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Methods for residue-selective and stable modification of canonical amino acids enable the installation of distinct functionality which can aid in the interrogation of biological processes or the generation of new therapeutic modalities. Herein, we report an extensive investigation of reactivity and stability profiles for a series of vinylheteroarene motifs. Studies on small molecule and protein substrates identified an optimum vinylheteroarene scaffold for selective cysteine modification. Utilisation of this lead linker to modify a number of protein substrates with various functionalities, including the synthesis of a homogeneous, stable and biologically active antibody–drug conjugate (ADC) was then achieved. The reagent was also efficient in labelling proteome-wide cysteines in cell lysates. The efficiency and selectivity of these reagents as well as the stability of the products makes them suitable for the generation of biotherapeutics or studies in chemical biology., Vinylheteroarene linkers can chemoselectively modify cysteine residues in proteins and antibodies. These linkers give stable bioconjugates, and were used to synthesise efficacious antibody-drug conjugates.

Correction for ‘A general approach for the site-selective modification of native proteins, enabling the generation of stable and functional antibody–drug conjugates’ by Stephen J. Walsh et al., Chem. Sci., 2019, DOI: 10.1039/c8sc04645j.

Computational binding free energy predictions were validated against experiment and used to design new inhibitors of an important protein–protein interaction., Free energy perturbation theory, in combination with enhanced sampling of protein–ligand binding modes, is evaluated in the context of fragment-based drug design, and used to design two new small-molecule inhibitors of the Aurora A kinase–TPX2 protein–protein interaction.

Using N-sulfonyl triazoles and oxetanes, a large variety of heterocycles and macrocycles were prepared via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations., Using N-sulfonyl triazoles as substrates, compounds as diverse as 2-imino tetrahydrofurans, 13- and 15-membered ring aza-macrocycles can be prepared selectively via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations of α-imino carbenes and oxetanes under Rh(ii)-catalysis or thermal activation. Spirocyclic N-heterocycles are also accessible by means of Buchwald–Hartwig and Pictet–Spengler cyclizations. By reaction control, substrate selection or further derivatization, a large variety of chemical structures is thus achievable. Finally, using triazoles reacting under thermal activation, interesting mechanistic insight was obtained.

The development of site-specific modification of alkyne-functionalized proteins using dimethylarylsilanes and substoichiometric or low-loading of Ru(ii) catalysts is reported. Furthermore, the resultant gem-vinylsilane can undergo further targeted chemical modifications, highlighting its potential for single-site, dual-modification applications., Transition metal catalysis has emerged as a powerful strategy to expand synthetic flexibility of protein modification. Herein, we report a cationic Ru(ii) system that enables the first example of alkyne hydrosilylation between dimethylarylsilanes and O-propargyl-functionalized proteins using a substoichiometric amount or low-loading of Ru(ii) catalyst to achieve the first C–Si bond formation on full-length substrates. The reaction proceeds under physiological conditions at a rate comparable to other widely used bioorthogonal reactions. Moreover, the resultant gem-disubstituted vinylsilane linkage can be further elaborated through thiol–ene coupling or fluoride-induced protodesilylation, demonstrating its utility in further rounds of targeted modifications.

We describe stereocontrolled semi-syntheses of deguelin and tephrosin, anti-cancer rotenoids isolated from Tephrosia vogelii., We describe stereocontrolled semi-syntheses of deguelin and tephrosin, anti-cancer rotenoids isolated from Tephrosia vogelii. Firstly, we present a new two-step transformation of rotenone into rot-2′-enonic acid via a zinc-mediated ring opening of rotenone hydrobromide. Secondly, following conversion of rot-2′-enonic acid into deguelin, a chromium-mediated hydroxylation provides tephrosin as a single diastereoisomer. An Étard-like reaction mechanism is proposed to account for the stereochemical outcome. Our syntheses of deguelin and tephrosin are operationally simple, scalable and high yielding, offering considerable advantages over previous methods.

Novel divergent methodology to access sp3-rich spirocyclic fragments is reported. First, a robust modular synthesis of bis-alkene amino ester building blocks was developed. Three different carbocyc...

