Katsunori Tanaka

Pyrene excimer-based fluorescent probes for chemoselective detection of acrolein have been developed by leveraging a [4+4] cycloaddition dimerization between unsaturated aldehydes and 1,2-amino alcohol derivatives. Building on our previously reported Probe A, which features an ethanolamine skeleton and a pyrene fluorophore, we designed and synthesized a series of second-generation probes (Probes B–E) that report acrolein binding through pyrene excimer emission. Using serine- and glycine-derived building blocks, we established concise synthetic routes that enable facile preparation of these probes in high overall yields. We identified optimized cycloaddition dimerization conditions under which a small amount of acetic acid promotes conjugated imine formation and affords a rapid and pronounced increase in excimer fluorescence. Reactivity studies with a panel of α,β-unsaturated aldehydes revealed that, compared with the first-generation probe bearing a terminal primary amine, second-generation 1,2-amino alcohol probes in which the primary amine is located at an internal secondary carbon exhibit enhanced chemoselectivity for acrolein while maintaining favorable sensitivity. We further optimized extraction and reaction conditions for Probe D and demonstrated quantitative detection of cell-derived acrolein by monitoring acrolein concentration-dependent excimer fluorescence in organic extracts from hydrogen peroxide–treated RAW264.7 cells.

Synthetic chemistry within living systems offers a transformative strategy for precision medicine by enabling the targeted generation of therapeutic agents directly at disease sites. Carbon monoxide (CO), an endogenous gasotransmitter upregulated in many cancer phenotypes, represents a unique yet underexploited chemical feedstock for such intracellular synthesis. However, the intrinsically low reactivity of CO necessitates transition-metal mediation, which is typically compromised by rapid deactivation by intracellular thiols such as glutathione (GSH). Here, we present a biocompatible albumin-palladacycle complex (APC) platform that harnesses endogenous CO for two distinct functions: the detection of CO levels and the in situ synthesis of cytotoxic phenanthridinone derivatives—a privileged scaffold found in potent poly(ADP-ribose) polymerase (PARP) and topoisomerase inhibitors. Central to this design is a coumarin anchor that directs the palladium center into the hydrophobic binding pocket of albumin, shielding it from thiol-mediated poisoning while facilitating cellular uptake via endocytosis. We demonstrate that this system effectively detects elevated CO in cancer cells and, in a parallel application, enables the in situ synthesis of pharmacologically active agents. Although the associated cytotoxicity is modest, the approach nonetheless suppresses cancer cell growth. This study considerably advances the proof of concept for “therapeutic in vivo synthetic chemistry,” in which disease-associated metabolites are repurposed as structural building blocks for both diagnostic and therapeutic applications.

The difructose dianhydride I synthase/hydrolase catalyzes the reversible transformation of inulobiose into difructose dianhydride I, a component of caramel. The proposed reaction mechanism of such a transformation consists of a glycosylation step followed by a cyclization to yield the dianhydride from the disaccharide. Here, we make use of extensive hybrid QM/MM metadynamics studies to shed light on the molecular basis of it. Our simulations show that the global reaction for the transformation of inulobiose by is slightly exergonic in good agreement with the experimental data. Furthermore, we observe that the glycosylation step is the rate‐limiting step. Interestingly, our work shows that the –1 sugar of inulobiose changes from an initial E conformation into a E puckering via the conformational pathway E E / T E E . Our calculations highlight that in the cyclization step, the three residues E85, K147, and N226 are essential for the rotation of the +1 sugar in the substrate to facilitate the intramolecular attack of oxygen O1' to the anomeric carbon. Prompted by these results, we expressed and assayed the N226A variant. Enzyme activity data confirm an important role for N226 during the cyclization step but show that it is dispensable for the hydrolysis step.

Acrolein is the simplest α,β-unsaturated aldehyde, and its selective hydrogenation on metal surfaces is of fundamental interest. Here, we investigate the adsorption structures of acrolein molecules on Cu(111) by scanning tunneling microscopy. At low temperatures, chemisorbed and physisorbed monomers as well as dimers are observed. The thermally most stable chemisorbed monomer is assigned to 12 symmetry-equivalent adsorption orientations on Cu(111). The observed asymmetry between the C=C and C=O groups provides microscopic insight into the adsorption geometries relevant to selective hydrogenation.

Chemotherapy lacks specificity, resulting in significant side effects on healthy tissues. Although molecularly targeted therapies have become standard treatments instead of chemotherapy, cancer heterogeneity hinders their effectiveness, and the availability of targeted antigens in clinical samples remains limited. Cell surface glycans have various "glycan patterns" composed of different glycan molecules, facilitating strong and selective cell-to-cell recognition. To better understand the factors influencing glycan pattern recognition in vivo, we created artificial glycoalbumins and identified cancer-specific accumulation patterns for various glycoalbumins modified with specific glycan patterns. To leverage the insights gained from these studies, we used glycoalbumin scaffolds as glycosylated therapeutic artificial metalloenzymes for cancer treatment by localizing their biological activity to avoid unwanted side effects. This review presents our foundational research that has driven artificial glycoalbumin-based targeting and subsequent adaptations for potential therapeutic applications.

