Biosensors for ultrasensitive point-of-care testing require dried reagents with long-term stability and a high signal-to-background ratio. Although ortho-substituted diaromatic dihydroxy and aminohydroxy compounds undergo fast redox reactions, they are not used as electrochemical signaling species because they are readily oxidized and polymerized by dissolved oxygen. In this report, stable, solid 1-amino-2-naphthyl phosphate (1A2N-P) and ammonia-borane (HN-BH) are respectively employed as a substrate for alkaline phosphatase (ALP) and a reductant for electrochemical-chemical (EC) redox cycling. ALP converts 1A2N-P to 1-amino-2-naphthol (1A2N), which is then employed in EC redox cycling using HN-BH. The oxidation and polymerization of 1A2N by dissolved oxygen is significantly prevented in the presence of HN-BH. The electrochemical measurement is performed without modification of indium-tin oxide (ITO) electrodes with electrocatalytic materials. For comparison, nine aromatic dihydroxy and aminohydroxy compounds, including 1A2N, are evaluated to achieve fast EC redox cycling, and four strong reductants, including HN-BH, are evaluated to achieve a low background level. The combination of 1A2N and HN-BH allows the achievement of a very high signal-to-background ratio. When the newly developed combination is applied to the detection of creatine kinase-MB (CK-MB), the detection limit for CK-MB is ∼80 fg/mL, indicating that the combination allows ultrasensitive detection. The concentrations of CK-MB in clinical serum samples, determined using the developed system, are in good agreement with the concentrations obtained using a commercial instrument. Thus, the use of stable, solid 1A2N-P and HN-BH along with bare ITO electrodes is highly promising for ultrasensitive and simple point-of-care testing.

Facile homo‐coupling of terminal alkynes, which generates conjugated diynes, is an undesired pathway in the development of transition‐metal‐catalyzed oxidative C–H functionalization of (hetero)arenes with terminal alkynes. By incorporating this process into a catalytic cycle, we achieved regio‐ and stereoselective hydroarylation of nitropyrazoles with the resulting 1,3‐diynes. A simple change in the stoichiometry and oxidant allowed direct C–H alkynylation of nitropyrazoles, producing the corresponding alkynyl pyrazoles.

DT-diaphorase (DT-D) is known to mainly catalyze the two-electron reduction of quinones and nitro­(so) compounds. Detection of Gram-negative bacterial outer membrane vesicles (OMVs) that contain pyrogenic lipopolysaccharides (LPSs, also called endotoxins) is required for evaluating the toxic effects of analytical samples. Here, we report that DT-D has a high dephosphorylation activity: DT-D catalyzes reductive dephosphorylation of a phosphate-containing substrate in the presence of NADH. We also report that sensitive and simple OMV detection is possible with a sandwich-type electrochemical immunosensor using DT-D and two identical LPS-binding antibodies as a catalytic label and two sandwich probes, respectively. The absorbance change in a solution containing 4-nitrophenyl phosphate indicates that dephosphorylation occurs in the presence of both DT-D and NADH. Among the three phosphate-containing substrates [4-aminophenyl phosphate, ascorbic acid phosphate, and 1-amino-2-naphthyl phosphate (ANP)] that can be converted into electrochemically active products after dephosphorylation, ANP shows the highest electrochemical signal-to-background ratio, because (i) the dephosphorylation of ANP by DT-D is fast, (ii) the electrochemical oxidation of the dephosphorylated product (1-amino-2-naphthol, AN) is rapid, even at a bare indium–tin oxide electrode, and (iii) two redox cycling processes significantly increase the electrochemical signal. The two redox cycling processes include an electrochemical–enzymatic redox cycling and an electrochemical–chemical redox cycling. The electrochemical signal in a neutral buffer (tris buffer, pH 7.5) is comparable to that in a basic buffer (tris buffer, pH 9.5). When the immunosensor is applied to the detection of OMV from Escherichia coli, the detection limit is found to be 8 ng/mL. This detection strategy is highly promising for the detection of biomaterials, including other extracellular vesicles.

We report a palladium‐catalyzed C‐2 allylation of indoles and subsequent cyclization of the allylated indoles. The electronic effects of chloro and ester groups that can be readily installed at the C‐3 position of indoles facilitated a highly efficient C–H allylation at the C‐2 position. The resulting 2‐allyl‐3‐chloroindoles were found to be suitable substrates for benzannulation reactions with alkynes and norbornadiene as an acetylene synthon. This approach, utilizing readily available indoles, allyl acetates, and norbornadiene, allows a rapid access to complex carbazoles.magnified image

Regioselective C4‐, C5‐, and di‐alkenylations of pyrazoles were achieved. An electrophilic Pd catalyst generated by trifluoroacetic acid (TFA) and 4,5‐diazafluoren‐9‐one (DAF) leads to C4‐alkenylation, whereas KOAc and mono‐protected amino acid (MPAA) ligand Ac‐Val‐OH give C5‐alkenylation. A combination of palladium acetate, silver carbonate, and pivalic acid affords dialkenylation products. Annulation through sequential alkenylation, thermal 6π‐electrocyclization, and oxidation gives functionalized indazoles. This comprehensive strategy greatly expands the range of readily accessible pyrazole and indazole derivatives, enabling useful regiodivergent C−H functionalization of pyrazoles and other heteroaromatic systems.