A diverse range of o-arylthio-substituted diaryl ethers has been synthesized by direct oxythiolation of arynes with diaryl sulfoxides that involves the formation of the C–O and C–S bonds followed by migratory O-arylation.

A facile synthetic method for unsymmetrical tertiary phosphine oxides is reported. Sequential treatment of phosphonodithioic acid S,S-di(p-tolyl) esters with two Grignard reagents enabled the stepwise introduction of different carbon substituents on the phosphorus atom. The chemical stability of dithioesters and monosubstituted thioesters has enhanced the utility of this method, rendering a wide range of organophosphorus compounds easily available.

Treatment of benzocyclobutenones bearing a triflyloxy group adjacent to the four-membered ring with organolithium reagents in the presence of arynophiles efficiently affords three-component coupled α-arylketones. Mechanistic studies indicate that the reaction is promoted by generation of the aryne via carbon–carbon bond cleavage of a benzocyclobutenoxide intermediate, which led us to find a fluoride-mediated aryne generation method from triflyloxy-substituted benzocyclobutenone silyl acetal precursors.

Various diaryl sulfides, including heteroaryl- and nitrogen-containing sulfides, have been efficiently prepared by rhodium-catalyzed odorless deborylative arylthiolation of organoborons with S-aryl thiosulfonates. The ready availability of starting materials and further transformation of sulfides have rendered a diverse range of organosulfur compounds easily accessible.

A facile synthetic method for preparing 3-amino-2-silylaryl triflates via regioselective silylamination of 3-(triflyloxy)arynes with N-silylamines is described. Fluoride-mediated generation of 3-aminobenzyne from 3-amino-2-silylphenyl triflate, easily prepared by this method, in the presence of various arynophiles efficiently afforded diverse aniline derivatives, including a 5-aminocoumarin derivative, demonstrating the utility of aryne relay approach.

The blood–brain barrier permeability of ginkgolide B was examined using positron emission tomography (PET) probes of a 18F-incorporated ginkgolide B ([18F]-2) and a 11C-incorporated methylbenzyl-substituted ginkgolide B ([11C]-3). PET studies in monkeys showed low uptake of [18F]-2 into the brain, but small amounts of [11C]-3 were accumulated in the parenchyma. Furthermore, when cyclosporine A was preadministered to rats, the accumulation of [18F]-2 in the rat brain did not significantly change, however, the accumulation of [11C]-3 was five times higher than that in the control rat. These results provide effective approaches for investigating the drug potential of ginkgolides.

A novel method for preparing a diverse range of o-sulfanylanilines is described. Direct thioamination of arynes with sulfilimines gives o-sulfanylanilines, involving C–N and C–S bond formations and migratory N-arylation.

An efficient deborylthiolation of aryl- and alkenylborons with thiosulfonates has been achieved under mild conditions using a copper catalyst. All steps of the experimental process were free from unpleasant odors. The mild reaction conditions as well as ready availability of boron compounds and thiosulfonates enabled easy access to an array of sulfides, including those bearing sensitive functional groups.

Cycloheptynes and cyclooctynes were efficiently generated via a sulfoxide–magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates. Cycloadditions between various ynophiles and the cycloalkynes generated by this method proceeded efficiently, providing an easy method to prepare a wide range of heterocycles fused with seven- or eight-membered carbocycles.

A novel synthetic method for v-coelenterazine (v-CTZ), which is a vinylene-bridged analog of native CTZ with a large red-shifted luminescence property, is described. The synthesis was achieved in a concise way through the use of three sequential cross-coupling reactions and ring-closing metathesis (RCM). A newly synthesized C2-modified trifluoromethyl analog cf3-v-CTZ showed slightly more red-shifted luminescence than v-CTZ when it was used as a substrate for Renilla luciferases.

A transient protection method of cyclooctynes from a click reaction with an azide through 1:1 complexation with a cationic copper(I) salt is reported. The application of the method to a cyclooctyne bearing a terminal alkyne enabled the selective copper-catalyzed click conjugation with an azide at the terminal alkyne moiety, which made cyclooctyne derivatives readily accessible.

3-Triflyloxybenzyne was generated via an iodine–magnesium exchange reaction of 1,3-bis(triflyloxy)-2-iodobenzene using the trimethylsilylmethyl Grignard reagent. Various arynophiles and nucleophiles reacted regioselectively with 3-triflyoxybenzyne to afford cycloadducts and unique aryl triflones, which were provided via thia-Fries rearrangement.

An efficient synthetic method for versatile dibenzoxaborins based on boron-selective Suzuki–Miyaura cross-coupling between o-borylphenols and aryl halides or triflates bearing a 1,8-diaminonaphthalene-protected o-boryl group is reported. A short synthesis of defucogilvocarcin M was achieved using the proposed method in combination with several other boron-mediated transformations.

A modular synthetic method for bis- and tris-1,2,3-triazoles that include a benzotriazole structure was developed on the basis of sequential azide–aryne and azide–alkyne cycloadditions. The key to success was efficient halogen–metal exchange reaction-mediated generation of aryne from ortho-iodoaryl triflates bearing a base-sensitive terminal alkyne moiety, which was achieved using trimethylsilylmethyl Grignard reagent.

