Chirality: a key parameter in chemical probes.

Many small molecule bioactive and marketed drugs are chiral. They are often synthesised from commercially available chiral building blocks. However, chirality is sometimes incorrectly assigned by manufacturers with consequences for the end user ranging from: experimental irreproducibility, wasted time on synthesising the wrong product and reanalysis, to the added cost of purchasing the precursor and resynthesis of the correct stereoisomer. Further on, this could lead to loss of reputation, loss of funding, to safety and ethical concerns due to potential in vivo administration of the wrong form of a drug. It is our firm belief that more stringent control of chirality be provided by the supplier and, if needed, requested by the end user, to minimise the potential issues mentioned above. Certification of chirality would bring much needed confidence in chemical structure assignment and could be provided by a variety of techniques, from polarimetry, chiral HPLC, using known chiral standards, vibrational circular dichroism, and x-ray crystallography. A few case studies of our brushes with wrong chirality assignment are shown as well as some examples of what we believe to be good practice.

Efficient, multi-hundred-gram scale access to E3 ubiquitin ligase ligands for degrader development.

Small molecule heterobifunctional degraders (commonly also known as PROTACs) offer tremendous potential to deliver new therapeutics in areas of unmet medical need. To deliver on this promise, a new discipline directed at degrader design and optimization has emerged within medicinal chemistry to address a central challenge, namely how to optimize relatively large, heterobifunctional molecules for activity, whilst maintaining drug-like properties. This process involves simultaneous optimization of the three principle degrader components: E3 ubiquitin ligase ligand, linker, and protein of interest (POI) ligand. A substantial degree of commonality exists with the E3 ligase ligands typically used at the early stages of degrader development, resulting in demand for these compounds as chemical building blocks in degrader research programs. We describe herein a collation of large scale, high-yielding syntheses to access the most utilized E3 ligase ligands to support early-stage degrader development.

Developing, Choosing, and Using the Chemical Toolbox for Infectious Diseases Research.

Scientific progress is built on "what went before". As research in a field or discipline progresses, laying strong and scientifically correct foundations for each incremental discovery ultimately accelerates progress. The importance of "research tools" (e.g., chemical probes, antibodies, assays) that underpin researchers' efforts to probe and understand biological systems and pathways should therefore not be underestimated. Appropriate validation, protocol development, and ultimately availability of research tools are critical, in parallel with education on the appropriate selection and use of these tools.

Diastereomeric Resolution Yields Highly Potent Inhibitor of SARS-CoV-2 Main Protease.

SARS-CoV-2 is the causative agent behind the COVID-19 pandemic. The main protease (Mpro, 3CLpro) of SARS-CoV-2 is a key enzyme that processes polyproteins translated from the viral RNA. Mpro is therefore an attractive target for the design of inhibitors that block viral replication. We report the diastereomeric resolution of the previously designed SARS-CoV-2 Mpro α-ketoamide inhibitor 13b. The pure (S,S,S)-diastereomer, 13b-K, displays an IC50 of 120 nM against the Mpro and EC50 values of 0.8-3.4 µM for antiviral activity in different cell types. Crystal structures have been elucidated for the Mpro complexes with each of the major diastereomers, the active (S,S,S)-13b (13b-K), and the nearly inactive (R,S,S)-13b (13b-H); results for the latter reveal a novel binding mode. Pharmacokinetic studies show good levels of 13b-K after inhalative as well as after peroral administration. The active inhibitor (13b-K) is a promising candidate for further development as an antiviral treatment for COVID-19.

Scale-up and optimization of the synthesis of dual CBP/BRD4 inhibitor ISOX-DUAL.

ISOX-DUAL is a dual inhibitor of CBP/p300 (IC50 = 0.65 µM) and BRD4 (IC50 = 1.5 µM) bromodomains, and a useful chemical probe for epigenetic research. Aspects of the published synthetic route to this compound and its analogues are small-scale, poor-yielding or simply unamenable to scale-up without optimization. Herein we describe the development of a refined synthesis that circumvents the challenges of the original report, with notable improvements to several of the key synthetic transformations. Moreover, a general Suzuki Miyaura protocol for the late stage installation of alternative dimethyl-isoxazole acetyl-lysine (KAc) binding motifs is presented.

Inactivation of the CIC-DUX4 oncogene through P300/CBP inhibition, a therapeutic approach for CIC-DUX4 sarcoma.

CIC-DUX4 sarcoma (CDS) is a highly aggressive and metastatic small round type of predominantly pediatric sarcoma driven by a fusion oncoprotein comprising the transcriptional repressor Capicua (CIC) fused to the C-terminal transcriptional activation domain of DUX4. CDS rapidly develops resistance to chemotherapy, thus novel specific therapies are greatly needed. We demonstrate that CIC-DUX4 requires P300/CBP to induce histone H3 acetylation, activate its targets, and drive oncogenesis. We describe the synthetic route to a selective and highly potent P300/CBP inhibitor named iP300w and related stereoisomers, and find that iP300w efficiently suppresses CIC-DUX4 transcriptional activity and reverses CIC-DUX4 induced acetylation. iP300w is active at 100-fold lower concentrations than related stereoisomers or A-485. At low doses, iP300w shows specificity to CDS cancer cell lines, rapidly inducing cell cycle arrest and preventing growth of established CDS xenograft tumors when delivered in vivo. The effectiveness of iP300w to inactivate CIC-DUX4 highlights a promising therapeutic opportunity for CDS.

