Unique Reactivity of the 1,4-Bis(silyloxy)-1,3-cyclopentadiene Moiety: Application to the Synthesis of 7-Norbornanone Derivatives.

We describe a method for the synthesis of various 2-silyloxy-2-norbornen-7-ones by exploiting the specific reactivity of the 1,4-bis(silyloxy)-1,3-cyclopentadiene framework, which is generated by the silylation of a 2,2-disubstituted-1,3-cyclopentanedione bearing a picolinoyloxy group at the 2' position of its C-2 side chain. The release of the acyloxy group during the reaction generates carbocations that are then attacked by silyloxy-substituted carbons in the 1,4-bis(silyloxy)-1,3-cyclopentadiene moiety skeleton, forming a 4,5-cis-fused ring skeleton. Skeletal rearrangement of the bicyclic core results in the formation of the corresponding 2-silyloxy-2-norbornen-7-one. This novel transformation of 1,3-cyclopentanedione moieties can be used to synthesise other cyclopentenone-fused bicyclic frameworks.

Alcohol synthesis based on the SN2 reactions of alkyl halides with the squarate dianion.

A convenient method has been developed for transforming alkyl halides into the corresponding alcohols via an SN2 reaction. Treatment of an alkyl halide with the squarate dianion at high temperature produces mono-alkyl squarate, and a one-pot basic hydrolysis of the intermediate affords the alcohol in good yield.

Diastereoselective Synthesis of trans-anti-Hydrophenanthrenes via Ti-mediated Radical Cyclization and Total Synthesis of Kamebanin.

Ent-kaurenes consist of an ABC-ring based on a trans-anti-hydrophenanthrene skeleton and a D ring with an exomethylene. Highly oxygen-functionalized ent-kauren-15-ones have promising antiinflammatory pharmacological activity. In this study, we developed a novel diastereoselective synthesis of trans-anti-hydrophenanthrenes via a Ti-mediated reductive radical cyclization. We also demonstrated the applicability of this method by developing the first total synthesis of (±)-kamebanin (longest linear sequence; 17 steps, overall yield; 6.5 %). Furthermore, this synthesis provided a formal semi-pinacol rearrangement for the construction of the quaternary carbon at C8 and a novel Thorpe-Ziegler-type reaction for the construction of the D-ring.

Model Synthetic Study of Tutin, a Picrotoxane-Type Sesquiterpene: Stereoselective Construction of a cis-Fused 5,6-Ring Skeleton.

Picrotoxinin, coriamyrtin, and tutin are representative natural products classified as picrotoxane-type sesquiterpenes and they function as strong neurotoxins. Because they possess a cis-fused 5,6-ring skeleton with a highly congested functionalization, organic chemistry researchers have pursued the development of a stereoselective synthesis method for such skeleton. This study aims to stereoselectively synthesize the cis-fused 5,6-ring skeleton with two tetrasubstituted carbons at both angular positions using a model compound. The results revealed that the desymmetrization of the 2-methyl-1,3-cyclopentanedione moiety via the DL-proline-mediated intramolecular aldol reaction of a pentanal derivative bearing an isopropenyl group and the five-membered ring at the 3- and 5-position, respectively, provided the desired cis-fused skeleton. This reaction can construct four contiguous stereogenic centers of the bicyclic skeleton with the two angular positions in good yield with high stereoselectivity. Further, this reaction was applied to the kinetic resolution of the racemate using L-proline, providing the enantiomeric pure aldol product with the desired skeleton. This method can be utilized for total synthesis of picrotoxane-type sesquiterpenes.

Lipid Droplet Formation Is Regulated by Ser/Thr Phosphatase PPM1D via Dephosphorylation of Perilipin 1.

Hypertrophy and hyperplasia of white adipocytes induce obesity, leading to diseases such as type 2 diabetes and hypertension, and even cancer. Hypertrophy of white adipocytes is attributed to the excessive storage of the energy form of triglycerides in lipid droplets (LDs). LDs are fat storage organelles that maintain whole-body energy homeostasis. It is important to understand the mechanism of LD formation for the development of obesity therapy; however, the regulatory mechanisms of LD size and formation are not fully understood. In this study, we demonstrated that the PPM family phosphatase PPM1D regulates LD formation. PPM1D specific inhibitor, SL-176 significantly decreased LD formation via two different pathways: dependent of and independent of adipocyte-differentiation processes. In the mature white adipocytes after differentiation, LD formation was found to be controlled by PPM1D via dephosphorylation of Ser511 of perilipin 1. We found that inhibition of PPM1D in mature white adipocytes significantly reduced the size of the LDs via dephosphorylation of Ser511 of perilipin 1 but did not change the lipolysis sensitivity and the total amount of lipid in cells. Collectively, the results of this study provide evidence that PPM1D plays an important role in LD formation in mature adipocytes.

