Satoshi Shuto

Synthesis and characterization of a series of highly fluorogenic substrates for glutathione transferases, a general strategy.

Glutathione transferases (GSTs) are used in biotechnology applications as fusion partners for facile purification and are also overexpressed in certain tumors. Consequently, there is a need for sensitive detection of the enzymes. Here we describe a general strategy for the synthesis and characterization of novel fluorogenic substrates for GSTs. The substrates were synthesized by introducing an electrophilic sulfonamide linkage to fluorescent molecules containing an amino group [e.g., 2,4-dinitrobenzenesulfonamide (DNs) derivatives of coumarin, cresyl violet, and rhodamine]. The derivatives were essentially nonfluorescent, and upon GST catalyzed cleavage of the dinitrobenzenesulfonamide, free fluorophore is released (and 1-glutathionyl-2,4-dinitrobenzene + SO(2)). All the coumarin-, cresyl violet- and rhodamine-based fluorogenic probes turned out to be good substrates for most GSTs, especially for GSTA(1-1), in terms of strong fluorescence increases (71-1200-fold), high k(cat)/K(m) values (10(4)-10(7) M(-1) s(-1)) and significant rate enhancements (10(6)-10(9)-fold). The substrates were successfully applied to quantitate very low levels of GST activity in cell extracts and DNs-cresyl violet was also successfully applied to the imaging of microsomal MGST(1) activity in living cells. The cresyl violet stained cells retained their fluorescence after fixation, which is a very useful property. In summary, we describe a general and versatile strategy to generate fluorogenic GST substrates, some of them providing the most sensitive assays so far described for GSTs.

Rolling Circle Translation of Circular RNA in Living Human Cells.

We recently reported that circular RNA is efficiently translated by a rolling circle amplification (RCA) mechanism in a cell-free Escherichia coli translation system. Recent studies have shown that circular RNAs composed of exonic sequences are abundant in human cells. However, whether these circular RNAs can be translated into proteins within cells remains unclear. In this study, we prepared circular RNAs with an infinite open reading frame and tested their translation in eukaryotic systems. Circular RNAs were translated into long proteins in rabbit reticulocyte lysate in the absence of any particular element for internal ribosome entry, a poly-A tail, or a cap structure. The translation systems in eukaryote can accept much simpler RNA as a template for protein synthesis by cyclisation. Here, we demonstrated that the circular RNA is efficiently translated in living human cells to produce abundant protein product by RCA mechanism. These findings suggest that translation of exonic circular RNAs present in human cells is more probable than previously thought.

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.

Structure Formation and Catalytic Activity of DNA Dissolved in Organic Solvents

Equal-opportunity dissolver: By attaching polyethylene glycol at its 5 end, DNA (PEG-DNA) can be solubilized in various organic solvents and was shown to form G-quadruplexes by CD spectroscopy. A complex containing iron(III) protoporphyrinu2005IX (hemin) and G-quadruplex-forming PEG-DNA catalyzed an oxidative reaction in methanol (see scheme).

Determination of ω-6 and ω-3 PUFA metabolites in human urine samples using UPLC/MS/MS.

The ω-6 and ω-3 polyunsaturated fatty acids (PUFAs) such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are the precursors of various bioactive lipid mediators including prostaglandins, thromboxanes, leukotrienes, hydroxyeicosatetraenoic acid, isoprostanes, lipoxins, and resolvins (Rvs). These lipid mediators play important roles in various physiological and pathological processes. The quantitative determination of PUFA metabolites seems necessary for disease research and for developing biomarkers. However, there is a paucity of analytical methods for the quantification of ω-6 and ω-3 PUFA metabolites—the specialized pro-resolving mediators (SPMs) present in the human urine. We developed a method for the quantification of ω-6 and ω-3 PUFA metabolites present in human urine using ultra-performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS). The developed method shows good linearity, with a correlation coefficient >0.99 for all of the analytes. The validation results indicate that our method is adequately reliable, accurate, and precise. The method was successfully used to examine urine samples obtained from 43 healthy volunteers. We could identify 20 PUFA metabolites, and this is the first report of the quantitative determination of RvD1, 17(R)-RvD1, 11-dehydro thromboxane B3, RvE2, and 5(S)-HETE in human urine. The urinary 8-iso PGF2α and PGE2 levels were significantly higher in the men smokers than in the men nonsmokers (pu2009<u20090.05). In this study, we developed an accurate, precise, and novel analytical method for estimating the ω-6 and ω-3 PUFA metabolites, and this is the first report that the SPMs derived from EPA and DHA are present in human urine.

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.

1,2,3-Triazole-Containing Uracil Derivatives with Excellent Pharmacokinetics as a Novel Class of Potent Human Deoxyuridine Triphosphatase Inhibitors

Deoxyuridine triphosphatase (dUTPase) has emerged as a potential target for drug development as a 5-fluorouracil-based combination chemotherapy. We describe the design and synthesis of a novel class of human dUTPase inhibitors, 1,2,3-triazole-containing uracil derivatives. Compound 45a, which possesses 1,5-disubstituted 1,2,3-triazole moiety that mimics the amide bond of tert-amide-containing inhibitor 6b locked in a cis conformation showed potent inhibitory activity, and its structure-activity relationship studies led us to the discovery of highly potent inhibitors 48c and 50c (IC(50) = ~0.029 μM). These derivatives dramatically enhanced the growth inhibition activity of 5-fluoro-2-deoxyuridine against HeLa S3 cells in vitro (EC(50) = ~0.05 μM). In addition, compound 50c exhibited a markedly improved pharmacokinetic profile as a result of the introduction of a benzylic hydroxy group and significantly enhanced the antitumor activity of 5-fluorouracil against human breast cancer MX-1 xenograft model in mice. These data indicate that 50c is a promising candidate for combination cancer chemotherapies with TS inhibitors.

Investigation of the Bioactive Conformation of Histamine H3 Receptor Antagonists by the Cyclopropylic Strain-Based Conformational Restriction Strategy

We previously identified the highly potent histamine H(3) receptor antagonists (1R,2S)-2-[2-(4-chlorobenzylamino)ethyl]-1-(1H-imidazol-4-yl)cyclopropane (1) and its enantiomer ent-1. Although the conformations of 1 and ent-1 are restricted by the central cyclopropane ring, the 2-(4-chlorobenzylamino)ethyl side chain essential for the H(3) receptor binding may somewhat freely rotate. To investigate the bioactive conformation, the 1-ethyl-substituted derivatives 2a and 2b and their enantiomers ent-2a and ent-2b were designed as side chain conformation-restricted analogues of 1 and ent-1, based on the cyclopropylic strain. These compounds were synthesized, and their analysis by NMR and calculations suggested that the side chain moiety was effectively restricted in a syn-form or an anti-form by the cyclopropylic strain as expected. Pharmacological evaluation and docking simulation showed that the bioactive conformations of 1 and ent-1 appear to be the syn-form and the anti-form, respectively. Thus, the cyclopropylic strain can be effectively used for conformational restriction of the side chain moiety of cyclopropane compounds.