Multitargeting compounds comprising activity on more than a single biological target have gained remarkable relevance in drug discovery owing to the complexity of multifactorial diseases such as cancer, inflammation, or the metabolic syndrome. Polypharmacological drug profiles can produce additive or synergistic effects while reducing side effects and significantly contribute to the high therapeutic success of indispensable drugs such as aspirin. While their identification has long been the result of serendipity, medicinal chemistry now tends to design polypharmacology. Modern in vitro pharmacological methods and chemical probes allow a systematic search for rational target combinations and recent innovations in computational technologies, crystallography, or fragment-based design equip multitarget compound development with valuable tools. In this Perspective, we analyze the relevance of multiple ligands in drug discovery and the versatile toolbox to design polypharmacology. We conclude that despite some ...

Polypharmacology by Design: A Medicinal Chemist’s Perspective on Multitargeting Compounds

The urea functionality is inherent to numerous bioactive compounds, including a variety of clinically approved therapies. Urea containing compounds are increasingly used in medicinal chemistry and drug design in order to establish key drug-target interactions and fine-tune crucial drug-like properties. In this perspective, we highlight physicochemical and conformational properties of urea derivatives. We provide outlines of traditional reagents and chemical procedures for the preparation of ureas. Also, we discuss newly developed methodologies mainly aimed at overcoming safety issues associated with traditional synthesis. Finally, we provide a broad overview of urea-based medicinally relevant compounds, ranging from approved drugs to recent medicinal chemistry developments.

Urea Derivatives in Modern Drug Discovery and Medicinal Chemistry

Salmeterol is a partial agonist for the β2 adrenergic receptor (β2AR) and the first long-acting β2AR agonist to be widely used clinically for the treatment of asthma and chronic obstructive pulmonary disease. Salmeterol's safety and mechanism of action have both been controversial. To understand its unusual pharmacological action and partial agonism, we obtained the crystal structure of salmeterol-bound β2AR in complex with an active-state-stabilizing nanobody. The structure reveals the location of the salmeterol exosite, where sequence differences between β1AR and β2AR explain the high receptor-subtype selectivity. A structural comparison with the β2AR bound to the full agonist epinephrine reveals differences in the hydrogen-bond network involving residues Ser2045.43 and Asn2936.55. Mutagenesis and biophysical studies suggested that these interactions lead to a distinct active-state conformation that is responsible for the partial efficacy of G-protein activation and the limited β-arrestin recruitment for salmeterol.

/pdf/structural-insights-into-binding-specificity-efficacy-and-500a40htnh.pdf

Structural insights into binding specificity, efficacy and bias of a beta2AR partial agonist.

Allosteric modulators bound to structurally diverse allosteric sites can achieve better pharmacological advantages than orthosteric ligands. The discovery of allosteric modulators, however, has been traditionally serendipitous, owing to the complex nature of allosteric modulation. Recent advances in the understanding of allosteric regulatory mechanisms and remarkable availability of structural data of allosteric proteins and modulators, as well as their complexes, have greatly contributed to the development of various computational approaches to guide the structure-based discovery of allosteric modulators. This Perspective first outlines the evolution of the allosteric concept and describes the advantages and hurdles facing allosteric modulator discovery. The current available computational approaches, together with experimental approaches aiming to highlight allosteric studies, are then highlighted, emphasizing successful examples with their combined applications. We aimed to increase the awareness of th...

Allosteric Modulator Discovery: From Serendipity to Structure-Based Design.

G-protein-coupled receptors (GPCRs) are the largest class of signaling receptors that are most frequently targeted by therapeutic drugs. Allosteric modulators bound to GPCRs at allosteric sites provide the potential for differential selectivity and improved safety compared with traditional orthosteric ligands. The recent breakthroughs in GPCR structural biology have made structures of GPCRs from classes A, B, C, and F complexed with small-molecule allosteric modulators available. Knowledge of the detailed receptor–modulator interactions at the allosteric sites is useful for structure-based GPCR drug design of novel therapeutics. This Perspective comprehensively summarizes the current status of structural complexes between GPCRs and their small-molecule allosteric modulators, particularly the key receptor–modulator interactions at the allosteric sites. Then, the structural diversity of allosteric sites across four GPCR subfamilies is compared. This study is expected to contribute to the design of GPCR allo...

Small Molecule Allosteric Modulators of G-Protein-Coupled Receptors: Drug-Target Interactions.