The synthesis of a previously undescribed sp3-rich 6-5-5-6 tetracyclic ring scaffold using a palladium catalysed domino Heck–Suzuki reaction is reported., The synthesis of a previously undescribed sp3-rich 6-5-5-6 tetracyclic ring scaffold using a palladium catalysed domino Heck–Suzuki reaction is reported. This reaction is high-yielding, selective for the domino process over the direct Suzuki reaction and tolerant towards a variety of boronic acids. The novel scaffold can also be accessed via domino Heck–Stille and radical cyclisations. Compounds based around this scaffold were found to be effective antimitotic agents in a human cancer cell line. Detailed phenotypic profiling showed that the compounds affected the congression of chromosomes to give mitotic arrest and apoptotic cell death. Thus, a novel structural class of antimitotic agents that does not disrupt the tubulin network has been identified.

Protein kinases are a large class of enzymes with numerous biological roles and many have been implicated in a vast array of diseases, including cancer and the novel coronavirus infection COVID-19. Thus, the development of chemical probes to selectively target each kinase is of great interest. Inhibition of protein kinases with ATP-competitive inhibitors has historically been the most widely used method. However, due to the highly conserved structures of ATP-sites, the identification of truly selective chemical probes is challenging. In this review, we use the Ser/Thr kinase CK2 as an example to highlight the historical challenges in effective and selective chemical probe development, alongside recent advances in the field and alternative strategies aiming to overcome these problems. The methods utilised for CK2 can be applied to an array of protein kinases to aid in the discovery of chemical probes to further understand each kinase’s biology, with wide-reaching implications for drug development.

Pseudomonas aeruginosa is an opportunistic pathogen responsible for many hospital-acquired infections. P. aeruginosa can thrive in diverse infection scenarios by rewiring its central metabolism. An example of this is the production of biomass from C2 nutrient sources such as acetate via the glyoxylate shunt when glucose is not available. The glyoxylate shunt is comprised of two enzymes, isocitrate lyase (ICL) and malate synthase G (MS), and flux through the shunt is essential for the survival of the organism in mammalian systems. In this study, we characterized the mode of action and cytotoxicity of structural analogs of 2-aminopyridines, which have been identified by earlier work as being inhibitory to both shunt enzymes. Two of these analogs were able to inhibit ICL and MS in vitro and prevented growth of P. aeruginosa on acetate (indicating cell permeability). Moreover, the compounds exerted negligible cytotoxicity against three human cell lines and showed promising in vitro drug metabolism and safety profiles. Isothermal titration calorimetry was used to confirm binding of one of the analogs to ICL and MS, and the mode of enzyme inhibition was determined. Our data suggest that these 2-aminopyridine analogs have potential as anti-pseudomonal agents.

Hemiasterlin is an antimitotic marine natural product with reported sub‐nanomolar potency against several cancer cell lines. Herein, we describe an expeditious total synthesis of hemiasterlin featuring a four‐component Ugi reaction (Ugi‐4CR) as the key step. The convergent synthetic strategy enabled rapid access to taltobulin (HTI‐286), a similarly potent synthetic analogue. This short synthetic sequence enabled investigation of both hemiasterlin and taltobulin as cytotoxic payloads in antibody–drug conjugates (ADCs). These novel ADCs displayed sub‐nanomolar cytotoxicity against HER2‐expressing cancer cells, while showing no activity against antigen‐negative cells. This study demonstrates an improved synthetic route to a highly valuable natural product, facilitating further investigation of hemiasterlin and its analogues as potential payloads in targeted therapeutics., Hemiasterlin, a highly cytotoxic marine natural product (see structure), was synthesised by a multicomponent approach with a longest linear sequence of 10 steps. Its use in a targeted therapeutic was demonstrated by incorporation as a payload in an antibody–drug conjugate (ADC), which showed mid‐picomolar cytotoxicity against HER2‐expressing cancer cell lines.

