Go Hirai

Ginkgolic Acid Inhibits Protein SUMOylation by Blocking Formation of the E1-SUMO Intermediate

Protein modification by small ubiquitin-related modifier proteins (SUMOs) controls diverse cellular functions. Dysregulation of SUMOylation or deSUMOylation processes has been implicated in the development of cancer and neurodegenerative diseases. However, no small-molecule inhibiting protein SUMOylation has been reported so far. Here, we report inhibition of SUMOylation by ginkgolic acid and its analog, anacardic acid. Ginkgolic acid and anacardic acid inhibit protein SUMOylation both in vitro and in vivo without affecting in vivo ubiquitination. Binding assays with a fluorescently labeled probe showed that ginkgolic acid directly binds E1 and inhibits the formation of the E1-SUMO intermediate. These studies will provide not only a useful tool for investigating the roles of SUMO conjugations in a variety of pathways in cells, but also a basis for the development of drugs targeted against diseases involving aberrant SUMOylation.

Limited Inhibitory Effects of Oseltamivir and Zanamivir on Human Sialidases

ABSTRACT Oseltamivir (Tamiflu) and zanamivir (Relenza), two extensively used clinically effective anti-influenza drugs, are viral sialidase (also known as neuraminidase) inhibitors that prevent the release of progeny virions and thereby limit the spread of infection. Recently mortalities and neuropsychiatric events have been reported with the use of oseltamivir, especially in pediatric cases in Japan, suggesting that these drugs might also inhibit endogenous enzymes involved in sialic acid metabolism, including sialidase, sialyltransferase, and CMP-synthase, in addition to their inhibitory effects on the viral sialidase. The possible inhibition could account for some of the rare side effects of oseltamivir. However, there has been little direct evidence in regard to the sensitivities of animal sialidases to these drugs. Here, we examined whether these inhibitors might indeed affect the activities of human sialidases, which differ in primary structures and enzyme properties but possess tertiary structures similar to those of the viral enzymes. Using recombinant enzymes corresponding to the four human sialidases identified so far, we found that oseltamivir carboxylate scarcely affected the activities of any of the sialidases, even at 1 mM, while zanamivir significantly inhibited the human sialidases NEU3 and NEU2 in the micromolar range (Ki, 3.7 ± 0.48 and 12.9 ± 0.07 μM, respectively), providing a contrast to the low nanomolar concentrations at which these drugs block the activity of the viral sialidases.

Synthesis of CH2-Linked α(2,3)Sialylgalactose Analogue: On the Stereoselectivity of the Key Ireland-Claisen Rearrangement

A CH 2 -linked alpha(2,3)sialylgalactose analogue was efficiently synthesized using an Ireland-Claisen rearrangement, which was developed recently by our group for constructing a CF 2 -sialoside. The reaction conditions of the rearrangement were optimized for alpha-stereoselective formation of the CH 2 -sialoside. On the basis of the observed temperature effects, the origin of the stereoselectivity of the Ireland-Claisen rearrangement is discussed. Moreover, reconstruction of the 2alpha-hydroxyl group on the galactose unit of the rearrangement product was achieved by means of stereoselective dihydroxylation and deoxygenation.

Enantio-face control by molecular sieves in the asymmetric Diels-Alder reaction

Abstract The presence of molecular sieves 4A (MS 4A) significantly influenced enantioselectivity in the Diels–Alder reaction of 2-methoxy-5-methyl-1,4-benzoquinone with 1-acetoxy-1,3-butadiene promoted by chiral TADDOL–Ti complexes. In the absence of MS 4A the ( R )-adduct was formed in 72% ee, and in the presence of MS 4A the ( S )-enantiomer in up to 53% ee. Capture of HCl by MS 4A has been demonstrated to play a critical role.

Development of a Vaccinia H1-Related (VHR) Phosphatase Inhibitor with a Nonacidic Phosphate-Mimicking Core Structure

