論文

A skipped diene（1,4-diene）is an important structural motif found in a variety of biologically active natural products. We report the stereodivergent method, consisting of hydroboration of allenes and the Migita-Kosugi-Stille coupling, which allows for access to all four possible stereo-isomers of the skipped dienes. The hydroboration of allenes is especially useful because both E-allylic and Z-allylic alcohols are obtained by simply changing the organoborane reagent. While use of 9-BBN provides E-allylic alcohols as thermodynamic products, the reaction with HB（Sia）2 gives Z-allylic alcohols as kinetic products. The developed method was successfully applied to the unified total synthesis of madangamine alkaloids.

The full details of the total synthesis of keramaphidin B and ingenamine are reported herein. The most conspicuous transformation in our total synthesis is the base-catalyzed Diels–Alder reaction using dynamic regioselective crystallization (alternatively referred to as crystallization-induced transformation). The tertiary alcohol, which is used for the base-catalyzed activation in the Diels–Alder reaction, is removed as its p-fluorobenzoate using SmI2 (HMPA)4. Double macrocyclic alkylation enables the regioselective construction of two macrocycles in a single step. The developed sequence is highly efficient, achieving the unified total synthesis of keramaphidin B and ingenamine within 13 steps from commercially available compounds. Our biological study elucidated the significant role of the two macrocycles in their antiproliferative effects against human cancer cell lines.

The totally substituted butenolide including two tetrasubstituted olefins is a distinct structural motif seen in Stemona alkaloids, but efficient methods for its synthesis are not well developed. As an ongoing program aimed at the collective total synthesis of the stemoamide group, we report a stereodivergent method to give either (E)-or (Z)-totally substituted butenolide from the same intermediate. While the AgOTf-mediated elimination via the E1-type mechanism results in the formation of the kinetic (Z)-tetrasubstituted olefin, the subsequent TfOH-mediated isomerization gives the thermodynamic (E)-tetrasubstituted olefin. The pyrrole ring is another important structure found in Stemona alkaloids. The direct oxidation of pyrrolidine rings with MnO2 and careful purification give the pyrrole groups without isomerization of the stereocenter in the lactone group. These two methods enable us to synthesize a series of stemoamide-type alkaloids including tricyclic, tetracyclic and pentacyclic frameworks. The anti-inflammatory activities by inhibition of iNOS expression in macrophage cell line RAW264.7 indicate that the most potent anti-inflammatory compounds without cytotoxicity are protostemonines, which consist of pentacyclic frameworks including the totally substituted butenolide.

In the fused tetra cyclic system of the title compound, C29H36O9, the five-membered dioxolane ring adopts a twist conformation; the two adjacent C atoms deviate alternately from the mean plane of the other three atoms by -0.252 (6) and 0.340 (6) Å. The cyclo hexane, cyclo hexene and central cyclo octane rings show chair, half-chair and boat-chair forms, respectively. There are three intra molecular C - H⋯O inter actions supporting the mol ecular conformation, with one S(6) and two S(7) graph-set motifs. In the crystal, inter molecular O - H⋯O hydrogen bonds connect the mol ecules into a helical chain running along the c-axis direction, generating a C(7) graph-set motif. The chains are further linked by inter molecular C - H⋯O inter actions to construct a three-dimensional network. There is no valid C - H⋯π inter action.

Saponins exhibit multiple biological and pharmacological activities, and the sugar moiety of saponins is known to play a crucial role in bioactivity. In this report, we focus on the synthesis and evaluation of saponins with all-nitrogenated sugar (ANS), in which all oxygen atoms are replaced with nitrogen atoms. OSW-1 derivative-, cholesterol-,and diosgenin-ANS glycosides are synthesized by glycosylation with ANS in the presence of TMSOTf. As a result, the OSW-1 mimic, with ANS, exhibits good cytotoxic activity (IC50 = 7.31 ?M) and induces apoptosis.

Direct C-N bond formation from nitroarenes is a valuable synthetic tool for quick access to aniline derivatives. Transformation via nitroso intermediates could be useful due to their unique properties, but the generation of nitrosoarenes in situ from nitroarenes is challenging due to the tendency for various side reactions. Herein we report the photoinduced reductive [4 + 2] cycloaddition of nitroarenes. The method begins with the photoinduced reduction of nitroarenes to give nitrosoarenes by hydrogen atom abstraction (HAA). The generated nitrosoarenes undergo a nitroso Diels-Alder (NDA) reaction. The key to success is the use of N-heterocyclic carbene (NHC) borane, which promotes efficient HAA, enabling the NDA reaction to proceed without the need for transition metals, strong bases, or elevated temperatures. The developed conditions allow high functional group tolerance, enabling late-stage functionalization and further derivatization of biologically active compounds.

A reductive (3+2) annulation of lactams through iridium-catalyzed hydrosilylation and photoredox coupling with α-bromoacetic acid was developed. The iridium-catalyzed hydrosilylation of the lactam carbonyl group and subsequent elimination provide a transient cyclic enamine, which undergoes iridium-catalyzed photoredox coupling with α-bromoacetic acid in a one-pot process. The developed conditions show high functional-group tolerance and provide cyclic N,O-acetals containing a quaternary carbon center. The resulting N,O-acetals undergo a variety of acid-mediated nucleophilic addition reactions via iminium ions to give substituted cyclic amines. The developed sequence including reductive (3+2) annulation and acid-mediated nucleophilic addition was successfully applied to the four-step total synthesis of (±)-eburnamonine.

Synthesis of chiral α, α-disubstituted cyclic nitrones from secondary lactams is reported. The method consists of two stages involving N-oxidation of the lactams and nucleophilic addition to the lactam carbonyls. The N-oxidation of secondary lactams with mCPBA via imidates provides cyclic nitrones with a chiral stereocenter adjacent to the nitrogen atom. A variety of α, α-disubstituted cyclic nitrones were quickly obtained simply by changing organolithium reagents in the nucleophilic addition to N-OSEM lactams.

The total synthesis of isodaphlongamine H based on a lactam strategy, which enables quick access to complex cyclic amines, is described. The strategy begins with alkylation of a chiral lactam and subsequent N-oxidation via an imino ether to afford the N-hydroxylactam. For the key transformation to functionalize the amide carbonyl, an iridium-catalyzed reductive [3 + 2] cycloaddition of the N-hydroxylactam provides a tricyclic isoxazolidine in a one-pot process. After the coupling reaction with an allylic silane fragment, the total synthesis is accomplished through intramolecular Hosomi–Sakurai allylation to construct a pentacyclic core. The deoxygenated pentacyclic intermediate shows higher cytotoxicity against HeLa and U937 cell lines than isodaphlongamine H, and might become a lead compound for further biological study.