Pd-Catalyzed Stereoselective Construction of Benzo-Fused Decalines with a Quaternary Carbon.

The Pd-catalyzed stereoselective construction of decalins with one-carbon units bearing heteroatoms at the ring junction is described. The Pd-catalyzed cyclization of silyl enol ether resulted in exclusive formation of the cis isomer (89%, >100/1 cis/trans). On the contrary, Pd-catalyzed carboiodination and carboborylation (with oxidative workup) provided products in 56% yield (1/>100 cis/trans) and 69% yield (1/11 cis/trans), respectively.

Scabronine G Methyl Ester Improves Memory-Related Behavior and Enhances Hippocampal Cell Proliferation and Long-Term Potentiation via the BDNF-CREB Pathway in Olfactory Bulbectomized Mice.

A previous study reported that scabronine G methyl ester (SG-ME) potentially enhances the in vitro secretion of neurotrophic factors such as nerve growth factor via the protein kinase C (PKC)-ζ pathway. However, it remains unknown whether SG-ME can improve cognitive dysfunctions in olfactory bulbectomized (OBX) mice. To address this question, we evaluated SG-ME-treated and untreated OBX mice in a passive avoidance test. We also investigated potential effects of SG-ME on several parameters: cell proliferation and cAMP response element-binding protein (CREB) phosphorylation in the hippocampal dentate gyrus by immunohistochemistry, brain-derived neurotrophic factor (BDNF) levels in the hippocampus by Western blotting, p-CREB levels in the hippocampus by MapAnalyzer, and long-term potentiation (LTP) by electrophysiology. On the 14th day after surgery OBX mice showed altered passive avoidance and decreases in both cell proliferation and long-term potentiation in the hippocampus, while these changes were reversed by SG-ME (20 µg/mouse) 24 h after the treatment. The improvement in memory deficits was prevented when SG-ME was co-administeredwith either zeta inhibitory peptide (PKC-ζ inhibitor), anti-BDNF antibody, ANA-12 (TrkB antagonist), U0126 (MEK inhibitor), H-89 (PKA inhibitor), LY294002 (PI3K inhibitor) or KN-93 (CaMKII inhibitor). We found that SG-ME enhanced brain-derived neurotrophic factor and p-CREB levels in the hippocampus while p-CREB was localized in neurons, but not in astrocytes nor microglial cells. These findings revealed the potential of SG-ME in improving memory impairments by enhancing cell proliferation and LTP via activation of the BDNF/CREB signaling pathway in neurons.

Enantioselective Total Synthesis of Cotylenin A.

A convergent enantioselective total synthesis of cotylenin A is described. The A-ring fragment, prepared via the catalytic asymmetric intramolecular cyclopropanation developed in our laboratory, and the C-ring fragment, prepared from a known chiral compound via a modified acyl radical cyclization, were successfully assembled by the Utimoto coupling reaction. The formidable carbocyclic eight-membered ring of cotylenin A was efficiently constructed by a palladium-mediated cyclization. All the hydroxy groups in the scaffold were stereoselectively introduced, and a modified reducing reagent, Me4NBH(O2CiPr)3, has been developed. The sugar moiety fragment was prepared via three consecutive carbon-oxygen bond-forming reactions, and the glycosylation was accomplished using Wan's protocol.

Palladium-Catalyzed Carbothiolation via Trapping of the σ-Alkyl Palladium Intermediate with RSTIPS.

A palladium-catalyzed carbothiolation via the reaction of a σ-alkyl palladium intermediate with a TIPS thioether is described. It was found that the use of Cs2CO3, (IPr)Pd(allyl)Cl, and a TIPS thioether was key to obtaining alkyl aryl and dialkyl sulfides in high yield through the reaction of a σ-alkyl palladium intermediate. The developed reaction is applicable to a wide range of substrates and thiols.

Synthesis and Reaction of ortho-Benzoquinone Monohemiaminals.

The preparation and reactions of ortho-benzoquinone monohemiaminals are described. The oxidative dearomatization of phenols bearing amino alcohol groups induced N-cyclization to afford ortho-benzoquinone monohemiaminals. The N-cyclization stereoselectively affords the product when a chiral amino alcohol is used as the substituent. The chiral ortho-benzoquinone monohemiaminal undergoes stereoselective Diels-Alder reactions with electron-deficient alkenes, as expected, confirming the promising utility of ortho-benzoquinone monohemiaminals.

Enantio- and Stereoselective Construction of Atisane Scaffold via Organocatalytic Intramolecular Michael Reaction and Diels-Alder Reaction.

