Shin-ichi Kawaguchi

Highly Selective Hydroiodation of Alkynes Using an Iodine−Hydrophosphine Binary System

A novel hydroiodation of alkynes (1) using an iodine/hydrophosphine binary system takes place regioselectively to provide the corresponding Markovnikov-type adducts (2) in good yield. This hydroiodation is advantageous in terms of mild conditions, convenient operation, and tolerance to various functional groups.

Highly Regioselective Simultaneous Introduction of Phosphino and Seleno Groups into Unsaturated Bonds by the Novel Combination of (Ph2P)2 and (PhSe)2 upon Photoirradiation

A novel combination of tetraphenyldiphosphine and diphenyl diselenide under photoirradiation conditions attains simultaneous introduction of diphenylphosphino and phenylseleno groups into carbon-carbon unsaturated bonds such as terminal alkynes or allenes, regioselectively.

Palladium-Catalyzed Synthesis of α-Diimines from Triarylbismuthines and Isocyanides

In this study, we report a highly selective coupling reaction between triarylbismuthines and isocyanides using palladium diacetate as the catalyst, affording α-diimines, with the formation of three C-C bonds. Among several aryl sources (Ar-YLn: Y = B, Sn, Pb, Sb, Bi, I), only triarylbismuthines successfully undergo coupling with isocyanides to selectively afford α-diimines. The coupling reaction exhibits the advantages of high atom economy and convenient operation, with no need for any additive.

Hypoxia Signaling Cascade for Erythropoietin Production in Hepatocytes

ABSTRACT Erythropoietin (Epo) is produced in the kidney and liver in a hypoxia-inducible manner via the activation of hypoxia-inducible transcription factors (HIFs) to maintain oxygen homeostasis. Accelerating Epo production in hepatocytes is one plausible therapeutic strategy for treating anemia caused by kidney diseases. To elucidate the regulatory mechanisms of hepatic Epo production, we analyzed mouse lines harboring liver-specific deletions of genes encoding HIF-prolyl-hydroxylase isoforms (PHD1, PHD2, and PHD3) that mediate the inactivation of HIF1α and HIF2α under normal oxygen conditions. The loss of all PHD isoforms results in both polycythemia, which is caused by Epo overproduction, and fatty livers. We found that deleting any combination of two PHD isoforms induces polycythemia without steatosis complications, whereas the deletion of a single isoform induces no apparent phenotype. Polycythemia is prevented by the loss of either HIF2α or the hepatocyte-specific Epo gene enhancer (EpoHE). Chromatin analyses show that the histones around EpoHE dissociate from the nucleosome structure after HIF2α activation. HIF2α also induces the expression of HIF3α, which is involved in the attenuation of Epo production. These results demonstrate that the total amount of PHD activity is more important than the specific function of each isoform for hepatic Epo expression regulated by a PHD-HIF2α-EpoHE cascade in vivo.

A Highly Regioselective Palladium-Catalyzed Hydrophosphination of Alkynes Using a Diphosphine−Hydrosilane Binary System

A novel transition-metal-catalyzed hydrophosphination of terminal alkynes using a diphosphine-hydrosilane binary system takes place regioselectively to provide vinylic phosphines, which undergo air oxidation during workup, affording the corresponding vinylphosphine oxides in good yields. In this hydrophosphination, hydrosilanes act as a useful hydrogen source, and furthermore, small amounts of oxygen is required to accomplish the reaction efficiently.

Highly Selective Phosphinylphosphination of Alkenes with Tetraphenyldiphosphine Monoxide.

In sharp contrast to tetraphenyldiphosphine, which does not add to carbon-carbon double bonds efficiently, its monoxide, [Ph2 P(O)PPh2 ] can engage in a radical addition to various alkenes, thus affording the corresponding 1-phosphinyl-2-phosphinoalkanes regioselectively, and they can be converted into their sulfides by treatment with elemental sulfur. The phosphinylphosphination proceeds by the homolytic cleavage of the P(V) (O)-P(III) single bond of Ph2 P(O)PPh2 , followed by selective attack of the phosphinyl radical at the terminal position of the alkenes, and selective trapping of the resulting carbon radical by the phosphino group. Furthermore, the phosphinylphosphination product could be converted directly into its platinum complex with a hemilabile P,Ou2005chelation.

