Bioinspired Total Synthesis of (+)-Euphorikanin A

Total Synthesis of Pallamolides A-E

We have achieved the first total synthesis of pallamolides A-E. Of these compounds, pallamolides B-E possess intriguing tetracyclic skeletons with novel intramolecular transesterifications. Key transformations include highly diastereoselective sequential Michael addition reactions to construct the bicyclo[2.2.2]octane core with the simultaneous generation of two quaternary carbon centers, a one-pot SmI2-mediated intramolecular ketyl-enoate cyclization/ketone reduction to generate the key oxabicyclo[3.3.1]nonane moiety, and an acid-mediated deprotection/oxa-Michael addition/β-hydroxy elimination cascade sequence to assemble the tetracyclic pallamolide skeleton. Kinetic resolution of ketone 14 through Corey-Bakshi-Shibata reduction enabled the asymmetric synthesis of pallamolides A-E.

Isolation of Paraphaeoketones: A Plausible Biosynthetic Explanation for Paraphaeolactones via a Benzilic Acid Rearrangement Rather than a Favorskii Rearrangement

Paraphaeoketones A-C (1-3) were isolated from the culture broth of Paraphaeosphaeria sp. KT4192. Their structures and relative configurations were determined using spectroscopic analysis and verified through density functional theory (DFT)-based chemical shift calculations. The absolute configurations of these compounds were determined by comparing the experimental electronic circular dichroism (ECD) spectra with those based on DFT calculations. We also propose a plausible biosynthetic route to 1-3. While our prior studies on the isolation and structural elucidation of paraphaeolactones (e.g., 4) led us to suggest a Favorskii rearrangement for their biosynthesis, the isolation of 2 prompted the proposal of an alternative biosynthesis for 4, featuring a benzilic acid rearrangement of 2. Moreover, an in vitro conversion of 2 into 4 was achieved successfully, suggesting that a biosynthetic pathway for paraphaeolactones involving a benzilic acid rearrangement is more plausible than the previously presumed Favorskii rearrangement pathway. Arguments based on DFT calculations for these pathways are also described.

Survey of natural products reported by Asian research groups in 2022

The new natural products reported in 2022 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2022 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Bioinspired Total Synthesis of Bipolarolides A and B

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium-halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring-closing metathesis reactions to assemble the five- and eight-membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton.

Total Synthesis of (+)-Euphorikanin A via an Atropospecific Cascade

A total synthesis of the ingenane-derived diterpenoid (+)-euphorikanin A is described. Key to the strategy is a stereocontrolled one-pot sequence consisting of transannular aldol addition reaction, hemiketal formation, and subsequent semipinacol rearrangement that efficiently leads to the complete euphorikanin skeleton. Atroposelective ring-closing olefin metathesis proved critical for the stereospecific cascade, leading to formation of a (Z)-bicyclo[7.4.1]tetradecenone core. An additional salient feature of the route is pyrolysis of a bis-methylxanthate to cleanly furnish the natural product.

Recent advancements in the use of Bobbitt's salt and 4-acetamidoTEMPO

Recent advances in synthetic methodologies for selective, oxidative transformations using Bobbitt's salt (4-acetamido-2,2,6,6-tetramethyl-1-oxopiperidinium tetrafluoroborate, 1) and its stable organic nitroxide counterpart ACT (4-acetamidoTEMPO, 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxyl, 2) have led to increased applications across a broad array of disciplines. Current applications and mechanistic understanding of these metal-free, environmentally benign, and easily accessible organic oxidants now span well-beyond the seminal use of 1 and 2 in selective alcohol oxidations. New synthetic methodologies for the oxidation of alcohols, ethers, amines, thiols, C-H bonds and other functional groups with 1 and 2 along with the field's current mechanistic understandings of these processes are presented alongside our contributions in this area. Exciting new areas harnessing the unique properties of these oxidants include: applications to drug discovery and natural product total synthesis, the development of new electrocatalytic methods for depolymerization of lignin and modification of other biopolymers, in vitro and in vivo nucleoside modifications, applications in supramolecular catalysis, the synthesis of new polymers and materials, enhancements in the design of organic redox flow batteries, uses in organic fuel cells, applications and advancements in energy storage, the development of electrochemical sensors, and the production of renewable fuels.

Bioinspired Synthesis of Spirochensilide A from Lanosterol

A bioinspired synthesis of spirochensilide A from commercially available lanosterol is reported. The synthesis features a directed C-H oxidation, a Wagner-Meerwein-type double methyl migration, a Meinwald rearrangement, and a double-bond isomerization/spiroketal formation cascade. The proposed biosynthetic speculation was modified by this synthetic sequence, which also served as a platform for the synthesis of other lanostanes with migrating methyl groups.