Studying the reactivity of alkyl substituted BODIPYs: first enantioselective addition of BODIPY to MBH carbonates

Catalytic asymmetric defluorinative allylation of silyl enol ethers

The stereocontrolled installation of alkyl fragments at the alpha position of ketones is a fundamental yet unresolved transformation in organic chemistry. Herein we report a new catalytic methodology able to construct α-allyl ketones via defluorinative allylation of silyl enol ethers in a regio-, diastereo- and enantioselective manner. The protocol leverages the unique features of the fluorine atom to simultaneously act as a leaving group and to activate the fluorophilic nucleophile via a Si-F interaction. A series of spectroscopic, electroanalytic and kinetic experiments demonstrate the crucial interplay of the Si-F interaction for successful reactivity and selectivity. The generality of the transformation is demonstrated by synthesising a wide set of structurally diverse α-allylated ketones bearing two contiguous stereocenters. Remarkably, the catalytic protocol is amenable for the allylation of biologically significant natural products.

Preferential solvation of meso-methyl BODIPYs with pyridine via pseudo-hydrogen-bonds

This study explored unexpected pseudo-hydrogen bond interactions between meso-methyl BODIPYs and pyridine or acridine. NMR spectral evidence indicated that the meso-methyl group and BF₂ core of BODIPYs formed C-H⋯N and C-H⋯F-B pseudo-hydrogen bonds with pyridine, respectively. The weak binding strength was attributed to the preferential solvation of pyridine in the vicinity of meso-methyl BODIPYs in cyclohexane. The observations were explained by the formation of pseudo-hydrogen bonds based on the quantum theory of atoms in molecules (QTAIM) formalism. In contrast, acridine binds to BODIPY with a moderate binding strength. QTAIM formalism suggested the existence of the complementary pseudo-hydrogen bonds, which superficially seemed to rationalise the experimental observations. However, extensive NMR experiments have found no discrete geometry for the complex, indicating considerable geometric freedom. This discrepancy suggests that the static pictures based on the QTAIM analyses conflict with the enthalpy-entropy compensation principle in essential thermodynamics.

A nitroreductase responsive and photoactivated fluorescent probe for dual-controlled tumor hypoxia imaging

Tumor hypoxia has great importance in tumor progression and resistance to antitumor therapies. To precisely monitor tumor hypoxia, a controllable hypoxia imaging method is meaningful but still lacking. Herein, we develop a dual-controlled tumor hypoxia probe (TNB) by introducing a nitrophenol group and methyltetrazine group to the boron-dipyrromethene (BODIPY) dye. The fluorescence-quenching group nitrophenol is reduced to aminophenol by upregulated nitroreductase in hypoxic tumors, and the photocage methyltetrazine is cleaved by light irradiation. Hence the fluorescence of TNB is dual-controlled by hypoxia and photoactivation. We first evaluated TNB's potential for controllable hypoxia imaging in solution and tumor cells. The fluorescence of TNB under nitroreductase incubation and photoactivation increased more than 60 fold over that which was untreated or only treated with nitroreductase. Furthermore, results validate that TNB possesses photo-controllable activation features in tumor sections. We believe that the probe design based on enzyme and photoactivation responsiveness provides potential for spatiotemporal detection of other biomarkers.

Tumor hypoxia has great importance in tumor progression and resistance to antitumor therapies.