Synthesis and structure–activity relationships of selective norepinephrine reuptake inhibitors (sNRI) with a heterocyclic ring constraint

Dinuclear Zn-Catalytic System as Brønsted Base and Lewis Acid for Enantioselectivity in Same Chiral Environment

Zinc (Zn) is a crucial element with remarkable significance in organic transformations. The profusion of harmless zinc salts in the Earth's outer layer qualifies zinc as a noteworthy contender for inexpensive and eco-friendly reagents and catalysts. Recently, widely recognized uses of organo-Zn compounds in the field of organic synthesis have undergone extensive expansion toward asymmetric transformations. The ProPhenol ligand, a member of the chiral nitrogenous-crown family, exhibits the spontaneous formation of a dual-metal complex when reacted with alkyl metal (R-M) reagents, e.g., ZnEt2. The afforded Zn complex possesses two active sites, one Lewis acid and the other Brønsted base, thereby facilitating the activation of nucleophiles and electrophiles simultaneously within the same chiral pocket. In this comprehensive analysis, we provide a thorough account of the advancement and synthetic potential of these diverse catalysts in organic synthesis, while emphasizing the reactivity and selectivities, i.e., dr and ee due to the design/structure of the ligands employed.

Rh-Catalyzed Sequential Asymmetric Hydrogenations of 3-Amino-4-Chromones Via an Unusual Dynamic Kinetic Resolution Process

Rh-catalyzed sequential asymmetric hydrogenations of 3-amino-4-chromones have been achieved for the first time via an unprecedented dynamic kinetic resolution under neutral conditions, providing (S,R)-3-amino-4-chromanols in high yields (up to 98%) with excellent enantio- and diastereoselectivities (up to 99.9% ee and 20:1 dr). The mechanistic studies based on control experiments and density functional theory (DFT) calculations suggest that the dynamic kinetic resolution process for the intermediate enantiomers generated in the first hydrogenation step proceeded via a stereomutation (or called chiral assimilation) pathway from an undesired enantiomer to the desired enantiomer rather than via traditional racemization of the undesired enantiomer. The protocol can be performed on a gram scale with a relatively low catalyst loading and offers a practical and convenient pathway for synthesizing a series of bioactive chromanols and their derivatives.

Biocatalytic asymmetric synthesis of (R)-1-tetralol using Lactobacillus paracasei BD101

Asymmetric bioreduction of ketones is a fundamental process in the production of organic molecules. Compounds containing tetralone rings are found in the structure of many biologically active and pharmaceutical molecules. Biocatalytic reduction of ketones is one of the most promising and significant routes to prepare optically active alcohols. In this study, the reductive capacity of Lactobacillus paracasei BD101 was investigated as whole-cell biocatalyst in the enantioselective reduction of 1-tetralone (1). In biocatalytic reduction reactions, the conversion of the substrate and the enantiomeric excess (ee) of the product are significantly affected by optimization parameters such as temperature, agitation rate, pH, and incubation time. Effects of these parameters on ee and conversion were investigated comprehensively. (R)-1-tetralol ((R)-2), which can be used to treat disorder such as obsessive compulsive, post-traumatic stress, premenstrual dysphoric, and social anxiety, was manufactured in enantiopure form, high yield and gram-scale, using whole-cell biocatalysts of L. paracasei BD101. The 7.04 g of (R)-2 was obtained in optically pure form with 95% yield. Also, to our knowledge, this is the first report on production of (R)-2 using whole-cell biocatalyst in excellent yield, conversion, enantiopure form and gram scale. This is a clean, eco-friendly and cheap method for the synthesis of (R)-2 compared with chemical catalyst.

Synthesis of 2-alkyl-chroman-4-ones via cascade alkylation-dechlorination of 3-chlorochromones

An efficient and mild synthetic approach for 2-alkyl-substituted chroman-4-ones via zinc-mediated cascade decarboxylative β-alkylation and dechlorination of 3-chlorochromones was developed. This transformation employed commercially available starting materials and was performed under mild conditions without heat, visible light, peroxide or heavy metals. Moreover, various alkyl NHPI esters with functional groups and differently substituted 3-chlorochromones were tolerated, affording the targeted products with moderate to excellent yields. This protocol could be utilized to construct a diverse library of 2-substituted chroman-4-one derivatives, which could be useful in the discovery of lead compounds for drug discovery in the future.

Dinuclear zinc synergistic catalytic asymmetric phospha-Michael/Michael cascade reaction: synthesis of 1,2,3-trisubstituted indanes bearing phosphoryl groups

A new dinuclear zinc synergistic catalytic asymmetric phospha-Michael/Michael cascade reaction of o-dienones and dialkyl phosphates is reported. This method has been proven to be general and efficient for the formation of a range of chiral 1,2,3-trisubstituted indane compounds containing phosphorus groups in good yields (up to 92%) with excellent stereoselectivities (up to >99% ee and up to >99 : 1 dr). The relative configuration of the product was identified as having a trans,trans substitution pattern via two-dimensional (2D) nuclear Overhauser effect spectroscopy 1H-1H NMR experiments. A possible mechanism was proposed.

