The importance of synthetic chemistry in the pharmaceutical industry

One-Pot Multicomponent Synthesis and Bioevaluation of Tetrahydroquinoline Derivatives as Potential Antioxidants, α-Amylase Enzyme Inhibitors, Anti-Cancerous and Anti-Inflammatory Agents

Mankind has always suffered from multiple diseases. Therefore, there has been a rigorous need in the field of medicinal chemistry for the design and discovery of new and potent molecular entities. In this work, thirteen tetrahydroquinoline derivatives were synthesized and evaluated biologically for their antioxidant, α-amylase enzyme inhibitory, anti-proliferative and anti-inflammatory activities. SF8 showed the lowest IC50 of 29.19 ± 0.25 µg/mL by scavenging DPPH free radicals. SF5 showed significant antioxidant activity in total antioxidant capacity (TAC) and total reducing power (TRP) assays. SF5 and SF9 showed the maximum inhibition of α-amylase enzyme i.e., 97.47% and 89.93%, respectively, at 200 µg/mL concentration. Five compounds were shortlisted to determine their anti-proliferative potential against Hep-2C cells. The study was conducted for 24, 48 and 72 h. SF8 showed significant results, having an IC50 value of 11.9 ± 1.04 µM at 72 h when compared with standard cisplatin (IC50 value of 14.6 ± 1.01 µM). An in vitro nitric oxide (NO) assay was performed to select compounds for in vivo anti-inflammatory activity evaluation. SF13 scavenged the NO level to a maximum of 85% at 50 µM concentration, followed by SF1 and SF2. Based on the NO scavenging assay results, in vivo anti-inflammatory studies were also performed and the results showed significant activity compared to the standard, acetylsalicylic acid (ASA).

Catalytic Intramolecular Conjugate Additions of Aldehyde-Derived Enamines to α,β-Unsaturated Esters

We report a pairing of known catalysts that enables intramolecular conjugate additions of aldehyde-derived enamines to α,β-unsaturated esters. Despite extensive prior exploration of conjugate additions of aldehyde-derived enamines, catalytic conjugate additions to unactivated enoate esters are unprecedented. Achieving enantioselective and diastereoselective six-membered ring formation requires the coordinated action of a chiral pyrrolidine, for nucleophilic activation of the aldehyde via enamine formation, and a hydrogen bond donor, for electrophilic activation of the enoate ester. Proper selection of the hydrogen bond donor is essential for chemoselectivity, which requires minimizing competition from homoaldol reaction. Utility is demonstrated in a six-step synthesis of (-)-yohimbane from cycloheptene.

A Cascade Reaction of Cinnamyl Azides with Acrylates Directly Generates Tetrahydro-Pyrrolo-Pyrazole Heterocycles

Developing reactions to generate complex and modular building blocks in a concise and direct fashion remains a contemporary synthetic challenge. This work describes a stereoselective cascade reaction between allylic azides and acrylates that directly generates tetrahydro-pyrrolo-pyrazole ring systems. These products contain up to four contiguous stereocenters, two of which may be tetrasubstituted carbon atoms attached to a nitrogen atom. Over 30 examples are provided with an average isolated yield of 71% (ranging from 40% to 94%). The reaction was easily scaled to use more than one gram of starting material, and the products can be readily diversified.

Positional Analogue Scanning: An Effective Strategy for Multiparameter Optimization in Drug Design

Minimizing the number and duration of design cycles needed to optimize hit or lead compounds into high-quality chemical probes or drug candidates is an ongoing challenge in biomedical research. Small structure modifications to hit or lead compounds can have meaningful impacts on pharmacological profiles due to significant effects on molecular and physicochemical properties and intra- and intermolecular interactions. Rapid pharmacological profiling of an efficiently prepared series of positional analogues stemming from the systematic exchange of methine groups with heteroatoms or other substituents in aromatic or heteroaromatic ring-containing hit or lead compounds is one approach toward minimizing design cycles (e.g., exchange of aromatic or heteroaromatic CH groups with N atoms or CF, CMe, or COH groups). In this Perspective, positional analogue scanning is shown to be an effective strategy for multiparameter optimization in drug design, whereby substantial improvements in a variety of pharmacological parameters can be achieved.

