A new synthetic method produces a bioresponsive near-infrared molecular probe that undergoes “turn-on” fluorescence for microscopic imaging of hypoxia.

The bimetallic organomagnesiate ate complex (S)‐(BIPHEN)BuMgLi is reported here as a dual efficient halogen‐metal exchange and chirality transfer agent in the reaction of ethyl‐2‐iodobenzoate with aldehydes leading to the formation of various chiral 3‐substituted isobenzofuranones in good yields and enantiomeric ratios.

Two new classes of near‐infrared molecular probes were prepared and shown to exhibit “turn on” fluorescence when cleaved by the nitroreductase enzyme, a well‐known biomarker of cell hypoxia. The fluorescent probes are heptamethine cyanine dyes with a central 4‘‐carboxylic ester group on the heptamethine chain that is converted by a self‐immolative fragmentation mechanism to a 4‘‐caboxylate group that greatly enhances the fluorescence brightness. Each compound was prepared by ring opening of a Zincke salt. The chemical structures have either terminal benzoindolinenes or propargyloxy auxochromes, which provide favorable red‐shifted absorption/emission wavelengths and a hyperchromic effect that enhances the photon output when excited by 808 nm light. A fluorescent probe with terminal propargyloxy‐indolenines exhibited less self‐aggregation and was rapidly activated by nitroreductase with large “turn on“ fluorescence; thus, it is the preferred choice for translation towards in vivo applications.

Two new azobenzene heptamethine cyanine conjugates exist as dispersed monomeric molecules in methanol solution and exhibit near-infrared (NIR) cyanine absorption and fluorescence. Both conjugates form non-emissive cyanine H-aggregates in water, but the addition of cucurbit[7]uril (CB7) induces dye deaggregation and a large increase in cyanine NIR fluorescence emission intensity. CB7 encapsulates the protonated azonium tautomer of the 4-(N,N-dimethylamino)azobenzene component of each azobenzene–cyanine conjugate and produces a distinctive new absorption band at 534 nm. The complex is quite hydrophilic, which suggests that CB7 can be used as a supramolecular additive to solubilize this new family of NIR azobenzene–cyanine conjugates for future biomedical applications. Since many azobenzene compounds are themselves potential drug candidates or theranostic agents, it should be possible to formulate many of them as CB7 inclusion complexes with improved solubility, stability, and pharmaceutical profile.

The Front Cover illustrates the action of a cyanine‐based fluorescent probe inside a hypoxic A549 cell. Nitroreductase enzyme, a well‐known biomarker of hypoxia, transforms a carboxylic ester group on the central heptamethine chain through a self‐immolative fragmentation mechanism into a brightly fluorescent carboxylate group, resulting in a “turn on” fluorescent response. The cell elements were provided by Reactome.org under the CC BY 4.0 license. More information can be found in the Research Article by P. Štacko, B. D. Smith et al.