Chiral phosphoric acids (CPAs) have emerged as powerful organocatalysts for asymmetric reactions, and applications of computational quantum chemistry have revealed important insights into the activity and selectivity of these catalysts. In this tutorial review, we provide an overview of computational tools at the disposal of computational organic chemists and demonstrate their application to a wide array of CPA catalysed reactions. Predictive models of the stereochemical outcome of these reactions are discussed along with specific examples of representative reactions and an outlook on remaining challenges in this area.

Supporting information for this article is given via a link at the end of the document.

In the context of deep-tissue disease biomarker detection and analyte sensing of biologically relevant species, the impact of photoacoustic imaging has been profound. However, most photoacoustic imaging agents to date are based on the repurposing of existing fluorescent dye platforms that exhibit non-optimal properties for photoacoustic applications (e.g., high fluorescence quantum yield). Herein, we introduce two effective modifications to the hemicyanine dye to afford PA-HD, a new dye scaffold optimized for photoacoustic probe development. We observed a significant increase in the photoacoustic output, representing an increase in sensitivity of 4.8-fold and a red-shift of the λ abs from 690 nm to 745 nm to enable ratiometric imaging.Moreover, to demonstrate the generalizability and utility of our remodeling efforts, we developed three probes using common analyte-responsive triggers for beta-galactosidase activity (PA-HD-Gal), nitroreductase activity (PA-HD-NTR), and hydrogen peroxide (PA-HD-H 2 O 2 ). The performance of each probe (responsiveness, selectivity) was evaluated in vitro and in cellulo. To showcase the enhance properties afforded by PA-HD for in vivo photoacoustic imaging, we employed an Alzheimer's disease model to detect H 2 O 2 . In particular, the photoacoustic signal at 735 nm in the brains of 5xFAD mice (a murine model of Alzheimer's disease) increased by 1.72 ± 0.20-fold relative to background indicating the presence of oxidative stress, whereas the change in wildtype mice was negligible (1.02 ± 0.14). These results were confirmed via ratiometric calibration which was not possible using the parent HD platform. File list (2)download file view on ChemRxiv ChemRxiv PA-HD SI FINAL.pdf (1.22 MiB) download file view on ChemRxiv ChemRxiv PA-HD Manuscript FINAL.pdf (806.53 KiB)

Selective functionalization of aliphatic C–H bonds, ubiquitous in molecular structures, could allow ready access to diverse chemical products. While enzymatic oxygenation of C–H bonds is well established, the analogous enzymatic nitrogen functionalization is still unknown; nature is reliant on preoxidized compounds for nitrogen incorporation. Likewise, synthetic methods for selective nitrogen derivatization of unbiased C–H bonds remain elusive. In this work, new-to-nature heme-containing nitrene transferases were used as starting points for the directed evolution of enzymes to selectively aminate and amidate unactivated C­(sp3)–H sites. The desymmetrization of methyl- and ethylcyclohexane with divergent site selectivity is offered as demonstration. The evolved enzymes in these lineages are highly promiscuous and show activity toward a wide array of substrates, providing a foundation for further evolution of nitrene transferase function. Computational studies and kinetic isotope effects (KIEs) are consistent with a stepwise radical pathway involving an irreversible, enantiodetermining hydrogen atom transfer (HAT), followed by a lower-barrier diastereoselectivity-determining radical rebound step. In-enzyme molecular dynamics (MD) simulations reveal a predominantly hydrophobic pocket with favorable dispersion interactions with the substrate. By offering a direct path from saturated precursors, these enzymes present a new biochemical logic for accessing nitrogen-containing compounds.

Axially chiral cyclohexylidene oxime ethers exhibit unique chirality because of the restricted rotation of C=N. The first catalytic enantioselective synthesis of novel axially chiral cyclohexylidene oximes has been developed by catalytic desymmetrization of 4-substituted cyclohexanones with O-arylhydroxylamines and is catalyzed by a chiral BINOL-derived strontium phosphate with excellent yields and good enantioselectivities. In addition, chiral BINOL-derived phosphoric acid catalyzed dynamic kinetic resolution of α-substituted cyclohexanones has been performed and yields versatile intermediates in high yields and enantioselectivities.

The enantioselective synthesis of a broad variety of novel differently functionalized α-halogenated α-aryl-β 2,2 -amino acid derivatives by means of an ammonium-salt-catalyzed asymmetric α-halogenation of isoxazolidin-5-ones was accomplished. Key to success to obtain high levels of enantioselectivities was the use of Maruoka’s spirocyclic binaphthyl-based ammonium salts, and detailed accompanying mechanistic studies using density functional theory methods revealed the key features for the catalyst–substrate interactions.

SWIR dyes offer many advantages over their more common NIR congeners; however, the available options are limited. New SWIR imaging agents can be accessed by remodeling existing NIR molecules (i.e., hemicyanines (HDs)). In this study, we synthesized SWIR-HD, a modified HD featuring dimethylsilicon and benzo[cd]indolium groups that are designed to red-shift the absorbance and emission to 988 and 1126 nm, respectively. SWIR-HD was employed to visualize the liver and tumors via multimodal SWIR imaging.

In the context of deep-tissue disease biomarker detection and analyte sensing of biologically relevant species, the impact of photoacoustic imaging has been profound. However, most photoacoustic imaging agents to date are based on the repurposing of existing fluorescent dye platforms that exhibit non-optimal properties for photoacoustic applications (e.g., high fluorescence quantum yield). Herein, we introduce two effective modifications to the hemicyanine dye to afford PA-HD, a new dye scaffold optimized for photoacoustic probe development. We observed a significant increase in the photoacoustic output, representing an increase in sensitivity of 4.8-fold and a red-shift of the λ abs from 690 nm to 745 nm to enable ratiometric imaging.Moreover, to demonstrate the generalizability and utility of our remodeling efforts, we developed three probes using common analyte-responsive triggers for beta-galactosidase activity (PA-HD-Gal), nitroreductase activity (PA-HD-NTR), and hydrogen peroxide (PA-HD-H 2 O 2 ). The performance of each probe (responsiveness, selectivity) was evaluated in vitro and in cellulo. To showcase the enhance properties afforded by PA-HD for in vivo photoacoustic imaging, we employed an Alzheimer's disease model to detect H 2 O 2 . In particular, the photoacoustic signal at 735 nm in the brains of 5xFAD mice (a murine model of Alzheimer's disease) increased by 1.72 ± 0.20-fold relative to background indicating the presence of oxidative stress, whereas the change in wildtype mice was negligible (1.02 ± 0.14). These results were confirmed via ratiometric calibration which was not possible using the parent HD platform. File list (2)download file view on ChemRxiv ChemRxiv PA-HD SI FINAL.pdf (1.22 MiB) download file view on ChemRxiv ChemRxiv PA-HD Manuscript FINAL.pdf (806.53 KiB)