Photo-oxygenation by a biocompatible catalyst reduces amyloid-ß levels in Alzheimer's disease mice.

Amyloid formation and the deposition of the amyloid-ß peptide are hallmarks of Alzheimer's disease pathogenesis. Immunotherapies using anti-amyloid-ß antibodies have been highlighted as a promising approach for the prevention and treatment of Alzheimer's disease by enhancing microglial clearance of amyloid-ß peptide. However, the efficiency of antibody delivery into the brain is limited, and therefore an alternative strategy to facilitate the clearance of brain amyloid is needed. We previously developed an artificial photo-oxygenation system using a low molecular weight catalytic compound. The photocatalyst specifically attached oxygen atoms to amyloids upon irradiation with light, and successfully reduced the neurotoxicity of aggregated amyloid-ß via inhibition of amyloid formation. However, the therapeutic effect and mode of actions of the photo-oxygenation system in vivo remained unclear. In this study, we demonstrate that photo-oxygenation facilitates the clearance of aggregated amyloid-ß from the brains of living Alzheimer's disease model mice, and enhances the microglial degradation of amyloid-ß peptide. These results suggest that photo-oxygenation may represent a novel anti-amyloid-ß strategy in Alzheimer's disease, which is compatible with immunotherapy.

A novel translation inhibitor, mersicarpine, inhibits S-phase progression and induces apoptosis in HL60 cells.

Mersicarpine is an aspidosperma alkaloid isolated from the Kopsia genus of plants. Its intriguing structural features have attracted much attention in synthetic organic chemistry, but no biological activity has been reported. Here, we report the effects of mersicarpine on human leukemia cell line HL60. At concentrations above 30 µm, mersicarpine reversibly arrested cell cycle progression in S-phase. At higher concentrations, it induced not only production of reactive oxygen species, but also apoptosis. Macromolecular synthesis assay revealed that mersicarpine specifically inhibits protein synthesis. These results suggest that mersicarpine is a novel translation inhibitor that induces apoptosis.

Total Synthesis of Haliclonin†A.

The total synthesis of haliclonin A was accomplished. Starting from 3,5-dimethoxybenzoic acid, a functionalized cyclohexanone fused to a 17-membered ring was prepared through a Birch reduction/alkylation sequence, ring-closing metathesis, intramolecular cyclopropanation, and stereoselective 1,4-addition of an organocopper reagent to an enone moiety. Reductive C-N bond formation via an N,O-acetal forged the 3-azabicyclo[3.3.1]nonane core. The allyl alcohol moiety was constructed by a sequence involving stereoselective α-selenylation of an aldehyde via an enamine, syn-elimination of a selenoxide, and allylation of the aldehyde with an allylboronate. Formation of the 15-membered ring containing a skipped diene was achieved by ring-closing metathesis, and final transformations led to the synthesis of haliclonin A.

Total Synthesis of Tetrodotoxin.

A total synthesis of tetrodotoxin was accomplished. A Diels-Alder reaction between a known enone and a siloxy diene gave a tricyclic product, the steric bias of which was used to construct the remaining stereogenic centers. A nitrogen atom was introduced either by a four-step sequence involving a Curtius rearrangement, or a three-step sequence featuring a newly developed transformation of a terminal alkyne into a nitrile. Introduction of the guanidine moiety followed by the formation of the heterocyclic system by cascade reactions led to tetrodotoxin.

Synthetic Studies of Isoschizogamine: Alternative Preparation of the Key Intermediate.

An alternative synthetic route toward a key intermediate in the total synthesis of isoschizogamine is described. The Claisen-Johnson rearrangement stereoselectively constructed a quaternary carbon. Trifluoroperacetic acid mediated the Baeyer-Villiger oxidation to form a bicyclic lactone. The Mukaiyama-Matsuo protocol converted the lactone into an α,ß-unsaturated lactone, that was used as the substrate for the rhodium-mediated 1,4-addition of an arylboronic acid.

BIN1 regulates BACE1 intracellular trafficking and amyloid-ß production.

BIN1 is a genetic risk factor of late-onset Alzheimer disease (AD), which was identified in multiple genome-wide association studies. BIN1 is a member of the amphiphysin family of proteins, and contains N-terminal Bin-Amphiphysin-Rvs and C-terminal Src homology 3 domains. BIN1 is widely expressed in the mouse and human brains, and has been reported to function in the endocytosis and the endosomal sorting of membrane proteins. BACE1 is a type 1 transmembrane aspartyl protease expressed predominantly in neurons of the brain and responsible for the production of amyloid-ß peptide (Aß). Here we report that the depletion of BIN1 increases cellular BACE1 levels through impaired endosomal trafficking and reduces BACE1 lysosomal degradation, resulting in increased Aß production. Our findings provide a mechanistic role of BIN1 in the pathogenesis of AD as a novel genetic regulator of BACE1 levels and Aß production.