One-Pot Selective Saturation and Functionalization of Heteroaromatics Leading to Dihydropyridines and Dihydroquinolines

A one-pot regioselective two C-C-bond-forming dearomatization of pyridines and quinolines is disclosed. Two 3,4-betaines are identified for the first time as very useful organic synthons in heterocyclic chemistry. Furthermore, the chemical reactivity of the prepared trifluoromethyl ketones, a new type of push-pull enones, has been explored to develop straightforward methods for their functionalization. This protocol represents a breakthrough in the dearomatization of heteroaromatics as both the selective saturation and functionalization of heteroaromatics are achieved in high efficiency by the attachment of two substituents, including the valuable trifluoromethyl ketone group.

Vicinal, Double C-H Functionalization of Alcohols via an Imidate Radical-Polar Crossover Cascade

A double functionalization of vicinal sp3 C-H bonds has been developed, wherein a β amine and γ iodide are incorporated onto an aliphatic alcohol in a single operation. This approach is enabled by an imidate radical chaperone, which selectively affords a transient β alkene that is amino-iodinated in situ. Overall, the radical-polar-crossover cascade entails the following key steps: (i) β C-H iodination via 1,5-hydrogen atom transfer (HAT), (ii) desaturation via I2 complexation, and (iii) vicinal amino-iodination of an in situ generated allyl imidate. The synthetic utility of this double C-H functionalization is illustrated by conversion of aliphatic alcohols to a diverse collection of α,β,γ substituted products bearing heteroatoms on three adjacent carbons. The radical-polar crossover mechanism is supported by various experimental probes, including isotopic labeling, intermediate validation, and kinetic studies.

The Medicinal Chemistry in the Era of Machines and Automation: Recent Advances in Continuous Flow Technology

Medicinal chemistry plays a fundamental and underlying role in chemical biology, pharmacology, and medicine to discover safe and efficacious drugs. Small molecule medicinal chemistry relies on iterative learning cycles composed of compound design, synthesis, testing, and data analysis to provide new chemical probes and lead compounds for novel and druggable targets. Using traditional approaches, the time from hypothesis to obtaining the results can be protracted, thus limiting the number of compounds that can be advanced into clinical studies. This challenge can be tackled with the recourse of enabling technologies that are showing great potential in improving the drug discovery process. In this Perspective, we highlight recent developments toward innovative medicinal chemistry strategies based on continuous flow systems coupled with automation and bioassays. After a discussion of the aims and concepts, we describe equipment and representative examples of automated flow systems and end-to-end prototypes realized to expedite medicinal chemistry discovery cycles.

Emerging and inter/trans-disciplinary research areas related to Chemistry

Undoubtedly, Chemistry is a central science because it serves as a support and contributes to the development of many other disciplines, such as biology, geology, physics, paleontology, etc. Just by observing the environment that surrounds us, we can conclude that the world is composed of an infinite number of inert or living components, and all of them are composed of chemical substances of a broad range of complexity. On the other hand, Chemistry has a direct relationship with the economic development of a country, due to most industries are based on chemical processes or materials. The impact of chemistry in different activities is high, in construction, ceramics, and steel, in the food, Energy or Petrochemical industry, in textile design, in Cosmetics and fragrances, in Agrochemicals and fertilizers, Pharmaceutical products, Water treatment, in Companies specialized in Environmental Chemistry, Manufacture of plastics and rubbers, quality and safety processes, in the mining industry, and so forth.

Development of copper-catalyzed enantioselective decarboxylative aldolization for the preparation of perfluorinated 1,3,5-triols featuring supramolecular recognition properties

Fluorine is able to confer unique properties to organic molecules but the scarcity of natural organofluorine sources renders the development of new synthetic methods highly desirable. Using a chiral BOX/Cu combination, enantioselective decarboxylative aldolization of perfluorinated aldehydes has been developed. Most notably, the reaction occurring under mild conditions and with high enantiocontrol can create ketodiols in one single synthetic operation, which are precursors of crucial perfluorinated 1,3,5-triols. In addition, the reaction performed with chloral, validates the proposed transition state model based on steric interactions and provides the first enantioselective synthesis of hexachlorinated ketodiol of great synthetic utility. The ability of perfluorinated 1,3,5-triols to form a central hydrogen-bonding framework allows strong coordination of anions and the chirality obtained through the catalyst-controlled synthetic sequence demonstrates the selective chiral anion recognition ability of polyols.