An enantio- and stereoselective construction of the atisane scaffold via organocatalytic intramolecular Michael reaction and Diels-Alder reaction is described. The organocatalytic intramolecular Michael reaction has been found to stereoselectively generate a trans-stereodiad comprising an all-carbon quaternary and a tertiary stereogenic centers. Use of the chiral secondary amine bearing thiourea with benzoic acid as additive is the key to obtaining the desired product with excellent ee in synthetically acceptable yield. The prepared chiral building block has been successfully converted to the compound including the atisane scaffold via the highly stereoselective intramolecular Diels-Alder reaction.

Enantioselective Mukaiyama-Michael Reaction of Cyclic α-Alkylidene ß-Keto Phosphine Oxide and Phosphonate and Asymmetric Synthesis of (R)-Homosarkomycin.

The asymmetric Mukaiyama-Michael reaction of cyclic α-alkylidene ß-oxo phosphates and phosphine oxides that proceeds in a highly enantioselective manner is described. It is possible to carry out these reactions using a catalytic amount of a bisoxazoline-Cu(II) complex without decreasing the enantioselectivity, and one of the products has been successfully used for the first enantioselective synthesis of (R)-homosarkomycin.

Enantioselective approach to polycyclic polyprenylated acylphloroglucinols via catalytic asymmetric intramolecular cyclopropanation.

The formal enantioselective total synthesis of nemorosone, garsubellin A, clusianone, and hyperforin is described. The catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of an α-diazo ketone, a common synthetic intermediate for the above four polycyclic polyprenylated acylphloroglucinols previously reported by us, exhibited low enantioselectivity. However, CAIMCP of the corresponding α-diazo ß-keto sulfone afforded the desired product in 79% yield with 84% ee. Investigation of the CAIMCP of the α-diazo ß-keto sulfone demonstrated the formation of a rearrangement product in the presence of molecular sieves 4 Å, whereas, in the presence of H2O, the byproduct derived from ring-opening of the desired cyclopropane was observed. X-ray crystallographic analysis suggested that the above two products are derived from the same chiral intermediate. The product derived from ring-opening of the cyclopropane was successfully transformed to the respective synthetic intermediates for the total syntheses of nemorosone, garsubellin A, clusianone, and hyperforin, which had previously been reported by us.

Highly enantioselective catalytic asymmetric [2+2] cycloadditions of cyclic α-alkylidene ß-oxo imides with ynamides.

Highly enantioselective catalytic asymmetric [2+2] cycloadditions of cyclic α-alkylidene ß-oxo imides with ynamides are described. The high reactivity of the cyclic α-alkylidene ß-oxo imide allows the [2+2] cycloadditions of a hindered substrate with unreactive ynamides at low temperature. The X-ray crystallographic analysis of the product suggests that the enantioselectivity of the [2+2] cycloaddition can be well explained by the chelate model comprising the intramolecular hydrogen bond, wherein the cyclic α-alkylidene ß-oxo imide coordinates with Cu(II) through the two imide carbonyls. The imide group in the product can be transformed to amide, nitrile, and ester groups; moreover, it is removable.

Formal total synthesis of (-)-taxol through Pd-catalyzed eight-membered carbocyclic ring formation.

A formal total synthesis of (-)-taxol by a convergent approach utilizing Pd-catalyzed intramolecular alkenylation is described. Formation of the eight-membered carbocyclic ring has been a problem in the convergent total synthesis of taxol but it was solved by the Pd-catalyzed intramolecular alkenylation of a methyl ketone affording the cyclized product in excellent yield (97 %), indicating the high efficiency of the Pd-catalyzed intramolecular alkenylation. Rearrangement of the epoxy benzyl ether through a 1,5-hydride shift, generating the C3 stereogenic center and subsequently forming the C1-C2 benzylidene, was discovered and utilized in the preparation of a substrate for the Pd-catalyzed reaction.

Enantioselective total syntheses of cyathane diterpenoids.

A Personal Account describing the enantioselective total syntheses of cyathane diterpenoids achieved in the Nakada group. A convergent approach to the cyathane scaffold, the [5-6-7] tricyclic carbon skeleton commonly found in cyathane diterpenoids, has been developed using the catalytic asymmetric intramolecular cyclopropanation (CAIMCP) and baker's yeast reduction. This approach has been successfully applied for the enantioselective total syntheses of (+)-allocyathin B2 , (-)-erinacine B, and (-)-erinacine E. The total synthesis of (-)-erinacine E has been achieved via the acyl group migratory intramolecular aldol reaction, which prevents the retro-aldol reaction and allows the construction of the strained structure. The highly efficient and stereoselective total syntheses of (-)-scabronines G, A, D, and (-)-episcabronine A have been achieved via the oxidative dearomatization/inverse electron demand Diels-Alder reaction cascade. Cascade reactions comprising three and five consecutive reactions were employed for the highly efficient total syntheses of (-)-scabronine A and (-)-episcabronine A, respectively.

Collective total synthesis of PPAPs: total synthesis of clusianone via intramolecular cyclopropanation.

