Naoki Kanoh

The identification of an osteoclastogenesis inhibitor through the inhibition of glyoxalase I

Osteoclasts, bone-resorptive multinucleated cells derived from hematopoietic stem cells, are associated with many bone-related diseases, such as osteoporosis. Osteoclast-targeting small-molecule inhibitors are valuable tools for studying osteoclast biology and for developing antiresorptive agents. Here, we have discovered that methyl-gerfelin (M-GFN), the methyl ester of the natural product gerfelin, suppresses osteoclastogenesis. By using M-GFN-immobilized beads, glyoxalase I (GLO1) was identified as an M-GFN-binding protein. GLO1 knockdown and treatment with an established GLO1 inhibitor in osteoclast progenitor cells interfered with osteoclast generation, suggesting that GLO1 activity is required for osteoclastogenesis. In cells, GLO1 plays a critical role in the detoxification of 2-oxoaldehydes, such as methylglyoxal. M-GFN inhibited the enzymatic activity of GLO1 in vitro and in situ. Furthermore, the cocrystal structure of the GLO1/M-GFN complex revealed the binding mode of M-GFN at the active site of GLO1. These results suggest that M-GFN targets GLO1, resulting in the inhibition of osteoclastogenesis.

Highly enantioselective intramolecular aza-spiroannulation onto indoles using chiral rhodium catalysis: asymmetric entry to the spiro-β-lactam core of chartellines

A versatile, highly enantiocontrolled entry to the spiro-beta-lactam core of chartellines has been developed by expanding the scope of oxidative nitrogen atom transfer methodology based on chiral Rh-nitrenoid species.

Synthetic Studies on Daphnicyclidin A: Enantiocontrolled Construction of the BCD Ring System

An enantiocontrolled entry to the tricyclic core of daphnicyclidin A with five chiral centers including an all-carbon quaternary center is reported. The synthesis features a highly diastereoselective conjugate addition of nitromethane, an Ireland-Claisen rearrangement, and a tandem acyliminium/Mannich-type reaction.

Structure-activity relationship of C5-curcuminoids and synthesis of their molecular probes thereof.

A series of novel analogues of 1,5-bis(4-hydroxy-3-methoxyphenyl)-penta-(1E,4E)-1,4-dien-3-one (C(5)-curcumin), which is a natural analogue of curcumin isolated from the rhizomes of Curcuma domestica Val. (Zingiberacea), were synthesized and evaluated for their cytotoxicities against human colon cancer cell line HCT-116 to conclude the SAR of C(5)-curcuminoids for further development of their use in cancer chemotherapy: (1) Bis(arylmethylidene)acetone serves as a promising skeleton for eliciting cytotoxicity. (2) The 3-oxo-1,4-pentadiene structure is essential for eliciting cytotoxicity. (3) As for the extent of the aromatic substituents, hexasubstituted compounds exhibit strong activities, in which 3,4,5-hexasubstitution results in the highest potency. (5) The symmetry between two aryl rings is not an essential requirement for bis(arylmethylidene)acetones to elicit cytotoxicity. (6) para-Positions allows the installation of additional functional groups for use as molecular probes. By taking advantage of the SAR diagram, we have elaborated several advanced derivatives having GI(50) of single-digit micromolar potencies that will function as molecular probes to target and/or report key biomolecules interacting with curcumin and C(5)-curcumin.

Syntheses and biological evaluation of irciniastatin A and the C1-C2 alkyne analogue.

Syntheses of both natural (+)- and unnatural (-)-irciniastatin A (aka psymberin) as well as a C1-C2 alkyne analogue of (+)-irciniastatin A have been achieved. The key features of the syntheses include a highly regioselective epoxide-opening reaction and a late-stage assembly of C1-C6, C8-C16, and C17-C25 fragments. (+)-Alkymberin retained a high level of cytotoxicity, whereas (-)-irciniastatin A showed almost no activity. These results suggest that (+)-alkymberin could be a useful enantio-differential probe for mode-of-action study.