An efficient method of generating aryne has been achieved by treating ortho-(trifluoromethanesulfonyloxy)arylboronic acid pinacol ester with tert- or sec-butyllithium. Monitoring the reaction by 11B NMR has indicated that a boron-ate complex formed in situ is the eventual precursor that converts into aryne near room temperature. The prior formation of the ate complex at a low temperature has enabled us to use various arynophiles, including those bearing base-sensitive groups. The ready availability of the aryne precursors and mutual orthogonality in aryne generation with widely used ortho-silylaryl triflate have enhanced the utility of the method.

A practical method to prepare precursor of [N-methyl-11C]vorozole ([11C]vorozole), an efficient positron emission tomography (PET) tracer for imaging aromatase in the living body, was established. Sufficient amount of the racemate including norvorozole, a demethylated vorozole derivative used as a precursor of [11C]vorozole, became available by means of high-yield eight-step synthesis. The enantiomers were separated by preparative HPLC using a chiral stationary phase column to give optically pure norvorozole and its enantiomer. From the latter, ent-[11C]vorozole, an enantiomer of [11C]vorozole, was prepared and used in the PET study for the first time, which was shown to bind very weakly to aromatase in rhesus monkey brain supporting the previous pharmacological results. The stable supply of norvorozole will facilitate further researches on aromatase in the living body including brain by the PET technique.

The strain-promoted “double-click” (SPDC) reaction using Sondheimer diyne, a novel convergent method conjugating three molecules spontaneously, has enabled us to readily modify an azido-biomolecule with a small reporter azido-molecule.

Aequorin is a Ca2+-binding photoprotein and consists of an apoprotein (apoaequorin) and a 2-peroxide of coelenterazine. Eight new coelenterazine analogues modified at the C2-position were synthesized and incorporated into recombinant apoaequorin with O2 to yield different semisynthetic aequorins. The luminescence properties and the sensitivity to Ca2+ of these semisynthetic aequorins were characterized. Two semisynthetic aequorins, namely me- and cf3-aequorin, showed a slow decay of the luminescence pattern with less sensitivity to Ca2+ and were useful for the cell-based G-protein-coupled receptor (GPCR) reporter assays.

The cold-induced expression system in Escherichia coli is useful and we have applied this system to prepare the coelenterazine-utilizing luciferases including Renilla luciferase (RLase), a red-shifted variant of Renilla luciferase (RLase-547), the catalytic domain of Oplophorus luciferase (19kOLase) and Gaussia luciferase (GLase). The luminescence properties of the purified luciferases were characterized by using 10 kinds of C2-modified coelenterazine analogues as a substrate. The order of the maximal luminescence intensity for native coelenterazine was GLase (100%) > RLase (8.0%) > RLase-547 (0.73%) > 19kOLase (0.09%) under our assay conditions. The substrate specificities of coelenterazine-utilizing luciferases for the C2-modified analogues showed significant differences, but the emission peaks catalyzed by coelenterazine-utilizing luciferases were not affected by the C2-substituted coelenterazine. These results suggest that the catalytic environment for the oxygenation process of coelenterazine and the excited species of coelenteramide might be different among coelenterazine-utilizing luciferases.Highlights► The coelenterazine-utilizing luciferases show different luminescence characteristics. ► The C2-modified coelenterazine analogues are used for the luciferase reaction. ► The emission peaks are not affected by the C2-substituted coelenterazines. ► Gaussia luciferase has the highest luminescence activity among luciferases. ► The catalytic domain of Oplophorus luciferase shows broad substrate specificity.

An efficient deborylthiolation of aryl- and alkenylborons with thiosulfonates has been achieved under mild conditions using a copper catalyst. All steps of the experimental process were free from unpleasant odors. The mild reaction conditions as well as ready availability of boron compounds and thiosulfonates enabled easy access to an array of sulfides, including those bearing sensitive functional groups.

A modular synthetic method for bis- and tris-1,2,3-triazoles that include a benzotriazole structure was developed on the basis of sequential azide–aryne and azide–alkyne cycloadditions. The key to success was efficient halogen–metal exchange reaction-mediated generation of aryne from ortho-iodoaryl triflates bearing a base-sensitive terminal alkyne moiety, which was achieved using trimethylsilylmethyl Grignard reagent.

The strain-promoted “double-click” (SPDC) reaction using Sondheimer diyne, a novel convergent method conjugating three molecules spontaneously, has enabled us to readily modify an azido-biomolecule with a small reporter azido-molecule.

Thiazolobenzyne, which is a benzyne species fused with a thiazole ring, was efficiently generated via an iodine–magnesium exchange reaction of an ortho-iodoaryl triflate-type precursor using a trimethylsilylmethyl Grignard reagent as an activator. A wide range of arynophiles reacted efficiently with the thiazolobenzynes generated by this method to afford various multisubstituted benzothiazoles.

3-Triflyloxybenzyne was generated via an iodine–magnesium exchange reaction of 1,3-bis(triflyloxy)-2-iodobenzene using the trimethylsilylmethyl Grignard reagent. Various arynophiles and nucleophiles reacted regioselectively with 3-triflyoxybenzyne to afford cycloadducts and unique aryl triflones, which were provided via thia-Fries rearrangement.

Cycloheptynes and cyclooctynes were efficiently generated via a sulfoxide–magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates. Cycloadditions between various ynophiles and the cycloalkynes generated by this method proceeded efficiently, providing an easy method to prepare a wide range of heterocycles fused with seven- or eight-membered carbocycles.