Synthesis of the [7-5-5] tricyclic core of Daphniphyllum alkaloids.

The [7-5-5] tricyclic core of the Daphniphyllum alkaloids was constructed, featuring a Claisen-Ireland rearrangement to install the two contiguous stereogenic centers, E1cB elimination to form the tetrasubstituted C-C double bond, and a 2,3-Wittig rearrangement to construct the quaternary carbon. Ring-closing metathesis and an intramolecular carbonyl ene reaction were employed for construction of the requisite ring system.

Total Synthesis of (-)-Morphine.

Asymmetric total synthesis of (-)-morphine has been accomplished in 18 steps from commercially available 7-methoxy-2-tetralone. Our synthesis features a simple transformation from a readily prepared chiral intermediate, construction of the E-ring by acid-mediated cyclization, and singlet oxygen-mediated manipulation of the C-ring. Transformation of the final stage involves construction of the morphinan skeleton by means of 1,6-addition of in situ generated secondary amine.

Allosteric regulation of γ-secretase activity by a phenylimidazole-type γ-secretase modulator.

γ-Secretase is an intramembrane-cleaving protease responsible for the generation of amyloid-ß (Aß) peptides. Recently, a series of compounds called γ-secretase modulators (GSMs) has been shown to decrease the levels of long toxic Aß species (i.e., Aß42), with a concomitant elevation of the production of shorter Aß species. In this study, we show that a phenylimidazole-type GSM allosterically induces conformational changes in the catalytic site of γ-secretase to augment the proteolytic activity. Analyses using the photoaffinity labeling technique and systematic mutational studies revealed that the phenylimidazole-type GSM targets a previously unidentified extracellular binding pocket within the N-terminal fragment of presenilin (PS). Collectively, we provide a model for the mechanism of action of the phenylimidazole-type GSM in which binding at the luminal side of PS induces a conformational change in the catalytic center of γ-secretase to modulate Aß production.

Total Syntheses of Aurachins†A and B.

Aurachins A and B are alkaloids having 3-hydroxyquinoline N-oxide cores. An efficient method for the synthesis of 3-hydroxyquinoline N-oxides was established and is amenable to the total syntheses of aurachins A and B. Alkylation of 1-(2-nitrophenyl)butan-2-one with farnesyl bromide took place selectively at the benzylic position, and subsequent treatment of the alkylated product with sodium tert-butoxide in dimethyl sulfoxide gave aurachin B. Alkylation of 1-(2-nitrophenyl)butan-2-one with an epoxy iodide derived from farnesol was used to access aurachin A.

Total Synthesis of (-)-Tetrodotoxin and 11-norTTX-6(R)-ol.

The enantioselective total synthesis of (-)-tetrodotoxin [(-)-TTX] and 4,9-anhydrotetrodotoxin, which are selective blockers of voltage-gated sodium channels, was accomplished from the commercially available p-benzoquinone. This synthesis was based on efficient stereocontrol of the six contiguous stereogenic centers on the core cyclohexane ring through Ogasawara's method, [3,3]-sigmatropic rearrangement of an allylic cyanate, and intramolecular 1,3-dipolar cycloaddition of a nitrile oxide. Our synthetic route was applied to the synthesis of the tetrodotoxin congeners 11-norTTX-6(R)-ol and 4,9-anhydro-11-norTTX-6(R)-ol through late-stage modification of the common intermediate. Neutral deprotection at the final step enabled easy purification of tetrodotoxin and 11-norTTX-6(R)-ol without competing dehydration to their 4,9-anhydro forms.

Enantioselective Total Synthesis of (+)-Hinckdentine A via a Catalytic Dearomatization Approach.

Optically pure hinckdentine A was synthesized on a 300 mg scale via an asymmetric catalysis-based strategy. The key steps to the first asymmetric synthesis involved (i) enantioselective dearomative cyclization of an achiral N-acyl indole that allowed for the efficient construction of the key polycyclic indoline intermediate with a crucial tetrasubstituted stereogenic carbon center, (ii) Beckmann fragmentation-mediated ring expansion, (iii) rearrangement-based introduction of an anilinic nitrogen atom, (iv) regioselective tribromination, and (v) final closure of the cyclic amidine moiety.

Eudistomin C, an Antitumor and Antiviral Natural Product, Targets 40S Ribosome and Inhibits Protein Translation.

