Comprehensive Strategies to Bicyclic Prolines: Applications in the Synthesis of Potent Arginase Inhibitors

A Photochemical Strategy for the Conversion of Nitroarenes into Rigidified Pyrrolidine Analogues

Bicyclic amines are important motifs for the preparation of bioactive materials. These species have well-defined exit vectors that enable accurate disposition of substituents toward specific areas of chemical space. Of all possible skeletons, the 2-azabicyclo[3.2.0]heptane framework is virtually absent from MedChem libraries due to a paucity of synthetic methods for its preparation. Here, we report a modular synthetic strategy that utilizes nitroarenes as flat and easy-to-functionalize feedstocks for the assembly of these sp3-rich materials. Mechanistically, this approach exploits two concomitant photochemical processes that sequentially ring-expand the nitroarene into an azepine and then fold it into a rigid bicycle pyrroline by means of singlet nitrene-mediated nitrogen insertion and excited-state-4π electrocyclization. A following hydrogenolysis provides, with full diastereocontrol, the desired bicyclic amine derivatives whereby the aromatic substitution pattern has been translated into the one of the three-dimensional heterocycle. These molecules can be considered rigid pyrrolidine analogues with a well-defined orientation of their substituents. Furthermore, unsupervised clustering of an expansive virtual database of saturated N-heterocycles revealed these derivatives as effective isosteres of rigidified piperidines. Overall, this platform enables the conversion of nitroarene feedstocks into complex sp3-rich heterocycles of potential interest to drug development.

Synthesis of 2-Azanorbornanes via Strain-Release Formal Cycloadditions Initiated by Energy Transfer

Rigid bicycles are becoming more popular in the pharmaceutical industry because they allow for expansion to new and unique chemical spaces. This work describes a new strategy to construct 2-azanorbornanes, which can act as rigid piperidine/pyrrolidine scaffolds with well-defined exit vectors. To achieve the synthesis of 2-azanorbornanes, new strain-release reagent, azahousane, is introduced along with its photosensitized strain-release formal cycloaddition with alkenes. Furthermore, new reactivity between a housane and an imine is disclosed. Both strategies lead to various substituted 2-azanorbornanes with good selectivities.

Discovery of non-boronic acid Arginase 1 inhibitors through virtual screening and biophysical methods

Inhibiting Arginase 1 (ARG1), a metalloenzyme that hydrolyzes l-arginine in the urea cycle, has been demonstrated as a promising therapeutic avenue in immuno-oncology through the restoration of suppressed immune response in several types of cancers. Most of the currently reported small molecule inhibitors are boronic acid based. Herein, we report the discovery of non-boronic acid ARG1 inhibitors through virtual screening. Biophysical and biochemical methods were used to experimentally profile the hits while X-ray crystallography confirmed a class of trisubstituted pyrrolidine derivatives as optimizable alternatives for the development of novel classes of immuno-oncology agents targeting this enzyme.

Insight into Stereocontrol in the Asymmetric Intramolecular Allylation with a tert-Butylsulfinamide Nucleophile: Application in the Synthesis of Chiral Isoindoline-1-Carboxylic Acid Esters

The asymmetric induction afforded by a chiral sulfinyl group in a palladium/Brønsted-acid-catalyzed intramolecular allylic amination was investigated. Predictions of the diastereoselectivity for various substrates under assumed total thermodynamic control were obtained from density functional theory (DFT), and the correlation with experimental data demonstrates abrupt changes to kinetic control across the substrate scope. The resulting heterocyclic product was readily converted to valuable isoindoline-1-carboxylic acid esters by a two-step oxidation sequence, providing asymmetric access to a key unnatural α-amino acid scaffold.

Pseudoprolines as stereoelectronically tunable proline isosteres

The cyclic structure of proline (Pro) confers unique conformational properties on this natural amino acid that influences polypeptide structure and function. Pseudoprolines are a family of Pro isosteres that incorporate a heteroatom, most prominently oxygen or sulfur but also silicon and selenium, to replace the C_β or C_γ carbon atom of the pyrrolidine ring. These readily synthetically accessible structural motifs can facilitate facile molecular editing in a fashion that allows modulation of the amide bond topology of dipeptide elements and influence over ring pucker. While the properties of pseudoprolines have been exploited most prominently in the design of oligopeptide analogues, they have potential application in the design and optimization of small molecules. In this Digest, we summarize the physicochemical properties of pseudoprolines and illustrate their potential in drug discovery by surveying examples of applications in the design of bioactive molecules.

Virus-Induced Membrane Fusion in Neurodegenerative Disorders

A growing body of epidemiological and research data has associated neurotropic viruses with accelerated brain aging and increased risk of neurodegenerative disorders. Many viruses replicate optimally in senescent cells, as they offer a hospitable microenvironment with persistently elevated cytosolic calcium, abundant intracellular iron, and low interferon type I. As cell-cell fusion is a major driver of cellular senescence, many viruses have developed the ability to promote this phenotype by forming syncytia. Cell-cell fusion is associated with immunosuppression mediated by phosphatidylserine externalization that enable viruses to evade host defenses. In hosts, virus-induced immune dysfunction and premature cellular senescence may predispose to neurodegenerative disorders. This concept is supported by novel studies that found postinfectious cognitive dysfunction in several viral illnesses, including human immunodeficiency virus-1, herpes simplex virus-1, and SARS-CoV-2. Virus-induced pathological syncytia may provide a unified framework for conceptualizing neuronal cell cycle reentry, aneuploidy, somatic mosaicism, viral spreading of pathological Tau and elimination of viable synapses and neurons by neurotoxic astrocytes and microglia. In this narrative review, we take a closer look at cell-cell fusion and vesicular merger in the pathogenesis of neurodegenerative disorders. We present a "decentralized" information processing model that conceptualizes neurodegeneration as a systemic illness, triggered by cytoskeletal pathology. We also discuss strategies for reversing cell-cell fusion, including, TMEM16F inhibitors, calcium channel blockers, senolytics, and tubulin stabilizing agents. Finally, going beyond neurodegeneration, we examine the potential benefit of harnessing fusion as a therapeutic strategy in regenerative medicine.