Mitsuhiro Arisawa

Efficient oxidative biaryl coupling reaction of phenol ether derivatives using hypervalent iodine(III) reagents

Abstract Oxidative biaryl coupling reaction of phenol ether derivatives with the hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA), in the presence of BF3·Et2O gave a variety of substituted biphenyl and binaphthyl compounds in high yields. Replacement of PIFA with a more practical polymer-supported hypervalent iodine reagent has also been achieved.

Synthesis of substituted 1,2-dihydroquinolines and quinolines using ene–ene metathesis and ene–enol ether metathesis

Abstract We describe a novel and convenient method for quinoline synthesis using ring-closing olefin metathesis (RCM), ene–ene metathesis, and ene–enol ether metathesis. We also report the first example of enol silyl ether–ene metathesis to produce cyclic enol silyl ether. Using this method, versatile substituted quinoline derivatives were readily prepared in excellent yield from anthranilic acid derivatives.

Sulfur Modification of Au via Treatment with Piranha Solution Provides Low-Pd Releasing and Recyclable Pd Material, SAPd

We have found in the SR-HXPS measurement of Piranha-treated Au(111)/mica that the gold surface underwent sulfur modification during this treatment, which was believed to have only removed impurities from the gold surface. We also successfully developed a practical Pd material, SAPd, whose Pd was immobilized on sulfur-modified Au. With the lowest Pd-releasing levels and high recyclability, this is one of the best Pd materials thus far developed. Because it leaches extremely low levels of Pd into reaction mixtures, removal of the residual Pd is unnecessary using SAPd, even in syntheses involving pharmaceutical ingredients.

Palladium-Catalyzed Arylation of Cyclopropanes via Directing Group-Mediated C(sp3)–H Bond Activation To Construct Quaternary Carbon Centers: Synthesis of cis- and trans-1,1,2-Trisubstituted Chiral Cyclopropanes

Pd(II)-catalyzed tertiary C(sp(3))-H arylation of cyclopropanes via directing group-mediated C-H activation for the construction of a chiral quaternary carbon center on cyclopropanes using aryl iodides as a coupling partner is reported. The arylation had a wide substrate scope and good functional group tolerance, including heteroaryl iodides, to provide various chiral arylcyclopropanes with the cis- and trans-1,1,2-trisubstituted structures.

Conformational Restriction Approach to β-Secretase (BACE1) Inhibitors: Effect of a Cyclopropane Ring To Induce an Alternative Binding Mode

Improvement of a drugs binding activity using the conformational restriction approach with sp³ hybridized carbon is becoming a key strategy in drug discovery. We applied this approach to BACE1 inhibitors and designed four stereoisomeric cyclopropane compounds in which the ethylene linker of a known amidine-type inhibitor 2 was replaced with chiral cyclopropane rings. The synthesis and biologic evaluation of these compounds revealed that the cis-(1S,2R) isomer 6 exhibited the most potent BACE1 inhibitory activity among them. X-ray structure analysis of the complex of 6 and BACE1 revealed that its unique binding mode is due to the apparent CH-π interaction between the rigid cyclopropane ring and the Tyr71 side chain. A derivatization study using 6 as a lead molecule led to the development of highly potent inhibitors in which the structure-activity relationship as well as the binding mode of the compounds clearly differ from those of known amidine-type inhibitors.

Potent Proteasome Inhibitors Derived from the Unnatural cis-Cyclopropane Isomer of Belactosin A: Synthesis, Biological Activity, and Mode of Action

The natural product belactosin A (1) with a trans-cyclopropane structure is a useful prototype compound for developing potent proteasome (core particle, CP) inhibitors. To date, 1 and its analogues are the only CP ligands that bind to both the nonprimed S1 pocket as well as the primed substrate binding channel; however, these molecules harbor a high IC50 value of more than 1 μM. We have performed structure-activity relationship studies, thereby elucidating unnatural cis-cyclopropane derivatives of 1 that exhibit high potency to primarily block the chymotrypsin-like active site of the human constitutive (cCP) and immunoproteasome (iCP). The most active compound 3e reversibly inhibits cCP and iCP similarly with an IC50 of 5.7 nM. X-ray crystallographic analysis of the yeast proteasome in complex with 3e revealed that the ligand is accommodated predominantly into the primed substrate binding channel and covalently binds to the active site threonine residue via its β-lactone ring-opening.

Palladium-Nanoparticle-Catalyzed 1,7-Palladium Migration Involving C–H Activation, Followed by Intramolecular Amination: Regioselective Synthesis of N1-Arylbenzotriazoles and an Evaluation of Their Inhibitory Activity toward Indoleamine 2,3-Dioxygenase

A sulfur-modified gold-supported palladium material (SAPd) has been developed bearing palladium nanoparticles on its surface. Herein, we report for the first time the use of SAPd to affect a Pd-nanoparticle-catalyzed 1,7-Pd migration reaction for the synthesis of benzotriazoles via C-H bond activation. The resulting benzotriazoles were evaluated in terms of their inhibitory activity toward indoleamine 2,3-dioxygenase.

DJ-1 cooperates with PYCR1 in cell protection against oxidative stress.

DJ-1, a product of the DJ-1/PARK7 gene, has been suggested to play various functions involved in transcriptional regulation, protease activity, anti-oxidative stress activity, and regulation of mitochondrial complex I. Such a variety of functions of DJ-1 are supposed to be realized through interactions with different partner proteins. Among the candidates for DJ-1-partner proteins detected in TOF-MAS analyses of the cellular proteins co-immunoprecipitated with DJ-1, we focused here pyrroline-5-carboxylate reductase 1, PYCR1, a final key enzyme for proline biosynthesis. DJ-1 directly bound to PYCR1 in vivo and in vitro. DJ-1 and PYCR1 colocalized in mitochondria, and both were suggested to be involved in regulation of mitochondrial membrane potential, but differently. DJ-1 enhanced the enzymatic activity of PYCR1 in vitro. The cells knocked down for DJ-1 and PYCR1 showed lower viability under oxidative stress conditions. No additive nor synergistic results were obtained for the cells that had been knocked down for both DJ-1 and PYCR1, suggesting that DJ-1 and PYCR1 are on the same pathway of anti-oxidative stress protection of the cells.

Synthesis of 2,3- and 3,4-methanoamino acid equivalents with stereochemical diversity and their conversion into the tripeptide proteasome inhibitor belactosin a and its highly potent cis-cyclopropane stereoisomer.

A series of chiral 2,3- and 3,4-methanoamino acid equivalents of stereochemical diversity were designed and synthesized from our chiral cyclopropane units, using a diastereoselective Grignard addition with ( R)- or ( S)- t-butanesulfinyl imines as the key step. These equivalents were converted into the proteasome inhibitor belactosin A and its cis-cyclopropane stereoisomer. The unnatural cis-isomer was shown to be more than twice as potent as belactosin A as a proteasome inhibitor.

Suzuki–Miyaura cross-coupling reactions using a low-leaching and highly recyclable gold-supported palladium material and two types of microwave equipments

We designed Suzuki–Miyaura cross-coupling reactions in conjunction with sulfur-modified Au-supported Pd material (SAPd) and two types of microwaves, single-mode and multi-mode. The entire microwave-facilitated process provided advantages over conventional heating in that reactivity of the less reactive arylbromides was induced and the reaction time was reduced.