Development of a Bulk Enabling Route to Maraviroc (UK-427,857), a CCR-5 Receptor Antagonist

Rhodium-Catalyzed Asymmetric Reductive Hydroformylation of α-Substituted Enamides

Chiral γ-amino alcohols are prevalent structural motifs in natural products and bioactive compounds. Nevertheless, efficient and atom-economical synthetic methods toward enantiomerically enriched γ-amino alcohols are still lacking. In this study, a highly enantioselective rhodium-catalyzed reductive hydroformylation of readily available α-substituted enamides is developed, providing a series of pharmaceutically valuable chiral 1,3-amino alcohols in good yields and excellent enantioselectivities in a single step. The development of the 4,4'-bisarylamino-substituted BIBOP ligand is crucial for the success of this transformation. DFT calculations and experimental data have revealed the importance of hydrogen bonding between the N-H group in the structure of TFPNH-BIBOP and the enamide carbonyl group in promoting both high enantioselectivity and reactivity. This method has enabled the concise synthesis of several chiral pharmaceutical intermediates including a single-step synthesis of the key chiral intermediate of maraviroc.

Parallel Minisci Reaction of gem-Difluorocycloalkyl Building Blocks

Parallel Minisci reactions of nonfluorinated and gem-difluorinated C4-C7 cycloalkyl building blocks (trifluoroborates and carboxylic acids) with a series of electron-deficient heterocycles were studied. A comparison of the reaction's outcome revealed better product yields in the case of carboxylic acids as the radical precursors in most cases, albeit these reagents were used with three-fold excess under optimized conditions. The nature of the heterocyclic core was found to be important for successful incorporation of the cycloalkyl fragment. The impact of the CF2 moiety on the oxidation potential of fluorinated cycloalkyl trifluoroborates and the reaction outcome, in general, was also evaluated.

Development of Catalytic Enantioselective Mannich Reactions Using Esters

Catalytic enantioselective Mannich reactions of simple nonactivated esters proceeded using a chiral potassium strong base catalyst prepared from a chiral bisoxazoline and potassium hexamethyldisilazide. Alkyl acetates, alkyl propionates, and an alkyl butyrate were employed as the simple esters, and the desired reactions proceeded smoothly to afford Mannich products in good to high yields with high enantioselectivities. One of the products was successfully employed in the asymmetric total synthesis of Maraviroc.

Review on fluorinated nucleoside/non-nucleoside FDA-approved antiviral drugs

FDA-approved antiviral agents represent an important class that has attracted attention in recent years to combat current and future threats of viral pandemics. Fluorine ameliorates the electronic, lipophilic and steric problems of drugs. Additionally, fluorine can prolong drug activity and improve metabolic stability, thereby, modifying their pharmacodynamic and pharmacokinetic character. Herein, we summarized the fluorinated FDA-approved antiviral agents, dealing with biological aspects, mechanisms of action, and synthetic pathways.

Metal-free synthesis of 3-trifluoromethyl-1,2,4-triazoles via multi-component reaction of trifluoroacetimidoyl chlorides, hydrazine hydrate and benzene-1,3,5-triyl triformate

A convenient approach for the construction of pharmaceutically valuable 3-trifluoromethyl-1,2,4-triazoles has been developed, which employs the readily available trifluoroacetimidoyl chlorides, hydrazine hydrate and benzene-1,3,5-triyl triformate (TFBen) as starting materials. The multi-component reaction features broad substrate scope, high efficiency, and scalability, providing a facile and straightforward route to the biologically important 3-trifluoromethyl-1,2,4-triazole scaffolds in moderate to good yields. Considering its broad-spectrum pharmaceutical activity, the method offers the opportunity for the further study towards the toxicity risk assessment and structure-activity relationship of the pharmaceuticals containing trifluoromethyl-1,2,4-triazole cores.

Synergistic Catalysis between a Dipeptide Phosphonium Salt and a Metal-Based Lewis Acid for Asymmetric Synthesis of N-Bridged [3.2.1] Ring Systems

We present an unprecedented synergic catalytic route for the asymmetric construction of fluorinated N-bridged [3.2.1] cyclic members of tropane family via a bifunctional phosphonium salt/silver co-catalyzed cyclization process. A broad variety of substrates bearing an assortment of functional groups are compatible with this method, providing targeted compounds bearing seven-membered ring and four contiguous stereocenters in high yields with excellent stereoselectivities. The gram-scale preparations, facile elaborations and preliminary biological activities of the products demonstrate the application potential. Moreover, both experimental and computational mechanistic studies revealed that the cyclization proceeded via a "sandwich" reaction model with multiple weak-bond cooperative activations. Insights gained from our studies are expected to advance general efforts towards the catalytic synthesis of challenging chiral heterocyclic molecules.

