Selective covalent targeting of GPX4 using masked nitrile-oxide electrophiles.

We recently described glutathione peroxidase 4 (GPX4) as a promising target for killing therapy-resistant cancer cells via ferroptosis. The onset of therapy resistance by multiple types of treatment results in a stable cell state marked by high levels of polyunsaturated lipids and an acquired dependency on GPX4. Unfortunately, all existing inhibitors of GPX4 act covalently via a reactive alkyl chloride moiety that confers poor selectivity and pharmacokinetic properties. Here, we report our discovery that masked nitrile-oxide electrophiles, which have not been explored previously as covalent cellular probes, undergo remarkable chemical transformations in cells and provide an effective strategy for selective targeting of GPX4. The new GPX4-inhibiting compounds we describe exhibit unexpected proteome-wide selectivity and, in some instances, vastly improved physiochemical and pharmacokinetic properties compared to existing chloroacetamide-based GPX4 inhibitors. These features make them superior tool compounds for biological interrogation of ferroptosis and constitute starting points for development of improved inhibitors of GPX4.

Divergent Total Syntheses of Rhodomyrtosones A and B.

Herein, we report total syntheses of the tetramethyldihydroxanthene natural product rhodomyrtosone B and the related bis-furan ß-triketone natural product rhodomyrtosone A. Nickel-(II)-catalyzed 1,4-conjugate addition of an α-alkylidene-ß-dicarbonyl substrate was developed to access the congener rhodomyrtosone B, and oxygenation of the same monoalkylidene derivative followed by cyclization was employed to obtain the bis-furan natural product rhodomyrtosone A.

Enantioselective total synthesis of (-)-maoecrystal V.

The enantioselective synthesis of maoecrystal V, a cytotoxic polycyclic diterpene, is described. Key reactions in the synthesis include an intramolecular Heck reaction, an oxidative cycloetherification, and an intermolecular Diels-Alder reaction to forge the carbocyclic core in a concise and stereoselective manner. Late-stage amine and C-H oxidation is used to install the final functional groups required to complete the synthesis.

The total synthesis of Isodon diterpenes.

Families of structurally related molecules often provide stimulating targets for organic chemists that are engaged in the development of new methods and strategies for natural product synthesis. While typically focused on specific molecules, these synthetic investigations often lead to generalizable concepts and significant opportunities for learning in a greater sense. Historically well-investigated families of natural products, such as the prostanoids, indole alkaloids, and macrolide antibiotics, provide ample evidence for the enduring value of these collective activities. In this Minireview, we turn our attention to the polycyclic family of diterpenes isolated from the Isodon genus of plants and provide an account of the recent methods and strategies utilized for their total synthesis.

Evaluation of 'east-to-west' ether-forming strategies for the total synthesis of maoecrystal V.

Model systems that evaluated different approaches to construct the central ether ring of maoecrystal V are described. Our first model systems attempted the ether formation using C-H functionalization reactions, which led to interesting rearrangements but none of the desired ether product. An intramolecular conjugate addition strategy was then explored that successfully formed the targeted C-O bond but resulted in the undesired stereochemistry.

Enantioselective total synthesis and confirmation of the absolute and relative stereochemistry of streptorubin B.

The enantioselective total synthesis of the pyrrolophane natural product streptorubin B is described. Key steps in the concise route include the application of a one-pot enantioselective aldol cyclization/Wittig reaction and an anionic oxy-Cope rearrangement to forge the crucial 10-membered ring. Comparisons between CD spectra of synthetic and natural samples of streptorubin B coupled with X-ray crystallography allowed for the determination of the absolute stereochemistry of this natural product for the first time. These studies also provided unambiguous proof of the relative configuration between the butyl side chain and the bispyrrole subunit. Additional studies revealed a novel atropstereoselective Paal-Knorr pyrrole condensation and provided fundamental experimental insight into the barrier for atropisomerization of the natural product.

A synthesis of the carbocyclic core of maoecrystal V.

An approach toward the synthesis of the complex polycyclic diterpene maoecrystal V (1) is described. Construction of the advanced tetracyclic core structure (i.e., 19) was achieved in 13 steps from 3,3-dimethylcyclohexanone (6) by employing a stereoselective Nazarov cyclization followed by a Diels-Alder reaction to forge the two contiguous quaternary stereocenters.