Eudistomin C (EudiC), a natural product, shows potent antitumor and antiviral activities, but the target molecule and the mechanism of action remain to be revealed. Here, we show that the 40S ribosome is the target in EudiC cytotoxicity. We isolated EudiC-resistant mutants from a multidrug-sensitive yeast strain, and a genetic analysis classified these YER (yeast EudiC resistance) mutants into three complementation groups. A genome-wide study revealed that the YER1-6 mutation is in the uS11 gene (RPS14A). Biotinylated EudiC pulled down Rps14p-containing complexes from 40S and 80S ribosomes, but not from the 60S ribosome. EudiC strongly inhibited translation of the wild-type strain but not of YER1-6 in cells and in vitro. These results indicate that EudiC is a protein synthesis inhibitor targeting the uS11-containing ribosomal subunit, and shows cytotoxicity by inhibiting protein translation.

Antiproliferative Activity of Amathaspiramide Alkaloids and Analogs.

Assisted by the total syntheses of all the amathaspiramides, six natural products and four synthetic intermediates with partially fluctuating structures were prepared and subjected to a growth inhibition assay in four human cancer cell lines. The results showed amathaspiramides A, C, and E had moderate antiproliferative activity. Examination of the structure-activity relationship revealed the importance of the amine or imine substructure on the pyrrolidine moiety and the 8R stereochemistry on the N-acyl hemiaminal moiety for the antiproliferative activity of amathaspiramide alkaloids.

Chemical Transformation of an Intermediate in the Synthesis of Huperzine A, Leading to a Diverse Array of Molecules.

Chemical transformation of an early intermediate in our synthesis of huperzine A provided a diverse array of molecules in which a variety of functional groups could be embedded.

Conversion of Vindoline into 11-Mesyloxytabersonine.

Conversion of readily available vindoline to 11-mesyloxytabersonine, a versatile synthetic intermediate for indole alkaloids, has been achieved by a 9-step sequence in 39% overall yield.

Total Synthesis of (-)-Daphenylline.

Total synthesis of (-)-daphenylline, a hexacyclic Daphniphyllum alkaloid, was achieved. Construction of the tricyclic DEF ring system was initiated by asymmetric Negishi coupling followed by an intramolecular Friedel-Crafts reaction. Installation of a side chain onto the tricyclic core was carried out through Sonogashira coupling, stereocontrolled Claisen rearrangement by taking advantage of the characteristic conformation of the tricyclic DEF core, and the stereoselective alkylation of a lactone. After the introduction of a glycine unit, the ABC ring system was stereoselectively constructed through intramolecular cycloaddition of the cyclic azomethine ylide.

Development of a Divergent Synthetic Route to the Erythrina Alkaloids: Asymmetric Syntheses of 8-Oxo-erythrinine, Crystamidine, 8-Oxo-erythraline, and Erythraline.

A general synthetic methodology toward the erythrina alkaloids has been developed. Inspired by a proposed biosynthetic mechanism, the medium-sized chiral biaryl lactam was asymmetrically transformed into the common core A-D rings by a stereospecific singlet oxygen oxidation of the phenol moiety, followed by a transannular aza-Michael reaction to the dienone functionality. The late-stage manipulation of the oxidation and oxygenation states of the functional groups on the peripheral moieties enabled the flexible syntheses of the erythrina alkaloids.

Phenylpiperidine-type γ-secretase modulators target the transmembrane domain 1 of presenilin 1.

Amyloid-ß peptide ending at the 42nd residue (Aß42) is implicated in the pathogenesis of Alzheimer's disease (AD). Small compounds that exhibit selective lowering effects on Aß42 production are termed γ-secretase modulators (GSMs) and are deemed as promising therapeutic agents against AD, although the molecular target as well as the mechanism of action remains controversial. Here, we show that a phenylpiperidine-type compound GSM-1 directly targets the transmembrane domain (TMD) 1 of presenilin 1 (PS1) by photoaffinity labelling experiments combined with limited digestion. Binding of GSM-1 affected the structure of the initial substrate binding and the catalytic sites of the γ-secretase, thereby decreasing production of Aß42, possibly by enhancing its conversion to Aß38. These data indicate an allosteric action of GSM-1 by directly binding to the TMD1 of PS1, pinpointing the target structure of the phenylpiperidine-type GSMs.

Formal Synthesis of Sarain A: Intramolecular Cycloaddition of an Eight-Membered Cyclic Nitrone to Construct the 2-Azabicyclo[3.3.1]nonane Framework.

An enantioselective route to the tetracyclic skeleton of sarain A has been developed. Asymmetric reduction of an ynone introduced a chiral center which was transferred to the contiguous tertiary stereogenic centers through an Ireland-Claisen rearrangement. The 2-azabicyclo[3.3.1]nonane framework was constructed by an unprecedented intramolecular cycloaddition of an eight-membered cyclic nitrone. Using the steric bias of the bicyclic system, the quaternary carbon atom was constructed by a stereoselective aldol reaction. Further ring formations were performed by ring-closing metathesis for the 13-membered ring and an iodoamidation reaction for the pyrrolidine ring. The present synthesis has successfully provided an alternative route to the late-stage intermediate of Overman's synthesis.