A concise method for cyclic gem-difluoroacyl scaffolds via visible-light-mediated redox-neutral cascade radical cyclization of alkenes

A series of diverse alkenes were engaged in redox-neutral radical tandem cyclization initiated by a CF2 radical precursor via visible-light-induced photocatalysis, affording various cyclic gem-difluoroacyl arenes in good to excellent yields.

Photochemical C-F Activation Enables Defluorinative Alkylation of Trifluoroacetates and -Acetamides

The installation of gem-difluoromethylene groups into organic structures remains a daunting synthetic challenge despite their attractive structural, physical, and biochemical properties. A very efficient retrosynthetic approach would be the functionalization of a single C-F bond from a trifluoromethyl group. Recent advances in this line of attack have enabled the C-F activation of trifluoromethylarenes, but limit the accessible motifs to only benzylic gem-difluorinated scaffolds. In contrast, the C-F activation of trifluoroacetates would enable their use as a bifunctional gem-difluoromethylene synthon. Herein, we report a photochemically mediated method for the defluorinative alkylation of a commodity feedstock: ethyl trifluoroacetate. A novel mechanistic approach was identified using our previously developed diaryl ketone HAT catalyst to enable the hydroalkylation of a diverse suite of alkenes. Furthermore, electrochemical studies revealed that more challenging radical precursors, namely trifluoroacetamides, could also be functionalized via synergistic Lewis acid/photochemical activation. Finally, this method enabled a concise synthetic approach to novel gem-difluoro analogs of FDA-approved pharmaceutical compounds.

Structure-Based Design and Development of Chemical Probes Targeting Putative MOR-CCR5 Heterodimers to Inhibit Opioid Exacerbated HIV-1 Infectivity

Crystal structures of ligand-bound G-protein-coupled receptors provide tangible templates for rationally designing molecular probes. Herein, we report the structure-based design, chemical synthesis, and biological investigations of bivalent ligands targeting putative mu opioid receptor C-C motif chemokine ligand 5 (MOR-CCR5) heterodimers. The bivalent ligand VZMC013 possessed nanomolar level binding affinities for both the MOR and CCR5, inhibited CCL5-stimulated calcium mobilization, and remarkably improved anti-HIV-1BaL activity over previously reported bivalent ligands. VZMC013 inhibited viral infection in TZM-bl cells coexpressing CCR5 and MOR to a greater degree than cells expressing CCR5 alone. Furthermore, VZMC013 blocked human immunodeficiency virus (HIV)-1 entry in peripheral blood mononuclear cells (PBMC) cells in a concentration-dependent manner and inhibited opioid-accelerated HIV-1 entry more effectively in phytohemagglutinin-stimulated PBMC cells than in the absence of opioids. A three-dimensional molecular model of VZMC013 binding to the MOR-CCR5 heterodimer complex is constructed to elucidate its mechanism of action. VZMC013 is a potent chemical probe targeting MOR-CCR5 heterodimers and may serve as a pharmacological agent to inhibit opioid-exacerbated HIV-1 entry.

Biocatalytic routes to anti-viral agents and their synthetic intermediates

An assessment of biocatalytic strategies for the synthesis of anti-viral agents, offering guidelines for the development of sustainable production methods for a future COVID-19 remedy.

A practical catalytic reductive amination of carboxylic acids

We report reductive alkylation reactions of amines using carboxylic acids as nominal electrophiles. The two-step reaction exploits the dual reactivity of phenylsilane and involves a silane-mediated amidation followed by a Zn(OAc)2-catalyzed amide reduction. The reaction is applicable to a wide range of amines and carboxylic acids and has been demonstrated on a large scale (305 mmol of amine). The rate differential between the reduction of tertiary and secondary amide intermediates is exemplified in a convergent synthesis of the antiretroviral medicine maraviroc. Mechanistic studies demonstrate that a residual 0.5 equivalents of carboxylic acid from the amidation step is responsible for the generation of silane reductants with augmented reactivity, which allow secondary amides, previously unreactive in zinc/phenylsilane systems, to be reduced.

Tailor-Made Amino Acids and Fluorinated Motifs as Prominent Traits in Modern Pharmaceuticals

Structural analysis of modern pharmaceutical practices allows for the identification of two rapidly growing trends: the introduction of tailor-made amino acids and the exploitation of fluorinated motifs. Curiously, the former represents one of the most ubiquitous classes of naturally occurring compounds, whereas the latter is the most xenobiotic and comprised virtually entirely of man-made derivatives. Herein, 39 selected compounds, featuring both of these traits in the same molecule, are profiled. The total synthesis, source of the corresponding amino acids and fluorinated residues, and medicinal chemistry aspects and biological properties of the molecules are discussed.

