydroamination-hydroarylation under microwave-assisted conditions

A method to efficiently prepare substituted 1,2-dihydroquinolines and quinolines by Au(I)-catalyzed tandem hydroamination-hydroarylation under microwave irradiation was developed. This method requires short reaction time (10-70 min) and has a broad substrate scope.

The first aza Diels-Alder reaction involving an alpha,beta-unsaturated hydrazone as the dienophile: stereoselective synthesis of C-4 functionalized 1,2,3,4-tetrahydroquinolines containing a quaternary stereocenter

The reaction between aromatic imines and methacrolein dimethylhydrazone in the presence of 10% indium trichloride affords in good to excellent yields biologically and synthetically relevant 1,2,3,4-tetrahydroquinolines bearing a hydrazone function at C-4 in a one-pot process that involves the formation of two C-C bonds and the stereoselective generation of two stereocenters, one of them quaternary, and this constitutes the first example of an alpha,beta-unsaturated dimethylhydrazone behaving as a dienophile in a hetero Diels-Alder reaction and the first vinylogous aza-Povarov reaction.

Indole- and indoline-based kainate analogues with antagonist activity at ionotropic glutamate receptors

A conformationally constrained, indole-based kainate analogue was designed based on Gouaux's X-ray structure of kainic acid bound to an iGluR2(S1S2) construct, a structural model for AMPA/kainate ionotropic glutamate receptors. In contrast to the parent kainic acid, a potent agonist, this compound, along with three structurally related analogues derived from synthetic intermediates, exhibited antagonist behavior towards KAR expressed in oocytes, a result that is rationalized by molecular modeling studies.

A Silver-Catalyzed Domino Route toward 1,2-Dihydroquinoline Derivatives from Simple Anilines and Alkynes

[reaction: see text] A silver-catalyzed domino reaction of simple anilines and alkynes generates 1,2-dihydroquinoline derivatives efficiently.

Enantiomerically pure tetrahydroquinoline derivatives as in vivo potent antagonists of the glycine binding site associated to the NMDA receptor

To identify neuroprotective agents after stroke, new substituted tetrahydroquinoline derivatives were designed as antagonists of the glycine binding site associated to the NMDA receptor, satisfying the key pharmacophoric requirements. In particular, the racemate 3c exhibited outstanding in vivo activity in the MCAo model in rats, when given iv both pre- and post-ischemia. Pure enantiomers 3c-(+) and 3c-(-) have been prepared following an original synthetic route. Despite the significant difference of activity observed in vitro, they shown similar neuroprotective profile in the MCAo model in rats.