RHODIUM-CATALYZED ANTI-MARKOVNIKOV-TYPE HYDROPHOSPHINATION OF TERMINAL ALKYNES WITH DIPHOSPHINES AND HYDROSILANES IN THE PRESENCE OF OXYGEN

A novel rhodium(I)-catalyzed hydrophosphination of terminal alkynes with diphosphines and hydrosilanes takes place regioselectively in the presence of small amounts of oxygen. After air-oxidation during workups, the corresponding anti-Markovnikov–type vinylic phosphine oxides were obtained in good yields.

Discovery of an NRF1-specific inducer from a large-scale chemical library using a direct NRF1-protein monitoring system.

NRF1 (NF‐E2‐p45‐related factor 1) plays an important role in the regulation of genes encoding proteasome subunits, a cystine transporter, and lipid‐metabolizing enzymes. Global and tissue‐specific disruptions of the Nrf1 gene in mice result in embryonic lethality and spontaneous development of severe tissue defects, respectively, suggesting NRF1 plays a critical role in vivo. Mechanistically, the continuous degradation of the NRF1 protein by the proteasome is regarded as a major regulatory nexus of NRF1 activity. To develop NRF1‐specific inducers that act to overcome the phenotypes related to the lack of NRF1 activity, we constructed a novel NRF1ΔC‐Luc fusion protein reporter and developed cell lines that stably express the reporter in Hepa1c1c7 cells for use in high‐throughput screening. In screening of a chemical library with this reporter system, we identified two hit compounds that significantly induced luciferase activity. Through an examination of a series of derivatives of one of the hit compounds, we identified T1‐20, which induced a 70‐fold increase in luciferase activity. T1‐20 significantly increased the level of NRF1 protein in the mouse liver, indicating that the compound is also functional in vivo. Thus, these results show the successful identification of the first small chemical compounds which specifically and significantly induce NRF1.

Photoinduced synthesis of unsymmetrical diaryl selenides from triarylbismuthines and diaryl diselenides

Summary A novel method of photoinduced synthesis of unsymmetrical diaryl selenides from triarylbismuthines and diaryl diselenides has been developed. Although the arylation reactions with triarylbismuthines are usually catalyzed by transition-metal complexes, the present arylation of diaryl diselenides with triarylbismuthines proceeds upon photoirradiation in the absence of transition-metal catalysts. A variety of unsymmetrical diaryl selenides can be conveniently prepared by using this arylation method.

Hypoxia-Sensitive Reporter System for High-Throughput Screening

The induction of anti-hypoxic stress enzymes and proteins has the potential to be a potent therapeutic strategy to prevent the progression of ischemic heart, kidney or brain diseases. To realize this idea, small chemical compounds, which mimic hypoxic conditions by activating the PHD-HIF-α system, have been developed. However, to date, none of these compounds were identified by monitoring the transcriptional activation of hypoxia-inducible factors (HIFs). Thus, to facilitate the discovery of potent inducers of HIF-α, we have developed an effective high-throughput screening (HTS) system to directly monitor the output of HIF-α transcription. We generated a HIF-α-dependent reporter system that responds to hypoxic stimuli in a concentration- and time-dependent manner. This system was developed through multiple optimization steps, resulting in the generation of a construct that consists of the secretion-type luciferase gene (Metridia luciferase, MLuc) under the transcriptional regulation of an enhancer containing 7 copies of 40-bp hypoxia responsive element (HRE) upstream of a mini-TATA promoter. This construct was stably integrated into the human neuroblastoma cell line, SK-N-BE(2)c, to generate a reporter system, named SKN:HRE-MLuc. To improve this system and to increase its suitability for the HTS platform, we incorporated the next generation luciferase, Nano luciferase (NLuc), whose longer half-life provides us with flexibility for the use of this reporter. We thus generated a stably transformed clone with NLuc, named SKN:HRE-NLuc, and found that it showed significantly improved reporter activity compared to SKN:HRE-MLuc. In this study, we have successfully developed the SKN:HRE-NLuc screening system as an efficient platform for future HTS.