Iridium-catalysed C–H borylation of β-aryl-aminopropionic acids

Iridium-catalysed C–H borylation of β-aryl-aminopropionic acid derivatives gives 3,5-functionalised protected β-aryl-aminopropionic acid boronates. One-pot borylation–functionalisation provides diverse building blocks for medicinal chemistry.

Screening and Comparative Characterization of Microorganisms from Iranian Soil Samples Showing ω-Transaminase Activity toward a Plethora of Substrates

In this study, soil microorganisms from Iran were screened for ω-transaminase (ω-TA) activity based on growth on minimal media containing (rac)-α-methylbenzylamine (rac-α-MBA) as a sole nitrogen source. Then, for the selection of strains with high enzyme activity, a colorimetric o-xylylendiamine assay was conducted. The most promising strains were identified by 16S rDNA sequencing. Five microorganisms showing high ω-TA activity were subjected to determine optimal conditions for ω-TA activity, including pH, temperature, co-solvent, and the specificity of the ω-TA toward different amine donors and acceptors. Among the five screened microorganisms, Bacillus halotolerans turned out to be the most promising strain: Its cell-free extract showed a highly versatile amino donor spectrum toward aliphatic, aromatic chiral amines and a broad range of pH activity. Transaminase activity also exhibited excellent solvent tolerance, with maximum turnover in the presence of 30% (v/v) DMSO.

Reductive Amination in the Synthesis of Pharmaceuticals

Reductive amination plays a paramount role in pharmaceutical and medicinal chemistry owing to its synthetic merits and the ubiquitous presence of amines among biologically active compounds. It is one of the key approaches to C-N bond construction due to its operational easiness and a wide toolbox of protocols. Recent studies show that at least a quarter of C-N bond-forming reactions in the pharmaceutical industry are performed via reductive amination. This Review concisely compiles information on 71 medical substances that are synthesized by reductive amination. Compounds are grouped according to the principle of action, which includes drugs affecting the central nervous system, drugs affecting the cardiovascular system, anticancer drugs, antibiotics, antiviral and antifungal medicines, drugs affecting the urinary system, drugs affecting the respiratory system, antidiabetic medications, drugs affecting the gastrointestinal tract, and drugs regulating metabolic processes. A general synthetic scheme is provided for each compound, and the description is focused on reductive amination steps. The green chemistry metric of reaction mass efficiency was calculated for all reactions.

An approach to highly efficient reduction of β-enamino esters: A convenient synthesis of β-amino esters

Chemoselective reduction of β-enamino esters with NaBH(OAc)3promoted by MgI2etherate affords the corresponding β-amino esters in excellent yields in a short time under mild conditions.

A Practical Electrophilic Nitrogen Source for the Synthesis of Chiral Primary Amines by Copper-Catalyzed Hydroamination

A mild and practical method for the catalytic installation of the amino group across alkenes and alkynes has long been recognized as a significant challenge in synthetic chemistry. As the direct hydroamination of olefins using ammonia requires harsh conditions, the development of suitable electrophilic aminating reagents for formal hydroamination methods is of importance. Herein, we describe the use of 1,2-benzisoxazole as a practical electrophilic primary amine source. Using this heterocycle as a new amino group delivery agent, a mild and general protocol for the copper-hydride-catalyzed hydroamination of alkenes and alkynes to form primary amines was developed. This method provides access to a broad range of chiral α-branched primary amines and linear primary amines, as demonstrated by the efficient synthesis of the antiretroviral drug maraviroc and the formal synthesis of several other pharmaceutical agents.

The Chemical Synthesis and Applications of Tropane Alkaloids

Tropanes are an important class of alkaloid natural products that are found in plants all over the world. These compounds can exhibit significant biological activity and are among the oldest known medicines. In the early 19th century, tropanes were isolated, characterized, and synthesized by notable chemical researchers. Their significant biological activities have inspired tremendous research efforts toward their synthesis and the elucidation of their pharmacological activity both in academia and in industry. In this chapter, which addresses the developments in this field since 1994, the focus is on the synthesis of these compounds, and several examples of sophisticated synthetic protocols involving both asymmetric and catalytic approaches are described. In addition, the structures of more than 100 new alkaloids are included as well as the applications and pharmacological properties of some tropane alkaloids.