Biomimetic Total Syntheses of (+)-Chloropupukeananin, (-)-Chloropupukeanolide D, and Chloropestolides.

Chloropupukeananin, chloropupukeanolides, and chloropestolides are a family of structurally complex bioactive natural products that possess highly functionalized tricyclo[4.3.1.03,7]decane or bicyclo[2.2.2]octane skeletons. Biosynthesis of the chloropupukeananin family is triggered by the intermolecular heterodimeric Diels-Alder reaction between maldoxin and iso-A82775C; however, the enzymes involved have not yet been identified. We herein report the one-pot biomimetic synthesis of chloropupukeananin and chloropupukeanolide D. Moreover, the effect of the solvent on the intermolecular Diels-Alder reaction of siccayne and maldoxin suggested that the biosynthesis of the chloropupukeananin family involves a Diels-Alderase-catalyzed heterodimeric Diels-Alder reaction.

Formal Total Synthesis of Atropurpuran.

Atropurpuran, isolated from the roots of Aconitum hemsleyanum, is a non-alkaloidal diterpene which possesses a unique pentacyclic skeleton that contains an unprecedented tetracyclo[5.3.3.04,9.04,12]tridecane unit. We report herein the formal total synthesis of atropurpuran. The key features of our synthetic route are a high diastereoselective construction of the tri- and tetrasubstituted carbons (i.e., C4, C5, C10, and C20) through an Yb-catalyzed Mukaiyama aldol reaction in an aqueous medium and a one-pot operation including an intramolecular Diels-Alder reaction/ring-closing metathesis to construct the unique pentacyclic skeleton of atropurpuran.

Asymmetric Total Synthesis of Brasilicardins.

Brasilicardins, bacterial diterpenoid natural products that display highly potent immunosuppressive activity, are promising immunosuppressant drug candidates. Structurally, they can be described as hybrids of terpenoids, amino acids, and saccharides, and share a characteristic highly strained anti-syn-anti-fused perhydrophenanthrene terpenoid scaffold (ABC-ring system) with two quaternary asymmetric carbon atoms. A unified and stereoselective total synthesis of all four brasilicardins has been designed based on the strategic use of an intramolecular conjugate addition. The ABC-ring system was initially constructed with high stereocontrol by novel intramolecular conjugate additions of Weinreb amides and in situ generated (Z)-vinyl copper species. The late-stage common intermediate was subjected to stereoselective installation of the amino acid component, followed by introduction of the saccharide unit via glycosylation to accomplish the total synthesis of brasilicardins A-D. Our synthesis offers opportunities to synthesize various brasilicardin analogues for biological and pharmacological investigations.

Functional 1,3a,6a-triazapentalene scaffold: Design of fluorescent probes for kinesin spindle protein (KSP).

1,3a,6a-Triazapentalene is a compact fluorescent chromophore. In this study, triazapentalene was used to modify a series of biphenyl-type inhibitors of kinesin spindle protein (KSP) to develop fluorescent probes for the intracellular visualization of this protein. Microscopic studies demonstrated that these novel triazapentalene-labeled compounds exhibited inhibitory activity towards KSP in cultured cells and provided important information concerning the intracellular distribution.

Substituent Effect at the C4-Position of 1,3a,6a-Triazapentalene.

Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-position were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C4-position allowed a long-wavelength shift of the fluorescence maximum. Furthermore, the phenyl group at the C4-position was found to induce a substantial increase in the extinction coefficient value.

Novel inhibitors targeting PPM1D phosphatase potently suppress cancer cell proliferation.

Protein phosphatase magnesium-dependent 1δ (PPM1D, Wip1) is a p53 inducible serine/threonine phosphatase. PPM1D is a promising target protein in cancer therapy since overexpression, missense mutations, truncating mutations, and gene amplification of PPM1D are reported in many tumors, including breast cancer and neuroblastoma. Herein, we report that a specific inhibitor, SL-176 that can be readily synthesized in 10 steps, significantly inhibits proliferation of a breast cancer cell line overexpressing PPM1D and induces G2/M arrest and apoptosis. SL-176 decreases PPM1D enzyme activity potently and specifically in vitro. These results demonstrate that SL-176 could be a useful lead compound in the development of effective anti-cancer agents.

