Haruhiko Fuwa

C-terminal Fragment of Presenilin Is the Molecular Target of a Dipeptidic γ-Secretase-specific Inhibitor DAPT (N-[N-(3,5-Difluorophenacetyl)-L-alanyl]-S-phenylglycine t-Butyl Ester)

γ-Secretase is a multimeric membrane protein complex composed of presenilin (PS), nicastrin, Aph-1 and, Pen-2 that is responsible for the intramembrane proteolysis of various type I transmembrane proteins, including amyloid β-precursor protein and Notch. The direct labeling of PS polypeptides by transition-state analogue γ-secretase inhibitors suggested that PS represents the catalytic center of γ-secretase. Here we show that one of the major γ-secretase inhibitors of dipeptidic type, N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT), targets the C-terminal fragment of PS, especially the transmembrane domain 7 or more C-terminal region, by designing and synthesizing DAP-BpB (N-[N-(3,5-difluorophenacetyl)-l-alanyl]-(S)-phenylglycine-4-(4-(8-biotinamido)octylamino)benzoyl)benzyl)methylamide), a photoactivable DAPT derivative. We also found that DAP-BpB selectively binds to the high molecular weight γ-secretase complex in an activity-dependent manner. Photolabeling of PS by DAP-BpB is completely blocked by DAPT or its structural relatives (e.g. Compound E) as well as by arylsulfonamides. In contrast, transition-state analogue inhibitor L-685,458 or α-helical peptidic inhibitor attenuated the photolabeling of PS1 only at higher concentrations. These data illustrate the DAPT binding site as a novel functional domain within the PS C-terminal fragment that is distinct from the catalytic site or the substrate binding site.

Suppression of colon cancer metastasis by Aes through inhibition of Notch signaling

Metastasis is responsible for most cancer deaths. Here, we show that Aes (or Grg5) gene functions as an endogenous metastasis suppressor. Expression of Aes was decreased in liver metastases compared with primary colon tumors in both mice and humans. Aes inhibited Notch signaling by converting active Rbpj transcription complexes into repression complexes on insoluble nuclear matrix. In tumor cells, Notch signaling was triggered by ligands on adjoining blood vessels, and stimulated transendothelial migration. Genetic depletion of Aes in Apc(Δ716) intestinal polyposis mice caused marked tumor invasion and intravasation that were suppressed by Notch signaling inhibition. These results suggest that inhibition of Notch signaling can be a promising strategy for prevention and treatment of colon cancer metastasis.

New strategy for convergent synthesis of trans-fused polyether frameworks based on palladium-catalyzed suzuki cross-coupling reaction

Abstract A new strategy for convergent synthesis of trans -fused polyethers based on palladium(0)-catalyzed Suzuki cross-coupling reaction of alkylboranes with cyclic enol triflates has been developed. The present method allows to construct polyether frameworks rapidly and efficiently.

Total Synthesis of (+)‐Neopeltolide

Neopeltolide is a marine macrolide that was isolated from a deep-sea sponge of the Neopeltidae family by Wright and coworkers (Scheme 1). The gross structure, including the relative stereochemistry, was determined based on extensive 2D-NMR analysis. Recently, two independent total syntheses of this natural product, from the research groups of Panek and Scheidt, have resulted in the stereochemical reassignment of the originally proposed structure 1 and the unambiguous determination of the absolute stereostructure, as represented by structure 2 (Scheme 1). Two additional reports on

Synthetic studies on a marine polyether toxin, gambierol: stereoselective synthesis of the EFGH ring system via B-alkyl Suzuki coupling

Abstract A synthetic route to the EFGH ring system ( 3 ) of gambierol ( 1 ), a marine polyether toxin isolated from the dinoflagellate Gambierdiscus toxicus , has been developed. The present synthesis features convergent coupling of the F and H rings followed by ring-closure of the G ring based on the B -alkyl Suzuki reaction of lactone-derived enol phosphates. An angular methyl group at C23 was stereoselectively introduced by treatment of sulfone 32 with trimethylaluminum. Installation of a tertiary alcohol at C21 was accomplished through stereoselcetive dihydroxylation of exo -methylene 36 followed by selective formation of the primary p -toluensulfonate and treatment of the resultant monotosylate 40 with lithium aluminum hydride. Finally, formation of the E ring as a lactone form completed the synthesis of 3 .

