Development of a General Organophosphorus Radical Trap: Deoxyphosphonylation of Alcohols.

Here we report the design of a general, redox-switchable organophosphorus alkyl radical trap that enables the synthesis of a broad range of C(sp3)-P(V) modalities. This "plug-and-play" approach relies upon in situ activation of alcohols and O═P(R2)H motifs, two broadly available and inexpensive sources of molecular complexity. The mild, photocatalytic deoxygenative strategy described herein allows for the direct conversion of sugars, nucleosides, and complex pharmaceutical architectures to their organophosphorus analogs. This includes the facile incorporation of medicinally relevant phosphonate ester prodrugs.

Metallaphotoredox: The Merger of Photoredox and Transition Metal Catalysis.

The merger of photoredox catalysis with transition metal catalysis, termed metallaphotoredox catalysis, has become a mainstay in synthetic methodology over the past decade. Metallaphotoredox catalysis has combined the unparalleled capacity of transition metal catalysis for bond formation with the broad utility of photoinduced electron- and energy-transfer processes. Photocatalytic substrate activation has allowed the engagement of simple starting materials in metal-mediated bond-forming processes. Moreover, electron or energy transfer directly with key organometallic intermediates has provided novel activation modes entirely complementary to traditional catalytic platforms. This Review details and contextualizes the advancements in molecule construction brought forth by metallaphotocatalysis.

µMap-Red: Proximity Labeling by Red Light Photocatalysis.

Modern proximity labeling techniques have enabled significant advances in understanding biomolecular interactions. However, current tools primarily utilize activation modes that are incompatible with complex biological environments, limiting our ability to interrogate cell- and tissue-level microenvironments in animal models. Here, we report µMap-Red, a proximity labeling platform that uses a red-light-excited SnIV chlorin e6 catalyst to activate a phenyl azide biotin probe. We validate µMap-Red by demonstrating photonically controlled protein labeling in vitro through several layers of tissue, and we then apply our platform in cellulo to label EGFR microenvironments and validate performance with STED microscopy and quantitative proteomics. Finally, to demonstrate labeling in a complex biological sample, we deploy µMap-Red in whole mouse blood to profile erythrocyte cell-surface proteins. This work represents a significant methodological advance toward light-based proximity labeling in complex tissue environments and animal models.

Decatungstate-Catalyzed C(sp3)-H Sulfinylation: Rapid Access to Diverse Organosulfur Functionality.

Here we report the direct conversion of strong, aliphatic C(sp3)-H bonds into the corresponding alkyl sulfinic acids via decatungstate photocatalysis. This transformation has been applied to a diverse range of C(sp3)-rich scaffolds, including natural products and approved pharmaceuticals, providing efficient access to complex sulfur-containing products. To demonstrate the broad potential of this methodology for the divergent synthesis of pharmaceutically relevant molecules, procedures for the diversification of the sulfinic acid products into a range of medicinally relevant functional groups have been developed.

Design of a Multiuse Photoreactor To Enable Visible-Light Photocatalytic Chemical Transformations and Labeling in Live Cells.

Despite the growing use of visible-light photochemistry in both chemistry and biology, no general low-heat photoreactor for use across these different disciplines exists. Herein, we describe the design and use of a standardized photoreactor for visible-light-driven activation and photocatalytic chemical transformations. Using this single benchtop photoreactor, we performed photoredox reactions across multiple visible light wavelengths, a high-throughput photocatalytic cross-coupling reaction, and in vitro labeling of proteins and live cells. Given the success of this reactor in all tested applications, we envision that this multi-use photoreactor will be widely used in biology, chemical biology, and medicinal chemistry settings.

C-H Functionalization of Heteroarenes Using Unactivated Alkyl Halides through Visible-Light Photoredox Catalysis under Basic Conditions.

C-H functionalization of electron-deficient heteroarenes using commercial unactivated alkyl halides through reductive quenching photoredox catalysis was developed. Mainstream approaches rely on the use of an excess of strong acids that result in regioselectivities dictated by the innate effect of the protonated heteroarene, leaving the functionalization of other carbons unexplored. We report a mild method under basic conditions that allows access to previously underexplored regioselectivities by relying on a combination of conjugate and halogen  ortho-directing effects. Overall, this methodology gives quick access to a variety of alkylated heteroarenes that will be of interest to medicinal chemistry programs.

Interrogating biological systems using visible-light-powered catalysis.

Light-powered catalysis has found broad utility as a chemical transformation strategy, with widespread impact on energy, environment, drug discovery and human health. A noteworthy application impacting human health is light-induced sensitization of cofactors for photodynamic therapy in cancer treatment. The clinical adoption of this photosensitization approach has inspired the search for other photochemical methods, such as photoredox catalysis, to influence biological discovery. Over the past decade, light-mediated catalysis has enabled the discovery of valuable synthetic transformations, propelling it to become a highly utilized chemical synthesis strategy. The reaction components required to achieve a photoredox reaction are identical to photosensitization (catalyst, light source and substrate), making it ideally suited for probing biological environments. In this Review, we discuss the therapeutic application of photosensitization and advancements made in developing next-generation catalysts. We then highlight emerging uses of photoredox catalytic methods for protein bioconjugation and probing complex cellular environments in living cells.

Expedient access to saturated nitrogen heterocycles by photoredox cyclization of imino-tethered dihydropyridines.

A large proportion of medicinally relevant molecules bear nitrogen and sp3-hybridized carbon functionalities. Overwhelmingly, these atoms are found as part of (hetero)cyclic structures. Despite their importance, synthetic approaches to saturated nitrogen heterocycles are limited to several established stoichiometric alkylation techniques, as well as a few methods involving C-H bond activation. The synthetic community remains interested in more general, mild, and sustainable ways to access these motifs. Here we describe a dual-catalyst system composed of an iridium photocatalyst and a lithium phosphate base that is capable of selectively homolyzing the N-H bond of 4-alkyl-1,4-dihydropyridines, presumably by proton-coupled-electron-transfer (PCET), and mediating efficient cyclization of the resultant carbon-centered radicals with tethered imines. The outcome of this transformation is access to a broad range of structurally complex nitrogen heterocycles obtainable from simple aldehyde starting materials in a highly chemoselective manner.