Total Synthesis of the 7,10-Epimer of the Proposed Structure of Amphidinolide N, Part I: Synthesis of the C1-C13 Subunit

Highly Enantioselective Construction of Multifunctional Silicon-Stereogenic Silacycles by Asymmetric Enamine Catalysis

We report the first highly enantioselective construction of silicon-stereocenters by asymmetric enamine catalysis. An unprecedented desymmetric intramolecular aldolization of prochiral siladials was thus developed for the facile access of multifunctional silicon-stereogenic silacycles in high to excellent enantioselectivity. With an enal moiety, these adducts could be readily elaborated for the diverse synthesis of silicon-stereogenic compounds, and for late-stage modification.

The Tetrahydrofuran Motif in Polyketide Marine Drugs

Oxygen heterocycles are units that are abundant in a great number of marine natural products. Among them, marine polyketides containing tetrahydrofuran rings have attracted great attention within the scientific community due to their challenging structures and promising biological activities. An overview of the most important marine tetrahydrofuran polyketides, with a focused discussion on their isolation, structure determination, approaches to their total synthesis, and biological studies is provided.

Structure and Stereochemistry of Amphidinolide N Congeners from Marine Dinoflagellate Amphidinium Species

Two highly potent cytotoxic 26-membered macrolides, isocaribenolide-I (1) and a chlorohydrin 2, together with known amphidinolide N (3), have been isolated from a free-swimming dinoflagellate Amphidinium species (KCA09053 and KCA09056 strains) collected off Iriomote Island, Japan. The structures of 1 and 2 were determined to be a congener of 3 with an isobutyl terminus and the chlorohydrin form of 3, respectively, by detailed analyses of spectroscopic data. The relative stereochemistries of 1 and 2 were elucidated by the conformational analyses based on NMR data.

Cobalt-Catalyzed Hartung-Mukaiyama Cyclization of γ-Hydroxy Olefins: Stereocontrolled Synthesis of the Tetrahydrofuran Moiety of Amphidinolide N

Cobalt-catalyzed Mukaiyama-type cyclization of γ-hydroxy olefins is known as an atom- and step-economical means for stereoselective synthesis of 2,5-trans-substituted tetrahydrofuran derivatives. In this study, we investigated the synthesis of a series of 2,5-substituted tetrahydrofuran derivatives by means of a cobalt-catalyzed Hartung-Mukaiyama cyclization. The stereochemical consequence of the reaction was found to be largely dependent on the substitution pattern and relative configuration of γ-hydroxy olefins. 2,5-cis-Substituted tetrahydrofuran derivatives could be obtained diastereoselectively from appropriately substituted γ-hydroxy olefins. Additionally, relatively bulky olefin substituents and unprotected hydroxy groups at non-interfering positions (e.g., α and δ) were well tolerated in the reaction. Finally, the synthetic versatility of the Hartung-Mukaiyama cyclization was demonstrated through a stereocontrolled synthesis of the tetrahydrofuran moiety of amphidinolide N, a potent cytotoxic macrolide of marine origin. This study expands the capacity of Mukaiyama-type cyclization in that it can be used in convergent assembly of complex tetrahydrofuran motifs from internal olefins.