A unified total synthesis of aspergillides A and B.

An enantioselective total synthesis of aspergillides A and B has been accomplished based on a unified strategy, wherein a hydroxy-directed, highly chemoselective olefin cross-metathesis and a diastereoselective intramolecular oxa-conjugate cyclization were employed to forge the 2,6-substituted tetrahydropyran substructure.

A general strategy for the convergent synthesis of fused polycyclic ethers via B-alkyl Suzuki coupling: synthesis of the ABCD ring fragment of ciguatoxins

Abstract A new method for convergent coupling of fused polycyclic ethers has been developed, which relies on B -alkyl Suzuki cross-coupling of lactone-derived enol triflates or phosphates. The strategy was successfully applied to a convergent synthesis of the ABCD ring fragment 4 of ciguatoxins, the causative toxin for ciguatera fish poisoning. The synthetic route includes a convergent union of the B and D rings ( 18 and 29c , respectively) by the B -alkyl Suzuki coupling, introduction of a double bond into the D ring followed by reductive closure of the tetrahydropyran C ring to afford the BCD ring system 51 , and, finally, ring-closing metathesis reaction to construct the oxepene A ring.

Stereoselective Synthesis of Substituted Tetrahydropyrans via Domino Olefin Cross-Metathesis/Intramolecular Oxa-Conjugate Cyclization

A novel strategy for the stereoselective synthesis of substituted tetrahydropyrans has been developed on the basis of a domino olefin cross-metathesis/intramolecular oxa-conjugate cyclization catalyzed by the Hoveyda-Grubbs second-generation catalyst.

Total Synthesis and Biological Evaluation of (+)‐Neopeltolide and Its Analogues

The stereocontrolled total synthesis of the originally proposed (1) and correct (2) structures of (+)-neopeltolide, a novel marine macrolide natural product with highly potent antiproliferative activity against several cancer cell lines as well as potent antifungal activity, has been achieved by exploiting a newly developed Suzuki-Miyaura coupling/ring-closing metathesis strategy. Alkylborate 44, which was generated in situ from iodide 34, was coupled with enol phosphate 8 by a Suzuki-Miyaura coupling. Ring-closing metathesis of the derived diene 45 followed by stereoselective hydrogenation afforded tetrahydropyran 47 as a single stereoisomer in high overall yield from 34. Our convergent strategy enabled us to construct the 14-membered macrolactone core structure of 2 in a rapid and efficient manner. Total synthesis and biological evaluation of synthetic intermediates and designed synthetic analogues, performed to establish the structure-activity relationships of 2, led to the discovery of a structurally simple yet potent cytotoxic analogue, 9-demethylneopeltolide (54).

Total Synthesis and Biological Assessment of (−)‐Exiguolide and Analogues

We describe herein an enantioselective total synthesis of (-)-exiguolide, the natural enantiomer. The methylene bis(tetrahydropyran) substructure was efficiently synthesized by exploiting olefin cross-metathesis for the assembly of readily available acyclic segments and intramolecular oxa-conjugate cyclization and reductive etherification for the formation of the tetrahydropyran rings. The 20-membered macrocyclic framework was constructed in an efficient manner by means of Julia-Kocienski coupling and Yamaguchi macrolactonization. Finally, the (E,Z,E)-triene side chain was introduced stereoselectively via Suzuki-Miyaura coupling to complete the total synthesis. Assessment of the growth inhibitory activity of synthetic (-)-exiguolide against a panel of human cancer cell lines elucidated for the first time that this natural product is an effective antiproliferative agent against the NCI-H460 human lung large cell carcinoma and the A549 human lung adenocarcinoma cell lines. Moreover, we have investigated structure-activity relationships of (-)-exiguolide, which elucidated that the C5-methoxycarbonylmethylidene group and the length of the side chain are important for the potent activity.