Metal-free C-C, C-O, C-S and C-N bond formation enabled by SBA-15 supported TFMSA

The construction of intermolecular C-C, C-O, C-S and C-N bonds between diazo compounds and acyclic and cyclic 1,3-dicarbonyl compounds, thiophenol and alkynes was developed by using TFMSA@SBA-15, thus providing a metal-free and eco-friendly platform for forging those chemical bonds.

Palladium-catalysed Heck-type alkenylation reactions in the synthesis of quinolines. Mechanistic insights and recent applications

Recent developments in Pd(0)- and Pd(ii)-catalysed alkenylation reactions for the synthesis of quinolines focusing on mechanistic understanding.

Anticancer Molecule Discovery via C2-Substituent Promoted Oxidative Coupling of Indole and Enolate

C2, C3-disubstituted indole is one of the most frequently encountered motifs in bioactive alkaloids and medicinal chemistry. Thus, developing novel, concise, and efficient access to it is highly desired in drug discovery. Herein, we present such an approach to this scaffold by direct oxidative coupling of C2-substituted indoles and enolates. Compared with indole bearing no C2-substituent, higher yields (up to 96%) were obtained for C2-substituted indoles in most cases. Mechanistic studies showed the reaction went through a Fe-chelated radical-anion oxidative coupling procedure promoted by C2-substituent on indole by two means: (1) stabilizing C2-radical intermediate during the reaction; (2) reducing indole homocoupling. This approach serves as a synthetic useful tool to quickly build up bioactive small molecule library of C2, C3-disubstituted indoles, and several products showed promising anticancer activities. Besides, indomethacin and its analogs were conveniently prepared in three-step sequence efficiently, indicating the potential application of our approach in medicinal chemistry.

Foldamer-templated catalysis of macrocycle formation

Macrocycles, compounds containing a ring of 12 or more atoms, find use in human medicine, fragrances, and biological ion sensing. The efficient preparation of macrocycles is a fundamental challenge in synthetic organic chemistry because the high entropic cost of large-ring closure allows undesired intermolecular reactions to compete. Here, we present a bioinspired strategy for macrocycle formation through carbon-carbon bond formation. The process relies on a catalytic oligomer containing α- and β-amino acid residues to template the ring-closing process. The α/β-peptide foldamer adopts a helical conformation that displays a catalytic primary amine-secondary amine diad in a specific three-dimensional arrangement. This catalyst promotes aldol reactions that form rings containing 14 to 22 atoms. Utility is demonstrated in the synthesis of the natural product robustol.

Electrochemical Synthesis of Hindered Primary and Secondary Amines via Proton-Coupled Electron Transfer

Accessing hindered amines, particularly primary amines α to a fully substituted carbon center, is synthetically challenging. We report an electrochemical method to access such hindered amines starting from benchtop-stable iminium salts and cyanoheteroarenes. A wide variety of substituted heterocycles (pyridine, pyrimidine, pyrazine, purine, azaindole) can be utilized in the cross-coupling reaction, including those substituted with a halide, trifluoromethyl, ester, amide, or ether group, a heterocycle, or an unprotected alcohol or alkyne. Mechanistic insight based on DFT data, as well as cyclic voltammetry and NMR spectroscopy, suggests that a proton-coupled electron-transfer mechanism is operational as part of a hetero-biradical cross-coupling of α-amino radicals and radicals derived from cyanoheteroarenes.

Design of an in vitro biocatalytic cascade for the manufacture of islatravir

Enzyme-catalyzed reactions have begun to transform pharmaceutical manufacturing, offering levels of selectivity and tunability that can dramatically improve chemical synthesis. Combining enzymatic reactions into multistep biocatalytic cascades brings additional benefits. Cascades avoid the waste generated by purification of intermediates. They also allow reactions to be linked together to overcome an unfavorable equilibrium or avoid the accumulation of unstable or inhibitory intermediates. We report an in vitro biocatalytic cascade synthesis of the investigational HIV treatment islatravir. Five enzymes were engineered through directed evolution to act on non-natural substrates. These were combined with four auxiliary enzymes to construct islatravir from simple building blocks in a three-step biocatalytic cascade. The overall synthesis requires fewer than half the number of steps of the previously reported routes.