A rhodium-catalyzed tandem reaction of N-sulfonyl triazoles with indoles: access to indole-substituted indanones

Rhodium(ii)-catalyzed tandem reaction of N-sulfonyl triazoles with indoles delivered structurally diverse indole-substituted indanones bearing vicinal quaternary carbon centers.

An S(N)Ar approach to sterically hindered ortho-alkoxybenzaldehydes for the synthesis of olefin metathesis catalysts

A three-step procedure has been developed for preparing ortho-alkoxybenzaldehydes from ortho-fluorobenzaldehydes that tolerates the use of sterically hindered sodium alkoxide nucleophiles. The protocol is modular and operationally convenient. The ortho-alkoxybenzaldehyde products can be converted in one additional step to ortho-alkoxystyrenes by a Wittig reaction. These styrenes are precursors to the chelating benzylidene moiety in a proposed series of novel ruthenium complexes for use in olefin metathesis. Chelation with three representative styrenes has been demonstrated.

Highly stereoselective synthesis of 1,2,3-trisubstituted indanes via oxidative N-heterocyclic carbene-catalyzed cascades

Three stereocenters are formed in the carbene catalyzed cascade reaction of enals with various β-diketones to give the corresponding indane derivatives with excellent stereoselectivities. The products are readily transformed to the corresponding 1,2,3-trisubstituted indane derivatives, which represent privileged substructures in medicinal chemistry.

Silylation-based kinetic resolution of monofunctional secondary alcohols

The nucleophilic small molecule catalyst (-)-tetramisole was found to catalyze the kinetic resolution of monofunctional secondary alcohols via enantioselective silylation. Optimization of this new methodology allows for selectivity factors up to 25 utilizing commercially available reagents and mild reaction conditions.

1-(Indolin-1-yl)-1-phenyl-3-propan-2-olamines as potent and selective norepinephrine reuptake inhibitors

Efforts to identify new selective and potent norepinephrine reuptake inhibitors (NRIs) for multiple indications by structural modification of the previous 3-(arylamino)-3-phenylpropan-2-olamine scaffold led to the discovery of a novel series of 1-(indolin-1-yl)-1-phenyl-3-propan-2-olamines (9). Investigation of the structure-activity relationships revealed that small alkyl substitution at the C3 position of the indoline ring enhanced selectivity for the norepinephrine transporter (NET) over the serotonin transporter (SERT). Several compounds bearing a 3,3-dimethyl group on the indoline ring, 9k, 9o,p, and 9s,t, exhibited potent inhibition of NET (IC(50) = 2.7-6.5 nM) and excellent selectivity over both serotonin and dopamine transporters. The best example from this series, 9p, a potent and highly selective NRI, displayed oral efficacy in a telemetric rat model of ovariectomized-induced thermoregulatory dysfunction, a mouse p-phenylquinone (PPQ) model of acute visceral pain, and a rat spinal nerve ligation (SNL) model of neuropathic pain.

Structure-activity relationships of norepinephrine reuptake inhibitors with benzothiadiazine dioxide or dihydrosulfostyril cores

Two related series of selective norepinephrine reuptake inhibitors were synthesized based on 3,4-dihydro-1H-2,1,3-benzothiadiazine 2,2-dioxide or 3,4-dihydrosulfostyril cores, and screened for monoamine reuptake inhibition. Structure-activity relationships were determined for the series' in vitro potency and selectivity versus serotonin or dopamine transporter inhibition, and analogs based on both cores were identified as potent and selective NRIs. The 3,4-dihydrosulfostyril series was further tested for microsome stability, and compound 16j, which was optimized for both potency and stability, showed efficacy in an in vivo model of thermoregulatory dysfunction.

Diastereoselective synthesis of indanes via a domino Stetter-Michael reaction

N-Heterocyclic carbenes were found to catalyze a domino Stetter-Michael reaction for the synthesis of indanes. The products were obtained in good yield and diastereomeric ratio, allowing access to highly functionalized indanes under mild conditions. In addition, the functional groups present on the indanes could be used for the synthesis of polycyclic pyrroles.

Recent advances in the understanding of the interaction of antidepressant drugs with serotonin and norepinephrine transporters

The biogenic monoamine transporters are integral membrane proteins that perform active transport of extracellular dopamine, serotonin and norepinephrine into cells. These transporters are targets for therapeutic agents such as antidepressants, as well as addictive substances such as cocaine and amphetamine. Seminal advances in the understanding of the structure and function of this transporter family have recently been accomplished by structural studies of a bacterial transporter, as well as medicinal chemistry and pharmacological studies of mammalian transporters. This feature article focuses on antidepressant drugs that act on the serotonin and/or the norepinephrine transporters. Specifically, we focus on structure-activity relationships of these drugs with emphasis on relationships between their molecular properties and the current knowledge of transporter structure.