Jeffrey N&Period; Johnston1<&Sol;A<&Sol;Span<&Sol;Sup&Period

Background: Abnormal sarcoplasmic reticulum (SR) Ca ²⁺ release through ryanodine receptor 2 (RyR2) is a well-established mechanism of ventricular arrhythmias. Whether persistent RyR2 dysfunction can also initiate the structural remodeling characteristic of arrhythmogenic cardiomyopathy (ACM) remains unknown. We tested the hypothesis that chronic RyR2-mediated Ca ²⁺ leak is sufficient to couple electrical instability to progressive cardiomyopathy. Methods: We generated a rabbit carrying the severe gain-of-function RyR2-V2475F mutation and characterized disease progression using longitudinal cardiac phenotyping, continuous electrocardiographic monitoring, cellular electrophysiology and Ca ²⁺ imaging, histopathology, biochemical analyses, and single-nucleus RNA sequencing (snRNA-seq). Therapeutic potential was evaluated by continuous treatment with the selective RyR2 inhibitor ent -verticilide for two months. Results: RyR2-V2475F rabbits developed spontaneous ventricular tachyarrhythmias, sudden cardiac death, and progressive right ventricular (RV)-dominant fibrofatty cardiomyopathy recapitulating major features of human ACM. Malignant ventricular arrhythmias preceded overt structural remodeling and were associated at the cellular level with early spontaneous Ca ²⁺ release and early afterdepolarizations. Early disease was characterized by remodeling of excitation-contraction coupling with preserved SR Ca ²⁺ load and contractile function despite RyR2 dysfunction; upon disease progression, these compensatory changes were accompanied by SR Ca ²⁺ depletion, impaired RV contractility and reduced left ventricular filling. Single-nucleus transcriptomics identified early fibroblast expansion and predicted cardiomyocyte-centered paracrine signaling before advanced fibrofatty infiltration. Cardiomyocytes also exhibited an altered lipid-metabolic transcriptome and intracellular lipid accumulation, accompanied by enhanced mitochondrial Ca ²⁺ uptake. Selective RyR2 inhibition markedly reduced ventricular tachycardia burden and preserved RV contraction and LV filling during disease progression. Conclusions: Severe RyR2 gain-of-function can lead to both malignant ventricular arrhythmias and progressive arrhythmogenic cardiomyopathy in a large-animal model, establishing persistent intracellular Ca ²⁺ dysregulation as a mechanistic link between electrical and structural heart disease. The ability of selective RyR2 inhibition to suppress arrhythmias and preserve cardiac function identifies RyR2 as a potentially actionable therapeutic target in arrhythmogenic cardiomyopathy.

Nitrones are reactive dipoles for cycloadditions that have been used for powerful alkene difunctionalization reactions, often stereocontrolled. Despite the wealth of knowledge generated over a half-century of study, reports of N-acyl nitrones are exceedingly rare, with limited options for their access. We report a new diverted Umpolung Amide Synthesis (UmAS) reaction that leads to N-acyl nitrones through an intermolecular carbon–nitrogen bond formation. These nitrones are rare examples of doubly acylated species (C- and N-acyl) that are expected to engage electron-rich alkenes in Type III dipolar cycloadditions. Our findings suggest, unexpectedly, that these species are more fleeting than previously reported, succumbing to a rapid N→O acyl transfer reaction that leads to stable O-acyl oximes.