Herein, we report the development of bitopic ligands aimed at targeting the orthosteric binding site (OBS) and a metastable binding site (MBS) within the same receptor unit. Previous molecular dynamics studies on ligand binding to the β2-adrenergic receptor (β2AR) suggested that ligands pause at transient, less-conserved MBSs. We envisioned that MBSs can be regarded as allosteric binding sites and targeted by homobivalent bitopic ligands linking two identical pharmacophores. Such ligands were designed based on docking of the antagonist (S)-alprenolol into the OBS and an MBS and synthesized. Pharmacological characterization revealed ligands with similar potency and affinity, slightly increased β2/β1AR-selectivity, and/or substantially slower β2AR off-rates compared to (S)-alprenolol. Truncated bitopic ligands suggested the major contribution of the metastable pharmacophore to be a hydrophobic interaction with the β2AR, while the linkers alone decreased the potency of the orthosteric fragment. Altogether, the study underlines the potential of targeting MBSs for improving the pharmacological profiles of ligands.

Probing the Existence of a Metastable Binding Site at the β2-Adrenergic Receptor with Homobivalent Bitopic Ligands

We previously reported potent ligands and inhibitors of Mycobacterium tuberculosis dethiobiotin synthetase (MtDTBS), a promising target for antituberculosis drug development (Schumann et al., ACS Chem Biol. 2021, 16, 2339-2347); here the unconventional origin of the fragment compound they were derived from is described for the first time. Compound 1 (9b-hydroxy-6b,7,8,9,9a,9b-hexahydrocyclopenta[3,4]cyclobuta[1,2-c]chromen-6(6aH)-one), identified by in silico fragment screen, was subsequently shown by surface plasmon resonance to have dose-responsive binding (KD 0.6 mM). Clear electron density was revealed in the DAPA substrate binding pocket, when 1 was soaked into MtDTBS crystals, but the density was inconsistent with the structure of 1. Here we show the lactone of 1 hydrolyses to carboxylic acid 2 under basic conditions, including those of the crystallography soak, with subsequent ring-opening of the component cyclobutane ring to form cyclopentylacetic acid 3. Crystals soaked directly with authentic 3 produced electron density that matched that of crystals soaked with presumed 1, confirming the identity of the bound ligand. The synthetic utility of fortuitously formed 3 enabled subsequent compound development into nanomolar inhibitors. Our findings represent an example of chemical modification within drug discovery assays and demonstrate the value of high-resolution structural data in the fragment hit validation process. Synopsis A molecule flagged in an in silico docking screen against MtDTBS, was inadvertently hydrolysed in the crystal conditions used for hit validation. The resulting fragment-sized molecule bound to the DAPA substrate binding pocket of the target enzyme (MtDTBS) with millimolar affinity, as measured by surface plasmon resonance, but was later modified to a highly potent (nanomolar) ligand and promising lead for the development of novel tuberculosis treatments. Graphical Abstract

/pdf/fortuitous-in-vitro-compound-degradation-produces-a-13720taq.pdf

Fortuitous in vitro compound degradation produces a tractable hit against Mycobacterium tuberculosis dethiobiotin synthetase: a cautionary tale of what goes in, does not always come out

G protein-coupled receptors (GPCRs) belong to a large superfamily of membrane receptors mediating a variety of physiological functions. As such they are attractive targets for drug therapy. However, it remains a challenge to develop subtype selective GPCR ligands due to the high conservation of orthosteric binding sites. Bitopic ligands have been employed to address the selectivity problem by combining (linking) an orthosteric ligand with an allosteric modulator, theoretically leading to high-affinity subtype selective ligands. However, it remains a challenge to identify suitable allosteric binding sites. Computational studies on ligand binding to GPCRs have revealed transient, low-affinity binding sites, termed metastable binding sites. Metastable binding sites may provide a new source of allosteric binding sites that could be exploited in the design of bitopic ligands. Unlike the bitopic ligands that have been reported to date, this type of bitopic ligands would be composed of two identical pharmacophor...

Bitopic Ligands and Metastable Binding Sites: Opportunities for G Protein-Coupled Receptor (GPCR) Medicinal Chemistry.

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Probing the Existence of a Metastable Binding Site at the β2-Adrenergic Receptor with Homobivalent Bitopic Ligands

Fortuitous in vitro compound degradation produces a tractable hit against Mycobacterium tuberculosis dethiobiotin synthetase: a cautionary tale of what goes in, does not always come out

Bitopic Ligands and Metastable Binding Sites: Opportunities for G Protein-Coupled Receptor (GPCR) Medicinal Chemistry.