Theoretical study and experimental validation on the optical emission processes in "free" and "locked" pyrazine derivatives

The excited-state properties of the "free" and "locked" pyrazine derivatives are investigated in solution. DCFP with "free" phenyls is theoretically calculated to be non-emissive due to the non-radiative energy dissipation through strong Duschinsky rotation effect, in agreement with the available experimental result. Surprisingly, DCBP with "bi-locked" phenyls is also calculated to be nonluminous. The emission of DCAP with "conjoined" architecture is predicted to be weaker than DCPP with "single-locked" phenyls, quite contrary to our intuition but further validated by the experimental measurement. The construction of four-, five- and six-membered ring respectively in DCBP, DCAP and DCPP is found to be the major structural origin for the descending relaxation energy in these "locked" systems, thus giving rise to the ascending luminescence order. Our work not only provides strategy for the molecular design of efficient organic light-emitting materials, but also offers valuable insight into the aggregation-induced emission phenomena.

Catalytic Cleavage of C(sp2)-C(sp2) Bonds with Rh-Carbynoids

We report a catalytic strategy that generates rhodium-carbynoids by selective diazo activation of designed carbyne sources. We found that rhodium-carbynoid species provoke C(sp²)-C(sp²) bond scission in alkenes by inserting a monovalent carbon unit between both sp²-hybridized carbons. This skeletal remodeling process accesses synthetically useful allyl cation intermediates that conduct to valuable allylic building blocks upon nucleophile attack. Our results rely on the formation of cyclopropyl-I^(III) intermediates able to undergo electrocyclic ring-opening, following the Woodward-Hoffmann-DePuy rules.

Double-click enables synthesis of chemical libraries for drug discovery

Operationally simple chemical reactions, termed click reactions, are widely used in many scientific fields. A streamlined synthesis of compounds called azides looks set to expand the role of click chemistry still further. See Letter p.86

Catalytic, transannular carbonyl-olefin metathesis reactions

Transannular carbonyl-olefin metathesis reactions complement existing procedures for related ring-closing, ring-opening, and intermolecular carbonyl-olefin metathesis. We herein report the development and mechanistic investigation of FeCl₃-catalyzed transannular carbonyl-olefin metathesis reactions that proceed via a distinct reaction path compared to previously reported ring-closing and ring-opening protocols. Specifically, carbonyl-ene and carbonyl-olefin metathesis reaction pathways are competing under FeCl₃-catalysis to ultimately favor metathesis as the thermodynamic product. Importantly, we show that distinct Lewis acid catalysts are able to distinguish between these pathways to enable the selective formation of either transannular carbonyl-ene or carbonyl-olefin metathesis products. These insights are expected to enable further advances in catalyst design to efficiently differentiate between these two competing reaction paths of carbonyl and olefin functionalities to further expand the synthetic generality of carbonyl-olefin metathesis.

A general strategy for diversifying complex natural products to polycyclic scaffolds with medium-sized rings

The interrogation of complex biological pathways demands diverse small molecule tool compounds, which can often lead to important therapeutics for the treatment of human diseases. Since natural products are the most valuable source for the discovery of therapeutics, the derivatization of natural products has been extensively investigated to generate molecules for biological screenings. However, most previous approaches only modified a limited number of functional groups, which resulted in a limited number of skeleta. Here we show a general strategy for the preparation of a library of complex small molecules by combining state-of-the-art chemistry – the site-selective oxidation of C-H bonds - with reactions that expand rigid, small rings in polycyclic steroids to medium-sized rings. This library occupies a unique chemical space compared to selected diverse reference compounds. The diversification strategy developed herein for steroids can also be expanded to other types of natural products.

Derivatization of natural products is a powerful approach to generate new molecules for biological screenings. Here, the authors employ C-H oxidation and ring expansion methods for the preparation of a library of medium-sized ring skeleta, which occupy a unique chemical space based on chemoinformatic analysis.

