The long-chain aliphatic-group-substituted mandelic acid 3c, which is soluble only in THF and insoluble in water and many polar/nonpolar organic solvents, has been synthesized. This unique solubility allows 3c to be easily isolated from reaction mixtures and makes it potentially useful for catalyst screening. The fluorescent sensors (R)- and (S)-1 can be used to determine the ees of various samples of 3c generated from a series of catalyst screening experiments. The fluorescence measurements correlate well with the conventional HPLC-chiral column analysis. This work demonstrates that the enantioselective fluorescent recognition of organic substrates can lead to a fundamentally new method for chiral catalyst screening. [reaction: see text]
The intramolecular exo-cycloaddition reaction between N,N-dimethylthioacrylamide and 3,4-dimethyl-1phenylphosphole in the presence of a perchloratopalladium template containing ortho-metallated (S)-(1-(dimethylamino)ethyl)naphthalene as the chiral auxiliary gave the corresponding thioamide-substituted P-chiral phosphanorbornene stereospecifically in 6 d. The exo-cycloadduct coordinated to the palladium template as a bidentate chelate via its phosphorus and thioamide-sulfur donor atoms. The corresponding intermolecular endo-cycloaddition reaction using the analogous chloropalladium template containing the same ortho-metallated naphthylamine auxiliary produced a pair of separable diastereomeric endocycloadducts in 60 d. Both the endo-cycloadducts coordinated to the palladium template as monodentates via their phosphorus donor atoms and their thioamide functions were not involved in the metal complexation. The faster rate observed in the exo-cycloaddition reaction is attributed to the electronic polarization and hence the activation of N,N-dimethylthioacrylamide via thioamide-S coordination. Optically active thioamide-substituted phosphanorbornenes could be liberated from these product complexes by treatment with aqueous cyanide. For comparison purposes, the novel ligand Ph 2 PC(S)NMe 2 was prepared. This short-chain ligand displaced acetonitrile and monodentate phosphine ligands on Pd II to form stable 4-membered P-S chelates. The C᎐ ᎐ S bond in these sterically hindered chelates are unreactive toward cycloaddition reaction with the phosphole cyclic diene. The thioamido (S)C-N bonds in this series of P-S palladium() chelates were found to be significantly shorter than those reported for organic thioamides and their non-chelating counterparts in the endo-cycloadducts, thus indicating that nitrogen in the thioamide function contributed electronically to the stability of the Pd→S bonds.
Viral encephalitis is an inflammatory disease of the brain parenchyma and caused by various viral infections. In vivo monitoring of the progression of viral infections can aid accurate diagnosis of viral encephalitis and effective intervention. We developed an activatable and reversible virus-mimicking near-infrared II nanoprobe consisting of an Fe 2 + -coordinated, viral proteindecorated vesicle encapsulating PbS quantum dots with a 1300 nm fluorescence emission. The probe can cross the blood-brain barrier and monitor real-time changes in reactive oxygen and nitrogen species concentrations during viral infection by tuning the quenching level of quantum dots and regulating the fusion-fission behavior of vesicles via changes in Fe oxidation state. This switching strategy reduces background noise and improves detection sensitivity, making this nanoprobe a promising imaging agent for dynamic visualization of viral encephalitis and future clinical applications.
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