Kensuke Okuda

Many fluorescent recognition-based copper probes have been developed, but they generally suffer from a weak fluorescence change upon detection of low-abundance labile copper in biological systems. We have addressed this issue by developing an activity-based copper probe that recycles a portion of copper after detection, thereby amplifying the fluorescence signal. The probe showed good sensitivity and could be applied to in-cell experiments. We expect that similar systems will also be useful for the detection of other bioactive targets that exist at low concentrations.

Carbasugar-containing natural products such as uvaridacol L have a variety of bioactivities, motivating chemists to develop methods for their synthesis. The conversion of myo-inositol is one of the most efficient methods for the synthesis of carbasugars. However, selective conversion of myo-inositol derivatives remains to be explored. In our synthesis of uvaridacol L derivatives, we found that the methoxy olefin derivatives of orthoester-protected myo-inositols, the key synthetic intermediates of our study, exhibit differing reaction selectivities depending on their geometric isomerism and substituents. Here we present new insights that contribute to the synthesis of carbasugar-type derivatives by elucidating the mechanism of the selectivity using density functional theory (DFT) calculations.

The antiausterity strategy in anticancer drug discovery has attracted much attention as a way to exterminate cancer cells under nutrient deprived conditions which are commonly found in solid tumors. These tumors under low nutrient stress are known to be malignant and often resist conventional drug therapy. As a potential drug candidate, we focused on the meroterpenoid natural product callistrilone O which has demonstrated extremely potent antiausterity properties toward PANC‐1 pancreatic carcinoma in vitro. Here, we report for the first time the total synthesis of callistrilone O in seven steps from phloroglucinol. A Friedel‐Crafts‐type Michael addition and an oxidative [3+2] cycloaddition with Fetizon's reagent were used to construct the molecular skeleton. The preferential cytotoxicity of callistrilone O was also evaluated with multiple starvation‐resistant cancer cell lines under low nutrient conditions. Furthermore, callistrilone O was found to strongly suppress B16 melanoma tumor growth without critical toxicity in vivo. Overall, this study presents a novel anticancer agent candidate from natural products with a concise synthetic route which can be readily applied to the synthesis of derivatives.

A selective and quantitative OFF–ON fluorescent hydrazine probe was developed based on a coumarin platform. Elaboration of the β-keto moiety improved the responsiveness of the probe for sensing hydrazine in living cells.

One aspect of cancer-specific environments, nutrient starvation, is a factor in cancer cell resistance to treatment with chemotherapeutic agents and development of malignancy. Our newly synthesized novel glucose derivative β-1,3,6-O-tribenzoyl-D-glucose (3) showed preferential cytotoxicity against PANC-1 human pancreatic cancer cells as well as HT-29 human colon cancer cells depending on low nutritional environment. The amount of ester functionalization in 3 is important. None of the mono- and tetrabenzoylated D-glucose analog showed cytotoxicity, and dibenzoylated D-glucoses showed only limited cytotoxicity. Fluorescence imaging with double staining of Hoechst 33342 and propidium iodide clearly showed that 3 actually causes cell death in a nutrient deprived medium. We thus demonstrate that an inexpensive natural product, D-glucose, is a unique template for attachment of acyl moieties to target tolerance to nutrient starvation. We expect these compounds will lead to additional compounds to treat refractory cancers by diversification of chemically modified glucose.

Recently, the behavior of essential trace metal elements in living organisms has attracted more and more attention as their dynamics have been found to be tightly regulated by metallothionines, transporters, etc. As the physiological and/or pathological roles of such metal elements are critical, there have been many non-invasive methods developed to determine their cellular functions, mainly by small molecule fluorescent probes. In this review, we focus on probes that detect intracellular zinc and monovalent copper. Both zinc and copper act not only as tightly bound cofactors of enzymes and proteins but also as signaling factors as labile or loosely bound species. Many fluorescent probes that detect mobile zinc or monovalent copper are recognition-based probes, whose detection is hindered by the abundance of intracellular chelators such as glutathione which interfere with the interaction between probe and metal. In contrast, reaction-based probes release fluorophores triggered by zinc or copper and avoid interference from such intracellular chelators, allowing the detection of even low concentrations of such metals. Here, we summarize the current status of the cumulative effort to develop such reaction-based probes and discuss the strategies adopted to overcome their shortcomings.

The antiausterity natural product (±)-uvaridacol L was synthesized for the first time in seven steps from myo-inositol. The key reaction of this synthesis, axial selective dibenzoylation of myo-inositol orthoformate, was achieved using a catalytic amount of tetrabutylammonium fluoride (TBAF). The preferential cytotoxicity of racemic uvaridacol L against cancer cell lines able to adapt to nutrient deprivation was also evaluated under nutrient deprived conditions. Morphological evaluation was also carried out.

A reaction-based fluorescent probe with cephem scaffold has been applied for signal amplification system to detect trace intracellular zinc.