Prostate cancer is one of the leading causes of cancer-related death in men. The identification of new therapeutics to selectively target prostate cancer cells is therefore vital. Recently, the rotenoids rotenone (1) and deguelin (2) were reported to selectively kill prostate cancer cells and the inhibition of mitochondrial complex I was established as essential to their mechanism of action. However, these hydrophobic rotenoids readily cross the blood brain barrier and induce symptoms characteristic of Parkinson’s disease in animals. Since hydroxylated derivatives of 1 and 2 are more hydrophilic and less likely to readily cross the blood brain barrier, 29 natural and unnatural hydroxylated derivatives of 1 and 2 were synthesized for evaluation. The inhibitory potency (IC(50)) of each derivative against complex I was measured and its hydrophobicity (Slog(10)P) predicted. Amorphigenin (3), dalpanol (4), dihydroamorphigenin (5), and amorphigenol (6) were selected and evaluated in cell-based assays using C4-2 and C4-2B prostate cancer cells alongside control PNT2 prostate cells. These rotenoids inhibit complex I in cells, decrease oxygen consumption, and selectively inhibit the proliferation of prostate cancer cells, leaving control cells unaffected. The greatest selectivity and anti-proliferative effects were observed with 3 and 5. The data highlight these molecules as promising therapeutic candidates for further evaluation in prostate cancer models.

The aplyronines are a family of highly cytotoxic marine natural products with potential application in targeted cancer chemotherapy. To address the severe supply issue, function-oriented molecular editing of their macrolactone scaffold led to the design of a series of simplified aplyronine analogues. Enabled by a highly convergent aldol-based route, the total synthesis of four analogues was achieved, with a significant improvement in step economy versus previous compounds, and their cancer cell growth inhibition in the HeLa cell line was determined. The modular strategy presented offers a means for significantly shortening their chemical synthesis to facilitate the continued development of this promising class of anticancer agent.

Organic synthesis underpins the evolution of weak fragment hits into potent lead compounds. Deficiencies within current screening collections often result in the requirement of significant synthetic investment to enable multidirectional fragment growth, limiting the efficiency of the hit evolution process. Diversity-oriented synthesis (DOS)-derived fragment libraries are constructed in an efficient and modular fashion and thus are well-suited to address this challenge. To demonstrate the effective nature of such libraries within fragment-based drug discovery, we herein describe the screening of a 40-member DOS library against three functionally distinct biological targets using X-Ray crystallography. Firstly, we demonstrate the importance for diversity in aiding hit identification with four fragment binders resulting from these efforts. Moreover, we also exemplify the ability to readily access a library of analogues from cheap commercially available materials, which ultimately enabled the exploration of a minimum of four synthetic vectors from each molecule. In total, 10–14 analogues of each hit were rapidly accessed in three to six synthetic steps. Thus, we showcase how DOS-derived fragment libraries enable efficient hit derivatisation and can be utilised to remove the synthetic limitations encountered in early stage fragment-based drug discovery., Fragment-based screening of a shape-diverse collection yielded four hits against three proteins. Up to 14 analogues of each hit were rapidly generated, enabling four fragment growth vectors to be explored using inexpensive materials and reliable synthetic transformations.

Using N-sulfonyl triazoles as substrates, compounds as diverse as 2-imino tetrahydrofurans, 13- and 15-membered ring aza-macrocycles can be prepared selectively via formal [1 + 4], [5 + 4 + 4] and [3 + 4 + 4 + 4] condensations of α-imino carbenes and oxetanes under Rh(ii)-catalysis or thermal activation. Spirocyclic N-heterocycles are also accessible by means of Buchwald-Hartwig and Pictet-Spengler cyclizations. By reaction control, substrate selection or further derivatization, a large variety of chemical structures is thus achievable. Finally, using triazoles reacting under thermal activation, interesting mechanistic insight was obtained.

Macrocycles have long been recognized as useful chemical entities for medicine, with naturally occurring and synthetic macrocycles clinically approved for use as prescription drugs. Despite this promise, the synthesis of collections of macrocycles has been historically challenging due to difficulties in the formation of large rings. Diversity-Oriented Synthesis (DOS) emerged in the early 2000s as a powerful strategic solution to the construction of diverse molecular libraries. This review details the various strategies developed within the field of DOS for the synthesis of macrocycle libraries, utilizing modern synthetic methodology to deliver structurally diverse collections of macrocyclic molecules, and the exploration of their therapeutic potential. Section 1 of this work details the use of algorithmic strategies and is divided into Build/Couple/Pair, Advanced Build/Couple/Pair, Initiate/Propagate/Terminate, Fragment-Based Domain Shuffling, Two-Directional Synthesis, and Successive Ring Expansion. Section 2 covers strategies based on ring distortion reactions, including Sequential Cycloaddition/Fragmentation, Ring Expansions, and Miscellaneous.