Inhibition of C-terminal truncated PPM1D enhances the effect of doxorubicin on cell viability in human colorectal carcinoma cell line.

PPM1D is a p53-inducible Ser/Thr phosphatase. One of the main functions of PPM1D in normal cells is to act as a negative regulator of the p53 tumor suppressor by dephosphorylating p53 and several kinases. PPM1D is considered an oncoprotein owing to both its functions and the fact that gene amplification and overexpression of PPM1D are reported in several tumors. Recently, PPM1D mutations resulting in C-terminal truncated alterations were found in brainstem gliomas and colorectal cancers, and these mutations enhanced the activity of PPM1D. Therefore, C-terminal truncated PPM1D should be also considered as a potential candidate target of anticancer drugs. Here we showed that combination treatment with PPM1D-specific inhibitor SPI-001 and doxorubicin suppressed cell viability of HCT-116 cells overexpressing C-terminal truncated PPM1D through p53 activation compared with doxorubicin alone. Our results suggest that combination treatment with PPM1D inhibitor and doxorubicin may be a potential anti-cancer treatment in PPM1D-mutated cancer cells.

Synthesis of dihydrotropone derivatives using an anionic 8π-electrocyclic reaction.

A new method to synthesise functionalised cycloheptatrienes was established using the anionic 8π-electrocyclic reaction of ß-ketoester-derived dienyne substrates. The cyclised products were converted to a variety of cycloheptatriene derivatives including tropones. Using this method, a concise, first total synthesis of (-)-orobanone, a natural sesquiterpenoid, was achieved.

Total synthesis of zoanthamine alkaloids.

Zoanthamine alkaloids, isolated from organisms in the Zoanthus genus, constitute a distinctive family of marine metabolites. These molecules exhibit a broad spectrum of unique biological properties. For example, norzoanthamine inhibits interleukin-6, the key mediator of bone resorption in osteoporosis, providing a promising drug candidate for a disease that affects more than 10 million people over age 50 in the United States. In addition, these natural products are characterized by a densely functionalized heptacyclic framework, as exemplified by the structures of zoanthamine, norzoanthamine, and zoanthenol, which makes them extremely attractive targets for chemical synthesis. Prior to our first total synthesis of norzoanthamine in 2004, the densely functionalized and complex stereostructures of the zoanthamine alkaloids had impeded synthetic studies of these molecules. In this Account, we describe our synthetic approach toward the total synthesis of zoanthamine alkaloids, focusing on how we overcame various synthetic challenges. At the beginning of our synthetic studies, we aimed to develop an efficient route that was flexible enough to provide access to several members of the family while allowing the synthesis of various analogues for biological testing. Our first project was the total synthesis of norzoanthamine, and we established an efficient synthetic route based on a novel strategy involving the following key features. First, we used a sequential three-component coupling reactions and subsequent photosensitized oxidation of a furan moiety to synthesize the precursor for the key intramolecular Diels-Alder reaction. Second, the key intramolecular Diels-Alder reaction constructed the ABC-ring carbon framework bearing two adjacent quaternary asymmetric carbon atoms at the C12 and C22 positions in a single stereoselective step. Third, we installed the third quaternary asymmetric carbon center at the C9 position by an intramolecular acylation of a keto alcohol followed by successive O-methylation and C-methylation reactions with complete stereoselectivity. Through the exploitation of a deuterium kinetic isoptope effect, we then efficiently synthesized the alkyne segment. Next, a coupling reaction between the alkyne segment and the amino alcohol segment and several subsequent synthetic transformations afforded the bis-aminoacetalization precursor. Finally, bis-aminoacetalization reactions carried out in one-pot constructed the DEFG-ring system and culminated in the total synthesis of norzoanthamine. Our synthetic route to norzoanthamine also allowed access to other zoanthamine alkaloids from a common synthetic intermediate, by way of stereoselective introduction of the C19 methyl group for zoanthamine, and isoaromatization for construction of the aromatic A-ring in zoanthenol. The chemistry described here not only allowed us to overcome formidable synthetic challenges but also opened a completely chemical avenue to naturally occurring zoanthamine alkaloids and their synthetic derivatives.