Ryanodine receptor 2 (RyR2) hyperactivity is frequently observed in structural heart disease (SHD), commonly caused by ischemic heart disease. This aberrant Ca ²⁺ release promotes irregular electrical activity and life‐threatening arrhythmias. Our previous work demonstrated that the pan‐ryanodine receptor (RyR) inhibitor dantrolene can reverse arrhythmogenic substrates, but its lack of RyR2 selectivity limits its therapeutic potential. The unnatural verticilide enantiomer ( ent ‐verticilide) was identified as a selective RyR2 inhibitor, showing promising specificity without activating skeletal muscle RyR1. This study evaluated the antiarrhythmic potential of a selective RyR2 antagonist, ent ‐(+)‐verticilide ( ent ‐Vert), in human ventricular slices. Right and left ventricular slices were prepared from human hearts not designated for transplantation. Pseudo‐electrocardiograms (ECG) tracked premature ventricular contraction (PVC) incidence, and optical mapping identified arrhythmogenic substrates. Baseline optical recordings were obtained before treatment with isoproterenol (Iso) (250 nM) and caffeine (200 µM) to induce Ca ^{2 +} leak and arrhythmogenic activity, followed by sequential ent ‐Vert application (1 and 3 µM). The effects of ent ‐Vert alone were tested with baseline recordings followed by a single 3 µM dose. Iso and caffeine increased PVC incidence in both right (RV) and left ventricular (LV) slices, but ent ‐Vert (1 and 3 µM) significantly reduced it. Iso and caffeine also shortened action potential duration (APD) in both slice types, but ent ‐Vert, after Iso and caffeine or alone (under control conditions), did not significantly change APD. In conclusion, ent ‐Vert suppressed arrhythmic triggers and reduced arrhythmogenic substrates in human ventricular slices, highlighting its potential as a targeted antiarrhythmic therapy for SHD. image Key points: RyR2 hyperactivity is a major driver of arrhythmias in structural heart disease, producing abnormal Ca ^{2 +} release and premature ventricular contractions. The RyR2‐selective inhibitor ent ‐Vert was evaluated in human RV and LV slices to determine its antiarrhythmic potential. β‐Adrenergic and RyR2 activation with Iso + caffeine induced Ca ^{2 +} leak, ectopic beats and shortened APD. Sequential ent ‐Vert application (1 and 3 µM) significantly suppressed ectopy incidence in a dose‐dependent manner. ent ‐Vert did not alter APD or conduction velocity under control or stimulated conditions, demonstrating that it suppresses arrhythmic triggers without disrupting normal cardiac electrophysiology.

A total synthesis of the macrocyclic depsipeptides cochinmicin I and V leveraged Umpolung Amide Synthesis (UmAS) alongside conventional amide and ester synthesis.

The preparation of peptidic molecules is a mainstay of synthesis, creating new tools that advance chemical biology, catalysis, and drug discovery. Despite the wide adoption of methods for amide synthesis based on electrophilic acyl transfer reactions, significant limitations remain that restrict access to chemical space and plague accessible peptides with imperfect conservation of stereochemical information. These problems persist in key applications (i.e., solid phase peptide synthesis) where reagent excess can be used to drive maximal yield. As a general tactic, however, use of excess coupling agents that are often hazardous is unsustainable. Here we report the synthesis of the antiviral tridecapeptide feglymycin where half of the amides are formed using umpolung amide synthesis (UmAS) to replace conventional amide synthesis. Reliance on UmAS further allowed the enantioselective synthesis of each noncanonical residue from an inexpensive aldehyde. As a result, the most process‐intensive components were simplified to a chiral Brønsted acid organocatalyst and potassium iodide/urea·hydrogen peroxide (KI/UHP). This solution‐phase total synthesis illustrates the harmonious, strategic application of complementary amide synthesis methods, and it serves as a touchstone for the green synthesis of peptides composed of noncanonical amino amides.

The preparation of peptidic molecules is a mainstay of synthesis, creating new tools that advance chemical biology, catalysis, and drug discovery. Despite the wide adoption of methods for amide synthesis based on electrophilic acyl transfer reactions, significant limitations remain that restrict access to chemical space and plague accessible peptides with imperfect conservation of stereochemical information. These problems persist in key applications (i.e., solid phase peptide synthesis) where reagent excess can be used to drive maximal yield. As a general tactic, however, use of excess coupling agents that are often hazardous is unsustainable. Here we report the synthesis of the antiviral tridecapeptide feglymycin where half of the amides are formed using umpolung amide synthesis (UmAS) to replace conventional amide synthesis. Reliance on UmAS further allowed the enantioselective synthesis of each noncanonical residue from an inexpensive aldehyde. As a result, the most process‐intensive components were simplified to a chiral Brønsted acid organocatalyst and potassium iodide/urea·hydrogen peroxide (KI/UHP). This solution‐phase total synthesis illustrates the harmonious, strategic application of complementary amide synthesis methods, and it serves as a touchstone for the green synthesis of peptides composed of noncanonical amino amides.

The development of highly enantioselective reactions often requires the adventitious discovery of a promising chiral catalyst and its resource-intensive optimization to high selectivity and generality. We report an approach less dependent on happenstance, whereby the performance of a single chiral ligand is enhanced not by modification of the architecturally complex chiral features but instead by an achiral counteranion. Critical to this strategy and its general application is the tactical development of N-aryl trifluoromethyl sulfonamide Brønsted acid donors and their ability to unlock the full enantioselectivity potential of a single chiral Brønsted basic ligand for the enantioselective addition of azide to nitroalkene.