The total synthesis of clusianone was accomplished through the stereoselective construction of a bicyclo[3.3.1]nonane derivative via a three-step sequence, which has been utilized for the total syntheses of nemorosone, garsubellin A, and hyperforin: intramolecular cyclopropanation, formation of a geminal dimethyl group, and regioselective ring opening of cyclopropane. Further elaboration, including chemo- and stereoselective hydrogenation to generate the C7 stereogenic center and cross-metathesis to construct prenyl groups in the side-chains, was employed to complete the total synthesis ofclusianone.

Total syntheses of (-)-scabronines†G and A, and (-)-episcabronine†A.

Making scab(ronine)s: The total synthesis of (-)-scabronine G features a highly stereoselective oxidative dearomatization/intramolecular inverse-electron-demand Diels-Alder reaction cascade, and the first total synthesis of (-)-scabronine A comprises a highly stereoselective oxa-Michael/protonation/acetalization cascade. The first total synthesis of (-)-episcabronine A includes another highly stereoselective cascade.

Enantioselective total synthesis of (+)-ophiobolin†A.

The enantioselective total synthesis of (+)-ophiobolin A is described. This total synthesis features the construction of the spiro CD ring of (+)-ophiobolin A through a stereoselective intramolecular Hosomi-Sakurai cyclization reaction, the joining of the A ring to the CD ring by using a reaction reported by Utimoto, and the construction of the ophiobolin eight-membered carbocyclic ring through ring-closing metathesis (RCM), which was performed for the first time in this study. This successful RCM reaction required the use of a substrate that contained either a benzyloxy or a methoxymethoxy group at the C5 position and either an isopropenyl group or its hydroxylated form at the C6 position.

Enantioselective total synthesis of (+)-colletoic acid via catalytic asymmetric intramolecular cyclopropanation of an α-diazo-ß-keto diphenylphosphine oxide.

The enantioselective total synthesis of (+)-colletoic acid, a potent naturally occurring 11ß-hydroxysteroid dehydrogenase type 1 (11ß-HSD1) inhibitor, is described. This total synthesis features a highly enantioselective catalytic asymmetric intramolecular cyclopropanation of an α-diazo-ß-keto diphenylphosphine oxide and five highly stereoselective reactions (cyclopropane opening, Diels-Alder reaction, iodolactonization, alkene formation, and reduction of α,ß-unsaturated carboxylic acid).

Stereoselective total synthesis of garsubellin A.

The stereoselective total synthesis of garsubellin A is described. The total synthesis was achieved through the stereoselective construction of a bicyclo[3.3.1]nonane derivative via a three-step sequence: intramolecular cyclopropanation, formation of a germinal dimethyl group, and regioselective ring opening of cyclopropane. To complete the total synthesis of garsubellin A, chemo- and stereoselective hydrogenation to generate the C8 stereogenic center is followed by the formation of the fused tetrahydrofuran ring by a regioselective epoxide-opening reaction with C3 ketone, and finally cross metathesis to construct two prenyl groups.

Catalytic asymmetric [4 + 2] cycloadditions and Hosomi-Sakurai reactions of α-alkylidene ß-keto imides.

Highly enantioselective catalytic asymmetric reactions of rationally designed α-alkylidene ß-keto imides are described. The [4 + 2] cycloadditions and Hosomi-Sakurai reactions of α-alkylidene ß-keto imides proceed with high enantioselectivity and yield. The [4 + 2] cycloadditions of the imides with various dienes afford products bearing an all-carbon quaternary stereogenic center at the ring junction. α-Alkylidene ß-keto imides should be useful for the enantioselective total synthesis of natural products and other catalytic asymmetric applications.

Preparation of imides via the palladium-catalyzed coupling reaction of organoborons with methyl N-[methoxy(methylthio)methylene]carbamate as a one-carbon elongation reaction.

The preparation of imides via the palladium-catalyzed coupling reaction as a one-carbon elongation reaction is described. The palladium-catalyzed coupling reaction of aryl-, alkyl-, and alkenylborons with N-[methoxy(methylthio)methylene]carbamate in the presence of Cu(I) thiophene-2-carboxylate (CuTC) affords imino ethers that are converted to the corresponding imides by acidic hydrolysis in high yield. The imino ethers are also useful for preparing the corresponding ester without using carbon monoxide.

A non-heme iron(III) complex with porphyrin-like properties that catalyzes asymmetric epoxidation.

In this report, we describe an iron(III) complex containing a carbazole-based tridentate ligand that catalyzes highly enantioselective asymmetric epoxidation of (E)-alkenes at room temperature. The non-heme iron(III) complex has a five-coordinated trigonal-bipyramidal structure, and its two-electron oxidized state has the similar electronic structure as that of iron porphyrins.