Ursolic Acid Derivatives as Potential Agents Against Acanthamoeba Spp

The current chemotherapy of Acanthamoeba keratitis relies on few drugs with low potential and limited efficacy, for all this there is an urgent need to identify new classes of anti-Acanthamoeba agents. In this regard, natural products play an important role in overcoming the current need and medicinal chemistry of natural products represents an attractive approach for the discovery and development of new agents. Ursolic acid, a natural pentacyclic triterpenoid compound, possesses a broad spectrum of activities including anti-Acanthamoeba. Herein, we report on the development by chemical transformation of an ursolic acid-based series of seven compounds (2-8), one of them reported for the first time. The structure-activity relationship (SAR) analysis of their anti-Acanthamoeba activity revealed that acylation/ether formation or oxidation enhances their biological profile, suggesting that the hydrophobic moiety contributes to activity, presumably by increasing the affinity and/or cell membrane permeability. These ursolic acid derivatives highlight the potential of this source as a good base for the development of novel therapeutic agents against Acanthamoeba infections.

BA-12 Inhibits Angiogenesis via Glutathione Metabolism Activation

There is a need for an efficient and low-cost leading compound discovery mode. However, drug development remains slow, expensive, and risky. Here, this manuscript proposes a leading compound discovery strategy based on a combination of traditional Chinese medicine (TCM) formulae and pharmacochemistry, using a ligustrazine-betulinic acid derivative (BA-12) in the treatment of angiogenesis as an example. Blocking angiogenesis to inhibit the growth and metastasis of solid tumors is currently one recognized therapy for cancer in the clinic. Firstly, based on a traditional Prunella vulgaris plaster, BA-12 was synthesized according to our previous study, as it exhibited better antitumor activities than other derivatives on human bladder carcinoma cells (T24); it was then uploaded for target prediction. Secondly, the efficacy and biotoxicity of BA-12 on angiogenesis were evaluated using human umbilical vein endothelial cells (HUVECs), a quail chick chorioallantoic membrane, and Caenorhabditis elegans. According to the prediction results, the main mechanisms of BA-12 were metabolic pathways. Thus, multiple metabolomics approaches were applied to reveal the mechanisms of BA-12. Finally, the predictive mechanisms of BA-12 on glutathione metabolism and glycerophospholipid metabolism activation were validated using targeted metabolomics and pharmacological assays. This strategy may provide a reference for highly efficient drug discovery, with the aim of sharing TCM wisdom for unmet clinical needs.

Quick Building Blocks (QBB): An Innovative and Efficient Business Model To Speed Medicinal Chemistry Analog Synthesis

Many pharmaceutical companies have invested millions of dollars in establishing internal chemical stores to provide reliable access to large numbers of building blocks (BB) for the synthesis of new molecules, especially for the timely design and execution of parallel (library) synthesis. Recognizing budget and logistical limitations, we required a more economically scalable process to provide diverse BB. We disclose a novel business partnership that achieves the goals of just-in-time, economical access to commercial BB that increases chemical space coverage and accelerates the synthesis of new drug candidates. We believe that this model can be of benefit to companies of all sizes that are engaged in drug discovery by reducing cost, increasing diversity of analog molecules in a time-conscious manner, and reducing BB inventory. More efficient use of BB by customers may allow commercial vendors to devote a greater portion of their resources to preparing novel BB that increase chemical diversity as opposed to resynthesizing out-of-stock compounds that are inaccessible within company compound collections.

A Photoredox Coupling Reaction of Benzylboronic Esters and Carbonyl Compounds in Batch and Flow

Mild cross-coupling reaction between benzylboronic esters with carbonyl compounds and some imines was achieved under visible-light-induced iridium-catalyzed photoredox conditions. Functional group tolerance was demonstrated by 51 examples, including 13 heterocyclic compounds. Gram-scale reaction was realized through the use of computer-controlled continuous flow photoreactors.