[3 + 2] Cycloaddition of Nitrile Ylides with Diazonium Salts: Copper-Catalyzed One-Pot Synthesis of Fully Substituted 1,2,4-Triazoles

A novel [3 + 2] cycloaddition between nitrile ylides and diazonium salts was well-established. This copper-catalyzed three-component reaction was distinguished by mild conditions, ready availability, and operational simplicity, thus opening access to 1,2,4-triazoles with a diverse set of substitution patterns.

Asymmetric Mannich Reaction and Construction of Axially Chiral Sulfone-Containing Styrenes in One Pot from α-Amido Sulfones Based on the Waste-Reuse Strategy

A simultaneous asymmetric Mannich reaction and the construction of axially chiral sulfone-containing styrenes in one pot from α-amido sulfones based on the waste-reuse strategy was demonstrated. A series of chiral β-amino diesters and axially chiral sulfone-containing styrenes with various functional groups were synthesized in good to excellent yields and enantioselectivities under mild conditions. In addition, this protocol has been successfully applied to synthesize the anti-HIV drug Maraviroc and chiral trichloro derivatives.

Bifunctional Chimera That Coordinately Targets Human Immunodeficiency Virus 1 Envelope gp120 and the Host-Cell CCR5 Coreceptor at the Virus-Cell Interface

To address the urgent need for new agents to reduce the global occurrence and spread of AIDS, we investigated the underlying hypothesis that antagonists of the HIV-1 envelope (Env) gp120 protein and the host-cell coreceptor (CoR) protein can be covalently joined into bifunctional synergistic combinations with improved antiviral capabilities. A synthetic protocol was established to covalently combine a CCR5 small-molecule antagonist and a gp120 peptide triazole antagonist to form the bifunctional chimera. Importantly, the chimeric inhibitor preserved the specific targeting properties of the two separate chimera components and, at the same time, exhibited low to subnanomolar potencies in inhibiting cell infection by different pseudoviruses, which were substantially greater than those of a noncovalent mixture of the individual components. The results demonstrate that targeting the virus-cell interface with a single molecule can result in improved potencies and also the introduction of new phenotypes to the chimeric inhibitor, such as the irreversible inactivation of HIV-1.

The Hitchhiker's Guide to Flow Chemistry ∥

Flow chemistry involves the use of channels or tubing to conduct a reaction in a continuous stream rather than in a flask. Flow equipment provides chemists with unique control over reaction parameters enhancing reactivity or in some cases enabling new reactions. This relatively young technology has received a remarkable amount of attention in the past decade with many reports on what can be done in flow. Until recently, however, the question, "Should we do this in flow?" has merely been an afterthought. This review introduces readers to the basic principles and fundamentals of flow chemistry and critically discusses recent flow chemistry accounts.

Diazabicyclo analogues of maraviroc: synthesis, modeling, NMR studies and antiviral activity

Two diazabicyclo analogues of maraviroc, in which the azabicyclooctane moiety is replaced by diazabicyclooctane or diazabicyclononane, were synthesized and tested, through a viral neutralization assay, on a panel of six pseudoviruses. The diazabicyclooctane derivative maintained a significant infectivity reduction power, whereas the diazabicyclononane was less effective. Biological data were rationalized through a computational study that allowed the conformational preferences of the compounds to be determined and a correlation between the inhibitory activity, the bridge length of the bicycle, and the rotational barrier around dihedral angle τ7 to be hypothesized. A high-field NMR analysis supported the modeling results.

Exploration of bivalent ligands targeting putative mu opioid receptor and chemokine receptor CCR5 dimerization

Modern antiretroviral therapies have provided HIV-1 infected patients longer lifespans and better quality of life. However, several neurological complications are now being seen in these patients due to HIV-1 associated injury of neurons by infected microglia and astrocytes. In addition, these effects can be further exacerbated with opiate use and abuse. One possible mechanism for such potentiation effects of opiates is the interaction of the mu opioid receptor (MOR) with the chemokine receptor CCR5 (CCR5), a known HIV-1 co-receptor, to form MOR-CCR5 heterodimer. In an attempt to understand this putative interaction and its relevance to neuroAIDS, we designed and synthesized a series of bivalent ligands targeting the putative CCR5-MOR heterodimer. To understand how these bivalent ligands may interact with the heterodimer, biological studies including calcium mobilization inhibition, binding affinity, HIV-1 invasion, and cell fusion assays were applied. In particular, HIV-1 infection assays using human peripheral blood mononuclear cells, macrophages, and astrocytes revealed a notable synergy in activity for one particular bivalent ligand. Further, a molecular model of the putative CCR5-MOR heterodimer was constructed, docked with the bivalent ligand, and molecular dynamics simulations of the complex was performed in a membrane-water system to help understand the biological observation.