Total synthesis of dipiperamide A and revision of stereochemical assignment

A General Synthetic Strategy toward the Truxillate Natural Products via Solid-State Photocycloadditions

The truxillates constitute a large class of dimeric natural products featuring a central, highly substituted cyclobutane core. In principle, these structures could be efficiently synthesized via [2 + 2] photocycloaddition. However, the difficulty in controlling the high-energy electronically excited reactive intermediates in the solution state can lead to poor regio- and diastereocontrol. This has limited the use of photocycloaddition methodology toward the synthesis of this important class of natural products. Herein, we demonstrate that acid-controlled precipitation of C-acyl imidazoles promotes a highly selective solid-state photocycloaddition, and the products of this reaction can be quickly transformed into truxillate natural products.

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

Advancing the Logic of Chemical Synthesis: C-H Activation as Strategic and Tactical Disconnections for C-C Bond Construction

The design of synthetic routes by retrosynthetic logic is decisively influenced by the transformations available. Transition-metal-catalyzed C-H activation has emerged as a powerful strategy for C-C bond formation, with myriad methods developed for diverse substrates and coupling partners. However, its uptake in total synthesis has been tepid, partially due to their apparent synthetic intractability, as well as a lack of comprehensive guidelines for implementation. This Review addresses these issues and offers a guide to identify retrosynthetic opportunities to generate C-C bonds by C-H activation processes. By comparing total syntheses accomplished using traditional approaches and recent C-H activation methods, this Review demonstrates how C-H activation enabled C-C bond construction has led to more efficient retrosynthetic strategies, as well as the execution of previously unattainable tactical maneuvers. Finally, shortcomings of existing processes are highlighted; this Review illustrates how some highlighted total syntheses can be further economized by adopting next-generation ligand-enabled approaches.

Alkamides from Piper nigrum L. and Their Inhibitory Activity against Human Liver Microsomal Cytochrome P450 2D6 (CYP2D6)

Drug–herb interaction through inhibition of cytochrome P450 alters the pharmacological response and/or toxicities of drug used concomitantly. In our screening, Piper nigrum L. was observed to inhibit cytochrome P450 2D6 (CYP2D6) in human liver microsomes. Thus, the MeOH extract of this plant was investigated for their chemical constituents and 19 alkamides including a new pipercyclobutanamide were isolated. Their structures were elucidated on the basis of spectroscopic analyses. The isolated compounds were tested for their inhibition on human liver microsomal dextromethorphan O-demethylation activity, a selective marker for CYP2D6, and pipercyclobutanamide A (17) showed the most potent inhibition with an IC50 value of 0.34 μM. The result demonstrated the potential of drug–alkamides interaction on concomitant consume of white pepper with the drugs being metabolized by CYP2D6.

Applications of C-H functionalization logic to cyclobutane synthesis

The application of C-H functionalization logic to target-oriented synthesis provides an exciting new venue for the development of new and useful strategies in organic chemistry. In this article, C-H functionalization reactions are explored as an alternative approach to access pseudodimeric cyclobutane natural products, such as the dictazole and the piperarborenine families. The use of these strategies in a variety of complex settings highlights the subtle geometric, steric, and electronic effects at play in the auxiliary guided C-H functionalization of cyclobutanes.

Stereoselective preparation of cyclobutanes with four different substituents: total synthesis and structural revision of pipercyclobutanamide A and piperchabamide G

A general strategy was developed for the diastereo- and enantioselective synthesis of cyclobutanes with four different substituents. It consists of three transition metal-catalyzed reactions — a RhII-catalyzed cyclopropanation, a AgI-catalyzed regioselective and stereospecific ring expansion, and a RhI-catalyzed addition reaction. Structures of pipercyclobutanamide A and piperchabamide G were synthesized and revised.

Total synthesis and structural revision of the piperarborenines via sequential cyclobutane C-H arylation

A strategy for the construction of unsymmetrical cyclobutanes using C-H functionalization logic is demonstrated in the total synthesis of piperarborenine B and piperarborenine D (reported structure). These syntheses feature a new preparation of cis-cyclobutane dicarboxylates from commercially available coumalate starting materials and a divergent approach to the controlled cis or trans installation of the two distinct aryl rings found in the natural products using the first example of cyclobutane C-H arylation. The structure of piperarborenine D is reassigned to a head-to-head dimer, which was synthesized using an intramolecular [2+2] photocycloaddition strategy.

Development of New Synthetic Methods and Its Application to Total Synthesis of Nitrogen-Containing Bioactive Natural Products

A group of naturally occurring substances containing nitrogen is widely distributed in plants as well as in fungi, animal, marine organisms, and insects, and many exhibit significant biological activity. These natural products with a huge variety of chemical structures include antibiotics, antitumor agents, immunostimulants, drugs affecting the cardiovascular and central nervous systems, analgesics etc. The diverse activities and low natural abundance of this group of natural products when coupled with their molecular complexity warrant development of new and efficient synthetic methods and strategy for the total synthesis of these products, in particular alkaloids. The purpose of this review is to describe some of our achievements in the total synthesis of the naturally-occurring bases including the Dendrobatid alkaloids pumiliotoxin B and allopumiliotoxin A, the anitibiotic streptazolin, the tricyclic marine alkaloids isolated from the ascidians such as fasicularin, lepadiformine, and cylindricine C, and the dimeric monoterpene alkaloid incarvillateine as well as the formal total synthesis of the spirocyclic marine alkaloids halichlorine and pinnaic acid, which are isolated from the Japanese marine sponge and the Okinawan bivalve, respectively.