Zwitterionic heterocycles hold significant therapeutic potential; however, their application is often hindered by poor membrane permeability and limited target‐cell selectivity. Here, we report an innovative strategy for the in situ synthesis of these compounds within cancer cells, using a rationally designed precursor that is nontoxic, non‐ionic, and membrane permeable. The synthesis is initiated by endogenous acrolein, an oncometabolite elevated in cancer cells, which triggers a cascade involving 1,3‐dipolar cycloaddition, diazo formation, carbamate cleavage, imine formation, intramolecular 6π‐azaelectrocyclization, oxidative aromatization, and ester hydrolysis. We validated this methodology in human lung adenocarcinoma (A549) cells, where the in situ‐synthesized zwitterionic heterocycle exhibited anticancer activity. Conversely, its pre‐synthesized congener showed minimal cytotoxicity, underscoring the poor membrane permeability of the zwitterionic form. Precursor optimization resulted in a lead compound that, upon administration to A549 cells, converted into a cytotoxic zwitterionic heterocycle with a half‐maximal inhibitory concentration (IC ₅₀ ) of 6.2 µM. The lead precursor showed exceptional selectivity, with no cytotoxicity in normal human diploid (TIG3) cells. This selectivity arises because healthy cells contain low acrolein levels, insufficient to trigger the activation cascade. Our approach effectively addresses the key therapeutic challenges associated with zwitterionic heterocycles.

Zwitterionic heterocycles hold significant therapeutic potential; however, their application is often hindered by poor membrane permeability and limited target‐cell selectivity. Here, we report an innovative strategy for the in situ synthesis of these compounds within cancer cells, using a rationally designed precursor that is nontoxic, non‐ionic, and membrane permeable. The synthesis is initiated by endogenous acrolein, an oncometabolite elevated in cancer cells, which triggers a cascade involving 1,3‐dipolar cycloaddition, diazo formation, carbamate cleavage, imine formation, intramolecular 6π‐azaelectrocyclization, oxidative aromatization, and ester hydrolysis. We validated this methodology in human lung adenocarcinoma (A549) cells, where the in situ‐synthesized zwitterionic heterocycle exhibited anticancer activity. Conversely, its pre‐synthesized congener showed minimal cytotoxicity, underscoring the poor membrane permeability of the zwitterionic form. Precursor optimization resulted in a lead compound that, upon administration to A549 cells, converted into a cytotoxic zwitterionic heterocycle with a half‐maximal inhibitory concentration (IC ₅₀ ) of 6.2 µM. The lead precursor showed exceptional selectivity, with no cytotoxicity in normal human diploid (TIG3) cells. This selectivity arises because healthy cells contain low acrolein levels, insufficient to trigger the activation cascade. Our approach effectively addresses the key therapeutic challenges associated with zwitterionic heterocycles.

The intracellular polymerization of synthetic macromolecules presents a unique method for modifying cell behavior, enabling real‐time imaging, and enhancing therapeutic effectiveness. However, most current strategies rely on external catalysts or non‐physiological triggers, often lacking target‐cell specificity. Here, we report a cancer‐selective intracellular cyclodimerization cascade polymerization driven solely by endogenous acrolein, an oncometabolite overproduced in malignant cells. Acrolein plays dual roles as a polymerization initiator through imine formation and as a structural component of the resulting polymer. We designed a meta ‐phenylene‐bis(2‐aminoethanol) monomer that incorporates an aggregation‐induced emission (AIE)‐active tetraphenylethylene unit. In acrolein‐rich cancer cells, condensation between the aminoethanol groups and acrolein generates imines, which then undergo a spontaneous, catalyst‐free cyclodimerization cascade, yielding eight‐membered 1,5‐diazacyclooctane polymers that embed native acrolein. This polymerization triggers robust AIE fluorescence “turn‐on”, facilitating high‐contrast imaging of malignant cells with minimal background in healthy cells. We demonstrated selective fluorescence in multiple cancer cell lines and applied this platform to freshly resected human breast tumor samples, showing its utility for rapid intraoperative assessment. This strategy establishes a versatile toolkit for precision diagnostics, engineered intracellular materials, and next‐generation therapeutics.

The intracellular polymerization of synthetic macromolecules presents a unique method for modifying cell behavior, enabling real‐time imaging, and enhancing therapeutic effectiveness. However, most current strategies rely on external catalysts or non‐physiological triggers, often lacking target‐cell specificity. Here, we report a cancer‐selective intracellular cyclodimerization cascade polymerization driven solely by endogenous acrolein, an oncometabolite overproduced in malignant cells. Acrolein plays dual roles as a polymerization initiator through imine formation and as a structural component of the resulting polymer. We designed a meta ‐phenylene‐bis(2‐aminoethanol) monomer that incorporates an aggregation‐induced emission (AIE)‐active tetraphenylethylene unit. In acrolein‐rich cancer cells, condensation between the aminoethanol groups and acrolein generates imines, which then undergo a spontaneous, catalyst‐free cyclodimerization cascade, yielding eight‐membered 1,5‐diazacyclooctane polymers that embed native acrolein. This polymerization triggers robust AIE fluorescence “turn‐on”, facilitating high‐contrast imaging of malignant cells with minimal background in healthy cells. We demonstrated selective fluorescence in multiple cancer cell lines and applied this platform to freshly resected human breast tumor samples, showing its utility for rapid intraoperative assessment. This strategy establishes a versatile toolkit for precision diagnostics, engineered intracellular materials, and next‐generation therapeutics.