An expedient route to a potent gastrin/CCK-B receptor antagonist (+)-AG-041R.

An enantiocontrolled synthesis of (+)-AG-041R (1), a potent gastrin/CCK-B receptor antagonist, has been achieved employing a chiral rhodium(II)-catalyzed, oxidative intramolecular aza-spiroannulation as the key step.

Phoslactomycin targets cysteine‐269 of the protein phosphatase 2A catalytic subunit in cells

According to the chemical genetic approach, small molecules that bind directly to proteins are used to analyze protein function, thereby enabling the elucidation of complex mechanisms in mammal cells. Thus, it is very important to identify the molecular targets of compounds that induce a unique phenotype in a target cell. Phoslactomycin A (PLMA) is known to be a potent inhibitor of protein Ser/Thr phosphatase 2A (PP2A); however, the inhibitory mechanism of PP2A by PLMA has not yet been elucidated. Here, we demonstrated that PLMA directly binds to the PP2A catalytic subunit (PP2Ac) in cells by using biotinylated PLMA, and the PLMA‐binding site was identified as the Cys‐269 residue of PP2Ac. Moreover, we revealed that the Cys‐269 contributes to the potent inhibition of PP2Ac activity by PLMA. These results suggest that PLMA is a PP2A‐selective inhibitor and is therefore expected to be useful for future investigation of PP2A function in cells.

Total synthesis of methyl sarcophytoate, a marine natural biscembranoid.

The total synthesis of methyl sarcophytoate (1), a marine natural biscembranoid, has been achieved by the thermal Diels-Alder reaction between the 14-membered dienophile unit, methyl sarcoate (2), and the 14-membered diene unit 64. Methyl sarcoate (2) was prepared using n-BuLi-Bu(2)Mg-mediated dithiane coupling, Kosugi-Migita-Stille coupling, and Grubbs ring-closing metathesis. The diene unit 64 was prepared using Sharpless asymmetric epoxidation, Grubbs ring-closing metathesis, 6-exo-tet epoxide opening, and n-BuLi-Bu(2)Mg-mediated Ito-Kodama cyclization. The final Diels-Alder reaction between 2 and 64 proceeded with high site, endo/exo, pi-face, and regioselectivities. During this reaction, partial E --> Z isomerization at the C4 position was observed.

Asymmetric Total Synthesis of (−)-Scabronine G via Intramolecular Double Michael Reaction and Prins Cyclization

The enantioselective total synthesis of (-)-scabronine G is described. The key features of the present synthesis include the construction of a 5-6 ring system containing two quaternary carbon centers via a diastereoselective intramolecular double Michael reaction and the formation of a seven-membered ring using a Prins cyclization.

Irciniastatin A induces JNK activation that is involved in caspase-8-dependent apoptosis via the mitochondrial pathway.

Irciniastatin A (ISA)/psymberin, a pederin-type natural product isolated from marine sponge, exhibits extremely potent and selective cytotoxicity against certain human cancer cell lines, but its molecular target and cytotoxic mechanisms are still unknown. Here we show that ISA is a potent inhibitor of protein translation, and induces apoptosis accompanied with activation of the stress-activated protein kinases via the mitochondrial pathway in human leukemia Jurkat cells. ISA potently inhibited protein translation, and induced a slow but prolonged activation of the stress-activated protein kinases, JNK and p38, at between 1h and 6h after treatment. In Bcl-x(L)-transfected cells, the activation of JNK and p38 by ISA was shortened. The same results were obtained in the cells treated with N-acetyl-L-cysteine, suggesting that the prolonged activation of JNK and p38 by ISA is mediated by reactive oxygen species generated from mitochondria. ISA strongly induced apoptosis, which was partially suppressed by the JNK inhibitor SP600125, but not by the p38 inhibitor SB202190. Apoptosis induction by ISA was partially reduced, but not suppressed by SP600125 in caspase-8-deficient Jurkat cells. These results suggest that ISA activates stress-activated kinases by a mitochondria-mediated mechanism, and that activation of JNK is required for caspase-8-dependent apoptosis.