Reviewing the toolbox for degrader development in oncology.

The field of targeted protein degradation encompasses a growing number of modalities that achieve potent and selective knockdown of target proteins at the post-translational level. Among the most clinically advanced are bifunctional small-molecule degraders, also referred to as PROteolysis Targeting Chimeras, Degronimids, SNIPERs, or uSMITEs. Although applicable to many disease indications, oncology stands to be the first to benefit from this promising therapeutic approach, with the first investigational new drugs (INDs) filed in 2019 and a proliferation of research specifically focused on harnessing degraders for cancer treatment. In this review, we consider the toolbox of guidelines, reagents, and technologies that has evolved alongside the field to support degrader research and development.

Solution Structure and Conformational Dynamics of a Doublet Acyl Carrier Protein from Prodigiosin Biosynthesis.

The acyl carrier protein (ACP) is an indispensable component of both fatty acid and polyketide synthases and is primarily responsible for delivering acyl intermediates to enzymatic partners. At present, increasing numbers of multidomain ACPs have been discovered with roles in molecular recognition of trans-acting enzymatic partners as well as increasing metabolic flux. Further structural information is required to provide insight into their function, yet to date, the only high-resolution structure of this class to be determined is that of the doublet ACP (two continuous ACP domains) from mupirocin synthase. Here we report the solution nuclear magnetic resonance (NMR) structure of the doublet ACP domains from PigH (PigH ACP1-ACP2), which is an enzyme that catalyzes the formation of the bipyrrolic intermediate of prodigiosin, a potent anticancer compound with a variety of biological activities. The PigH ACP1-ACP2 structure shows each ACP domain consists of three conserved helices connected by a linker that is partially restricted by interactions with the ACP1 domain. Analysis of the holo (4'-phosphopantetheine, 4'-PP) form of PigH ACP1-ACP2 by NMR revealed conformational exchange found predominantly in the ACP2 domain reflecting the inherent plasticity of this ACP. Furthermore, ensemble models obtained from SAXS data reveal two distinct conformers, bent and extended, of both apo (unmodified) and holo PigH ACP1-ACP2 mediated by the central linker. The bent conformer appears to be a result of linker-ACP1 interactions detected by NMR and might be important for intradomain communication during the biosynthesis. These results provide new insights into the behavior of the interdomain linker of multiple ACP domains that may modulate protein-protein interactions. This is likely to become an increasingly important consideration for metabolic engineering in prodigiosin and other related biosynthetic pathways.

Developing degraders: principles and perspectives on design and chemical space.

Degraders (e.g. PROTACs, SNIPERs, degronimers etc.) are a new modality offering increasing potential both as tools for basic research and therapeutic development. They occupy chemical space that lies outside the classical Lipinski 'Rule of 5', which poses fresh challenges for achieving cell permeability and oral bioavailability. This study presents a comprehensive database of degrader structures from the peer reviewed literature, including both optimized degraders and first generation compounds, in order to provide a thorough assessment of the chemical space associated with this modality and identify common trends used during the 'hit to lead' process. The results provide insights into this new area of chemical space as well as pointers for degrader design, which we anticipate will be useful for researchers entering this field.

The Effect of Pre-Analytical Conditions on Blood Metabolomics in Epidemiological Studies.

Serum and plasma are commonly used in metabolomic-epidemiology studies. Their metabolome is susceptible to differences in pre-analytical conditions and the impact of this is unclear. Participant-matched EDTA-plasma and serum samples were collected from 37 non-fasting volunteers and profiled using a targeted nuclear magnetic resonance (NMR) metabolomics platform (n = 151 traits). Correlations and differences in mean of metabolite concentrations were compared between reference (pre-storage: 4 °C, 1.5 h; post-storage: no buffer addition delay or NMR analysis delay) and four pre-storage blood processing conditions, where samples were incubated at (i) 4 °C, 24 h; (ii) 4 °C, 48 h; (iii) 21 °C, 24 h; and (iv) 21 °C, 48 h, before centrifugation; and two post-storage sample processing conditions in which samples thawed overnight (i) then left for 24 h before addition of sodium buffer followed by immediate NMR analysis; and (ii) addition of sodium buffer, then left for 24 h before NMR profiling. We used multilevel linear regression models and Spearman's rank correlation coefficients to analyse the data. Most metabolic traits had high rank correlation and minimal differences in mean concentrations between samples subjected to reference and the different conditions tested, that may commonly occur in studies. However, glycolysis metabolites, histidine, acetate and diacylglycerol concentrations may be compromised and this could bias results in association/causal analyses.