Herein, we describe the development of a novel staple with an electrophilic warhead to enable the generation of stapled peptide covalent inhibitors of the p53-MDM2 protein-protein interaction (PPI). The peptide developed showed complete and selective covalent binding resulting in potent inhibition of p53-MDM2 PPI.

In recent years the pharmaceutical industry has benefited from the advances made in fragment-based drug discovery (FBDD) with more than 30 fragment-derived drugs currently marketed or progressing through clinical trials. The success of fragment-based drug discovery is entirely dependent upon the composition of the fragment screening libraries used. Heterocycles are prevalent within marketed drugs due to the role they play in providing binding interactions; consequently, heterocyclic fragments are important components of FBDD libraries. Current screening libraries are dominated by flat, sp2-rich compounds, primarily owing to their synthetic tractability, despite the superior physicochemical properties displayed by more three-dimensional scaffolds. Herein, we report step-efficient routes to a number of biologically relevant, fragment-like heterocyclic spirocycles. The use of both electron-deficient and electron-rich 2-atom donors was explored in complexity-generating [3+2]-cycloadditions to furnish products in 3 steps from commercially available starting materials. The resulting compounds were primed for further fragment elaboration through the inclusion of synthetic handles from the outset of the syntheses.

This work describes the efficient development of functionalised, cell-permeable, and stable peptide inhibitors of the protein–protein interaction of CK2., The discovery of new Protein–Protein Interaction (PPI) modulators is currently limited by the difficulties associated with the design and synthesis of selective small molecule inhibitors. Peptides are a potential solution for disrupting PPIs; however, they typically suffer from poor stability in vivo and limited tissue penetration hampering their wide spread use as new chemical biology tools and potential therapeutics. In this work, a combination of CuAAC chemistry, molecular modelling, X-ray crystallography, and biological validation allowed us to develop highly functionalised peptide PPI inhibitors of the protein CK2. The lead peptide, CAM7117, prevents the formation of the holoenzyme assembly in vitro, slows down proliferation, induces apoptosis in cancer cells and is stable in human serum. CAM7117 could aid the development of novel CK2 inhibitors acting at the interface and help to fully understand the intracellular pathways involving CK2. Importantly, the approach adopted herein could be applied to many PPI targets and has the potential to ease the study of PPIs by efficiently providing access to functionalised peptides.

Divinylpyrimidine (DVP) linkers enable access to highly stable and functional antibody–drug conjugates., Antibody–drug conjugates (ADCs) are a class of targeted therapeutics that utilize the specificity of antibodies to selectively deliver highly potent cytotoxins to target cells. Although recent years have witnessed significant interest in ADCs, problems remain with the standard linkage chemistries used for cytotoxin-antibody bioconjugation. These typically (1) generate unstable constructs, which may lead to premature cytotoxin release, (2) often give a wide variance in drug–antibody ratios (DAR) and (3) have poor control of attachment location on the antibody, resulting in a variable pharmacokinetic profile. Herein, we report a novel divinylpyrimidine (DVP) linker platform for selective bioconjugation via covalent re-bridging of reduced disulfide bonds on native antibodies. Model studies using the non-engineered trastuzumab antibody validate the utility of this linker platform for the generic generation of highly plasma-stable and functional antibody constructs that incorporate variable biologically relevant payloads (including cytotoxins) in an efficient and site-selective manner with precise control over DAR. DVP linkers were also used to efficiently re-bridge both monomeric and dimeric protein systems, demonstrating their potential utility for general protein modification, protein stabilisation or the development of other protein-conjugate therapeutics.

Protein–protein interactions (PPIs) are tremendously important for the function of many biological processes. However, because of the structure of many protein–protein interfaces (flat, featureless and relatively large), they have largely been overlooked as potential drug targets. In this review, we highlight the current tools used to study the molecular recognition of PPIs through the use of different peptidomimetics, from small molecules and scaffolds to peptides. Then, we focus on constrained peptides, and in particular, ways to constrain α-helices through stapling using both one- and two-component techniques.

The first total synthesis of bussealin E, a natural product with a unique cycloheptadibenzofuran scaffold, is reported. A strategy inspired by a proposed biosynthesis was employed whereby a diphenylpropane derivative underwent an oxidative phenolic coupling to forge the tetracyclic ring system. The synthesis of the diphenylpropane featured a key sp2–sp3 Hiyama coupling between a vinyldisiloxane and a benzylic bromide.