Late-Stage Functionalization of Platensimycin Leading to Multiple Analogues with Improved Antibacterial Activity in Vitro and in Vivo

Bacterial fatty acid synthases are promising antibacterial targets against multidrug-resistant pathogens. Platensimycin (PTM) is a potent FabB/FabF inhibitor, while its poor pharmacokinetics hampers the clinical development. In this study, a focused library of PTM derivatives was prepared through thiolysis of PTM oxirane (1), followed by various C-C cross-coupling reactions in high yields. Antibacterial screening of these compounds in vitro yielded multiple hits with improved anti-Staphylococcus activities over PTM. Among them, compounds A1, A3, A17, and A28 exhibited improved antibacterial activities over PTM against methicillin-resistant Staphylococcus aureus (MRSA) in a mouse peritonitis model. Compound A28 was further shown to be effective against MRSA infection in a mouse wound model, in comparison to mupirocin. Therefore, the facile preparation and screening of these PTM derivatives, together with their potent antibacterial activities in vivo, suggest a promising strategy to improve the antibacterial activity and pharmacokinetic properties of PTM.

Target 2035: probing the human proteome

Biomedical scientists tend to focus on only a small fraction of the proteins encoded by the human genome despite overwhelming genetic evidence that many understudied proteins are important for human disease. One of the best ways to interrogate the function of a protein and to determine its relevance as a drug target is by using a pharmacological modulator, such as a chemical probe or an antibody. If these tools were available for most human proteins, it should be possible to translate the tremendous advances in genomics into a greater understanding of human health and disease, and catalyze the creation of innovative new medicines. Target 2035 is a global federation for developing and applying new technologies with the goal of creating chemogenomic libraries, chemical probes, and/or functional antibodies for the entire proteome.

Overview of Recent Strategic Advances in Medicinal Chemistry

Introducing novel strategies, concepts, and technologies that speed up drug discovery and the drug development cycle is of great importance both in the highly competitive pharmaceutical industry as well as in academia. This Perspective aims to present a "big-picture" overview of recent strategic innovations in medicinal chemistry and drug discovery.

Brønsted Acid-Catalyzed Formal [2 + 2 + 1] Annulation for the Modular Synthesis of Tetrahydroindoles and Tetrahydrocyclopenta[ b]pyrroles

An expedient synthesis of tetrahydroindoles and tetrahydrocyclopenta[ b]pyrroles, highlighted by Brønsted acid catalyzed formal [2 + 2 + 1] annulation reaction, is reported. Using three readily accessible reaction components, i.e., an electrophilic species in silyloxyallyl cations and two distinct nucleophiles in silylenol ethers and amines, our chemistry enables the assembly and functionalization of these biologically important N-heterocycles in a highly modular manner.

Synthesis of 3-Aryl-3-Sulfanyl Azetidines by Iron-Catalyzed Thiol Alkylation with N-Cbz Azetidinols

New small-ring derivatives can provide valuable motifs in new chemical space for drug design. 3-Aryl-3-sulfanyl azetidines are synthesized directly from azetidine-3-ols in excellent yield by a mild Fe-catalyzed thiol alkylation. A broad range of thiols and azetidinols bearing electron-donating aromatics are successful, proceeding via an azetidine carbocation. The N-carboxybenzyl group is a requirement for good reactivity and enables the NH-azetidine to be revealed. Further reactions of the azetidine sulfides demonstrate their potential for incorporation in drug discovery programs.

Ruthenium-Catalyzed Gram-Scale Preferential C-H Arylation of Tertiary Phosphine

A general protocol for site-preferential mono-C-H arylation of tertiary phosphine ligands catalyzed by a ruthenium(II) complex was devised. This protocol gives access to a series of modified Buchwald-biaryl monophosphines on a gram scale in moderate to excellent yields. A catalytic cycle is proposed derived from knowledge of the intermediates observed by ESI-MS. Importantly, these monoarylated products could be further transformed into dibenzophosphole derivatives.

Catalysis in medicinal chemistry

The advent of transition-metal catalysis (and likewise, bio-catalysis, photoredox-catalysis and organo-catalysis, etc.) promises to greatly increase access to diverse chemical matter in medicinal chemistry, but new catalytic reactions often fail to deliver product in applied synthesis.

Rapid route design of AZD7594

Multidisciplinary collaboration enables the rapid and efficient design and selection of an improved manufacturing route to a new potential medicine for the treatment of asthma.