Copper is an essential cofactor for all organisms, and yet it becomes toxic if concentrations exceed a threshold maintained by evolutionarily conserved homeostatic mechanisms. How excess copper ...induces cell death, however, is unknown. Here, we show in human cells that copper-dependent, regulated cell death is distinct from known death mechanisms and is dependent on mitochondrial respiration. We show that copper-dependent death occurs by means of direct binding of copper to lipoylated components of the tricarboxylic acid (TCA) cycle. This results in lipoylated protein aggregation and subsequent iron-sulfur cluster protein loss, which leads to proteotoxic stress and ultimately cell death. These findings may explain the need for ancient copper homeostatic mechanisms.
We report the development of a multifunctional reagent for the direct conversion of pyridines to Boc-protected 2-aminopyridines with exquisite site selectivity and chemoselectivity. The novel reagent ...was prepared on 200-g scale in a single step, reacts in the title reaction under mild conditions without precautions toward air or moisture, and is tolerant of nearly all common functionality. Experimental and in situ spectroscopic monitoring techniques provide detailed insights and unexpected findings for the unique reaction mechanism.
α-Tertiary amines are a common motif in pharmaceutically important molecules but are challenging to prepare using asymmetric catalysis. Here, we demonstrate engineered flavin-dependent ...‘ene’-reductases (EREDs) can catalyze radical additions into oximes to prepare this motif. Two different EREDs were evolved into competent catalysts for this transformation with high levels of stereoselectivity. Mechanistic studies indicate that the oxime contributes to the enzyme templated charge-transfer complex formed between the substrate and cofactor. These products can be further derivatized to prepare a variety of motifs, highlighting the versatility of ERED photoenzymatic catalysis for organic synthesis.
Here, we report a novel “CyClick” strategy for the macrocyclization of peptides that works in an exclusively intramolecular fashion thereby precluding the formation of dimers and oligomers via ...intermolecular reactions. The CyClick chemistry is highly chemoselective for the N‐terminus of the peptide with a C‐terminal aldehyde. In this protocol, the peptide conformation internally directs activation of the backbone amide bond and thereby facilitates formation of a stable 4‐imidazolidinone‐fused cyclic peptide with high diastereoselectivity (>99 %). This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings with varying amino acid compositions in one pot under mild reaction conditions. The reaction generated peptide macrocycles featuring a 4‐imidazolidinone in their scaffolds, which acts as an endocyclic control element that promotes intramolecular hydrogen bonding and leads to macrocycles with conformationally rigid turn structures.
Exclusively intramolecular: The conformationally induced activation of the amide bond, the idea behind the “CyClick” strategy, is exploited for the macrocyclization of peptides and precludes the formation of dimers or oligomers via intermolecular reactions. This method is tolerant to a variety of peptide aldehydes and has been applied for the synthesis of 12‐ to 23‐membered rings.
Cyclic tetrapeptides exhibit high cellular permeability and a wide range of biological properties and thus have gained great interest in the field of medicinal chemistry. We synthesized highly ...strained 12-membered head to tail cyclic peptides with varying reactive amino acids, without oligomerization using the exclusively intramolecular CyClick chemistry. This occurs by a two-step process involving the low-energy formation of a 15 atom-containing cyclic imine, followed by a chemoselective ring contraction of the peptide backbone generating a highly strained 12 atom-containing cyclic tetrapeptide. This reaction exhibited high substrate scope and generated head to tail cyclic tetrapeptides with varying amino acids at the N-terminus, showing chemoselectivity without the need for side group protection.
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Pure shift NMR experiments greatly enhance spectral resolution by collapsing multiplet structures into singlets and, with water suppression, can be used for aqueous samples. Here, we combine ...ultra-clean pure-shift NMR (SAPPHIRE) with two different internally encoded water suppression schemes to achieve optimal performance for small molecule and macrocyclic peptide pharmaceuticals in water and acetonitrile-water mixtures.
Selective modification of proteins enables synthesis of antibody-drug conjugates, cellular drug delivery and construction of new materials. Many groups have developed methods for selective N-terminal ...modification without affecting the side chain of lysine by judicious pH control. This is due to lower basicity of the N-terminus relative to lysine side chains. But none of the methods are capable of selective modification of secondary amines or N-terminal proline, which has similar basicity as lysine. Here, we report a secondary amine selective Petasis (SASP) reaction for selective bioconjugation at N-terminal proline. We exploited the ability of secondary amines to form highly electrophilic iminium ions with aldehydes, which rapidly reacted with nucleophilic organoboronates, resulting in robust labeling of N-terminal proline under biocompatible conditions. This is the first time the Petasis reaction has been utilized for selective modification of secondary amines on completely unprotected peptides and proteins under physiological conditions. Peptide screening results showed that the reaction is highly selective for N-terminal proline. There are no other chemical methods reported in literature that are selective for N-terminal proline in both peptides and proteins. This is a multicomponent reaction leading to the synthesis of doubly functionalized bioconjugates in one step that can be difficult to achieve using other methods. The key advantage of the SASP reaction includes its high chemoselective and stereoselective (>99% de) nature, and it affords dual labeled proteins in one pot. The broad utility of this bioconjugation is highlighted for a variety of peptides and proteins, including aldolase and creatine kinase.
Secondary amine selective Petasis (SASP) bioconjugation for the selective labeling of peptides and proteins with N-terminal secondary amines.
Density functional theory (DFT) benchmark studies of 1H and 13C NMR chemical shifts often yield differing conclusions, likely due to non-optimal test molecules and non-standardized data acquisition. ...To address this issue, we carefully selected and measured 1H and 13C NMR chemical shifts for 50 structurally diverse small organic molecules containing atoms from only the first two rows of the periodic table. Our NMR dataset, DELTA50, was used to calculate linear scaling factors and to evaluate the accuracy of 73 density functionals, 40 basis sets, 3 solvent models, and 3 gauge-referencing schemes. The best performing DFT methodologies for 1H and 13C NMR chemical shift predictions were WP04/6-311++G(2d,p) and ωB97X-D/def2-SVP, respectively, when combined with the polarizable continuum solvent model (PCM) and gauge-independent atomic orbital (GIAO) method. Geometries should be optimized at the B3LYP-D3/6-311G(d,p) level including the PCM solvent model for the best accuracy. Predictions of 20 organic compounds and natural products from a separate probe set had root-mean-square deviations (RMSD) of 0.07 to 0.19 for 1H and 0.5 to 2.9 for 13C. Maximum deviations were less than 0.5 and 6.5 ppm for 1H and 13C, respectively.
An operationally simple oxidation–cyanation method for the synthesis of cyanamides is described. The procedure utilizes inexpensive and commercially available N-chlorosuccinimide and Zn(CN)2 as ...reagents to avoid direct handling of toxic cyanogen halides. It is demonstrated to be amenable for the cyanation of a variety of primary and secondary amines and aniline derivatives as well as a complex synthetic intermediate en route to verubecestat (MK-8931). Additionally, kinetic measurements and other control experiments are reported to shed light onto the mechanism of this cyanation reaction.
We report the development of a method for room-temperature C–H hydroxymethylation of heteroarenes. A key enabling advance in this work was achieved by implementing visible light photoredox catalysis ...that proved to be applicable to many classes of heteroarenes and tolerant of diverse functional groups found in druglike molecules.
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