Cell growth and intracellular signaling pathways are often regulated by protein phosphorylation, which is controlled by a dynamic balance between the enzymatic activities of protein kinases and protein phosphatases (PPases). PPases have been classified by structure and substrate specificity into protein serine/threonine phosphatases and protein tyrosine phosphatases (PTPs). Dual-specificity protein phosphatases (DSPs) are a PTP subclass that uniquely hydrolyzes the phosphate ester on both a tyrosine residue and either a serine or threonine residue located in the same protein. Vaccinia H1-related phosphatase, VHR, is a member of the DSP family, and dephosphorylates extracellular signal-regulated kinases ERK1/2 and c-Jun Nterminal kinases JNK1/2, which belong to the mitogen-activated protein (MAP) kinase family. In 2006, it was reported that cell-cycle progression in cells lacking VHR was blocked at the G1/S and G2/M transitions. Moreover, since it was recently found that VHR is upregulated in cervical cancer cells, such as HeLa cells, and in prostate cancers, inhibitors of VHR would be not only valuable tools for further biological research, but also candidates as lead compounds for pharmaceutical agents. However, the design of selective inhibitors of individual DSPs is a demanding task because of structural similarities in the active site residues of DSPs. A focused library approach, where a series of derivatives with a phosphate-mimicking core structure are screened for inhibitory activity towards the target phosphatase, can be quite effective for the identification of selective inhibitors of biologically important DSPs. We have previously reported the development of potent DSP inhibitors based on a tetronic acid library derived from the natural product RK-682 (1), in which the 3-acyltetronate anion acts as a phosphate-mimicking core structure. Various other inhibitors of DSPs have been reported in the literature, and many VHR inhibitors contain an acidic functional group, such as a phosphonate, as a phosphate mimic. 11] However, poor cell permeability and enzyme selectivity can often be a problem in this class of inhibitors, which have an acidic character. In fact, 1 was found to be far less potent in cells and to inhibit not only DSPs/PTPs, but also unrelated enzymes such as heparanase and phospholipase A2. [13] Therefore, it is desirable to develop a superior core structure for libraries focused on DSP inhibitors. Herein, we report the design of a new cell-permeable scaffold, RK-682 enamine (RE), for the development of DSP-selective inhibitors and a selective VHR inhibitor. The presence of a negative charge stabilized by delocalization over the three oxygen atoms of 3-acyltetronate is unfavorable for penetration of RK-682 derivatives through the cell membrane. In addition to the acidic nature of the core structure, the long hydrophobic alkyl chain causes RK-682 derivatives to have a detergent-like property, which might result in nonspecific interaction with unrelated enzymes (Figure 1 a).

Convergent synthesis of the ABC-ring moiety of zoanthenol: Intramolecular Mizoroki-Heck reaction

Abstract The highly congested ABC-ring moiety of zoanthenol was stereoselectively synthesized via an alkoxylithium-mediated coupling between the A-ring and C-ring moieties followed by a Mizoroki–Heck-type ring closure.

Synthesis of the DFGH ring system of Type B Physalins: Highly Oxygenated, Cage-Shaped Molecules†

Let the dominos fall: Synthesis of the complex DFGH ring system of the title compounds has been accomplished. The approach features simple treatment of the key intermediate with a Brønsted base to afford the tetracyclic cage-shaped target in one pot through a four-step domino transformation (see scheme; Mc = monochloromesylate, MOM = methoxymethyl).

Development of bis-unsaturated ester aldehydes as amino-glue probes: sequential double azaelectrocyclization as a promising strategy for bioconjugation

The unsaturated ester aldehyde, (E)-3-alkoxycarbonyl-5-phenyl-2,4-dienal, was efficiently dimerized by applying the strain-promoted double-click reaction with sym-dibenzo-1,5-cyclooctadiene-3,7-diyne. The resulting dimerized probe was sequentially reacted first with one peptide molecule and then with a protein or the amino groups on the surface of a live cell through double azaelectrocyclization to achieve highly efficient bioconjugation.

Unexpected Diels-Alder/carbonyl-ene cascade toward the biomimetic synthesis of chloropupukeananin.

The biomimetic synthesis of the advanced model compound of chloropupukeananin has been achieved. The present synthesis features an unexpected enantiomer-differentiating Diels-Alder/carbonyl-ene cascade under high-pressure conditions and a base-promoted migration of the salicyl group.

Rational Design and Synthesis of [5]Helicene-Derived Phosphine Ligands and Their Application in Pd-Catalyzed Asymmetric Reactions

A series of novel optically active [5]helicene-derived phosphine ligands (L1, with a 7,8-dihydro[5]helicene core structure- and L2, with a fully aromatic [5]helicene core structure) were synthesized. Despite their structural similarities, L1 and L2 exhibit particularly different characteristics in their use as chiral ligands. L1 was highly effective in the asymmetric allylation of indoles with 1,3-diphenylallyl acetate (up to 99% ee), and in the etherification of alcohols (up to 96% ee). In contrast, L2 was highly effective in the stereocontrol of helical chirality in Suzuki–Miyaura coupling (SMC) reaction (up to 99% ee). Density functional theory analysis was employed to propose a model that accounts for the origin of the enantioselectivity in these reactions.