Total Synthesis of (+)-Coriamyrtin via a Desymmetrizing Strategy Involving a 1,3-Cyclopentanedione Moiety.

We describe the total synthesis of (+)-coriamyrtin, which bears a highly functionalized cis-hydrindane skeleton and is a widely known neurotoxin of the Coriariaceae family. Our synthetic strategy involves the highly stereoselective construction of the cis-hydrindane skeleton via a desymmetrizing strategy involving a 1,3-cyclopentanedione moiety using an intramolecular aldol reaction and the formation of the 1,3-diepoxide moiety of coriamyrtin through the elaborate functionalization of the cyclopentane ring in the bicyclic structure.

Solanoeclepin B, a hatching factor for potato cyst nematode.

The potato cyst nematode (PCN) causes extensive crop losses worldwide. Because the hatching of PCN requires host-derived molecules known as hatching factors (HFs), regulating HF production in host plants may help to control this harmful pest. Solanoeclepin A (SEA), isolated from potato, is the most active HF for PCN; however, its biosynthesis is completely unknown. We discovered a HF called solanoeclepin B (SEB) from potato and tomato root exudates and showed that SEB was biosynthesized in the plant and converted to SEA outside the plant by biotic agents. Moreover, we identified five SEB biosynthetic genes encoding three 2-oxoglutarate-dependent dioxygenases and two cytochrome P450 monooxygenases in tomato. Exudates from tomato hairy roots in which each of the genes was disrupted contained no SEB and had low hatch-stimulating activity for PCN. These findings will help to breed crops with a lower risk of PCN infection.

A small molecule inhibitor of p53-inducible protein phosphatase PPM1D.

PPM1D is a p53-inducible Ser/Thr protein phosphatase. PPM1D gene amplification and overexpression have been reported in a variety of human tumors, including breast cancer and neuroblastoma. Because the phosphatase activity of PPM1D is essential for its oncogenic role, PPM1D inhibitors should be viable anti-cancer agents. In our current study, we showed that SPI-001 was a potent and specific PPM1D inhibitor. SPI-001 inhibited PPM1D phosphatase activity in PPM1D-overexpressing human breast cancer cells and increased phosphorylation of p53. Furthermore, SPI-001 suppressed cell proliferation by inducing apoptosis. Our present study suggested that SPI-001 was a potential lead compound in developing anti-cancer drugs.

Stereocontrolled synthesis of carbocyclic compounds with a quaternary carbon atom based on SN2' alkylation of γ,δ-epoxy-α,ß-unsaturated ketones.

We developed a new method for stereoselective construction of an all-carbon quaternary stereogenic center on a carbocyclic ring based on regio- and stereoselective S(N)2' alkylation reactions of γ,δ-epoxy-α,ß-unsaturated cyclic ketones. Treatment of the ketones, which were readily prepared in enantiomerically pure form by means of aldol condensations between 3-ethoxy-2-cycloalkenones and α,ß-epoxy aldehydes, with a R(2)Zn-CuCN reagent afforded anti-S(N)2' products stereoselectively. Conversely, the corresponding syn-S(N)2' products were stereoselectively obtained through two-step transformations of the same γ,δ-epoxy-α,ß-unsaturated cyclic ketones: (1) conversion of the epoxide moiety to a chlorohydrin by treatment with MgCl(2) and (2) subsequent S(N)2' substitution of the chlorohydrin with a R(2)Zn-CuCN reagent. These substitution products with their chiral trans-allylic alcohol moieties are promising precursors for complex molecules. For example, Eschenmoser-Claisen rearrangement of one of the substitution products resulted in stereoselective formation of a keto amide having contiguous quaternary and tertiary stereogenic centers.

Total Synthesis of 2-Isocyanoallopupukeanane: Construction of Caged Skeleton by Intramolecular Alkylation of Bromonitriles.

A new method for constructing the bicyclo[3.2.1]octane skeleton was developed by the intramolecular alkylation of a nitrile-side-chain-containing cyclohexanone derivative. The cyclization precursors were prepared via the stereoselective bromination of the triisopropylsilyl enol ethers of 4-substituted cyclohexanones. Upon treatment with LiNEt2, the bromonitriles underwent a stereoselective intramolecular SN2 reaction to afford bicyclo[3.2.1]octane derivatives with a cyano group on the convex face. The total synthesis of 2-isocyanoallopupukeanane (6.5% yield) from methyl vinyl ketone was accomplished via a 17-step transformation.