Application of the Exactive Plus EMR for automated protein-ligand screening by non-covalent mass spectrometry.

RATIONALE: Non-covalent mass spectrometry (MS) offers considerable potential for protein-ligand screening in drug discovery programmes. However, there are some limitations with the time-of-flight (TOF) instrumentation typically employed that restrict the application of non-covalent MS in industrial laboratories. METHODS: An Exactive Plus EMR mass spectrometer was investigated for its ability to characterise non-covalent protein-small molecule interactions. Nano-electrospray ionisation (nanoESI) infusion was achieved with a TriVersa NanoMate. The transport multipole and ion lens voltages, dissociation energies and pressure in the Orbitrap™ were optimised. Native MS was performed, with ligand titrations to judge retention of protein-ligand interactions, serial dilutions of native proteins as an indication of sensitivity, and a heterogeneous protein analysed for spectral resolution. RESULTS: Interactions between native proteins and ligands are preserved during analysis on the Exactive Plus EMR, with the binding affinities determined in good agreement with expected values. High spectral resolution allows baseline separation of adduct ions, which should improve the accuracy and limit of detection for measuring ligand interactions. Data are also presented showing baseline resolution of glycoforms of a highly glycosylated protein, allowing binding of a fragment molecule to be detected. CONCLUSIONS: The high sensitivity and spectral resolution achievable with the Orbitrap technology confer significant advantages over TOF mass spectrometers, and offer a solution to current limitations regarding throughput, data analysis and sample requirements. A further benefit of improved spectral resolution is the possibility of using heterogeneous protein samples such as glycoproteins for fragment screening. This would significantly expand the scope of applicability of non-covalent MS in the pharmaceutical and other industries.

Identification of differential protein binding affinities in an atropisomeric pharmaceutical compound by noncovalent mass spectrometry, equilibrium dialysis, and nuclear magnetic resonance.

Atropisomerism of pharmaceutical compounds is a challenging area for drug discovery programs (Angew. Chem., Int. Ed. 2009, 48, 6398-6401). Strategies for dealing with these compounds include raising the energy barrier to atropisomerization in order to develop the drug as a single isomer (Tetrahedron 2004, 60, 4337-4347) or reducing the barrier to rotation and developing a mixture of rapidly interconverting isomers (Chirality 1996, 8, 364-371). Commonly, however, the atropisomers will be differentiated in terms of their affinity for a given protein target, and it is therefore important to rapidly identify the most active component prior to further compound development. We present equilibrium dialysis and saturation transfer difference NMR (STD-NMR) as techniques for assessing relative affinities of an atropisomeric mixture against antiapoptotic protein targets Bcl-2 and Bcl-xL. These techniques require no prior separation of the mixture of compounds and are therefore rapid and simple approaches. We also explore the use of noncovalent mass spectrometry for determining KD values of individual atropisomers separated from the equilibrium mixture and compare the results to solution-phase measurements. Results from equilibrium dialysis, STD-NMR, and noncovalent mass spectrometry are all in excellent agreement and provide complementary information on differential binding, amplification of the strongest binders, and KD values.

Automated protein-ligand interaction screening by mass spectrometry.

Identifying protein-ligand binding interactions is a key step during early-stage drug discovery. Existing screening techniques are often associated with drawbacks such as low throughput, high sample consumption, and dynamic range limitations. The increasing use of fragment-based drug discovery (FBDD) demands that these techniques also detect very weak interactions (mM K(D) values). This paper presents the development and validation of a fully automated screen by mass spectrometry, capable of detecting fragment binding into the millimolar K(D) range. Low sample consumption, high throughput, and wide dynamic range make this a highly attractive, orthogonal approach. The method was applied to screen 157 compounds in 6 h against the anti-apoptotic protein target Bcl-x(L). Mass spectrometry results were validated using STD-NMR, HSQC-NMR, and ITC experiments. Agreement between techniques suggests that mass spectrometry offers a powerful, complementary approach for screening.

Analysis of Streptomyces coelicolor phosphopantetheinyl transferase, AcpS, reveals the basis for relaxed substrate specificity.

The transfer of the phosphopantetheine chain from coenzyme A (CoA) to the acyl carrier protein (ACP), a key protein in both fatty acid and polyketide synthesis, is catalyzed by ACP synthase (AcpS). Streptomyces coelicolor AcpS is a doubly promiscuous enzyme capable of activation of ACPs from both fatty acid and polyketide synthesis and catalyzes the transfer of modified CoA substrates. Five crystal structures have been determined, including those of ligand-free AcpS, complexes with CoA and acetyl-CoA, and two of the active site mutants, His110Ala and Asp111Ala. All five structures are trimeric and provide further insight into the mechanism of catalysis, revealing the first detailed structure of a group I active site with the essential magnesium in place. Modeling of ACP binding supported by mutational analysis suggests an explanation for the promiscuity in terms of both ACP partner and modified CoA substrates.