Structural Revision and Total Synthesis of Azaspiracid-1, Part 1: Intelligence Gathering and Tentative Proposal

The impact of the Mukaiyama aldol reaction in total synthesis

Four decades since Mukaiyama's first reports on the successful application of silicon and boron enolates in directed aldol reactions, the ability of this highly controlled carbon-carbon bond-forming method to simultaneously define stereochemistry, introduce complexity, and construct the carbon skeleton with a characteristic 1,3-oxygenation pattern has made it a powerful tool for natural product synthesis. This Minireview highlights a number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction and discusses the underlying mechanistic rationale that determines the stereochemical outcomes.

Monoclonal antibodies with orthogonal azaspiracid epitopes

Azaspiracid antibodies: Immunization of azaspiracid immunoconjugates has elicited monoclonal antibodies with distinct epitopes on the marine toxin; this will open the way toward azaspiracid diagnostics and the detection of contaminated shellfish before they can enter the food supply.

Chasing molecules that were never there: misassigned natural products and the role of chemical synthesis in modern structure elucidation

Over the course of the past half century, the structural elucidation of unknown natural products has undergone a tremendous revolution. Before World War II, a chemist would have relied almost exclusively on the art of chemical synthesis, primarily in the form of degradation and derivatization reactions, to develop and test structural hypotheses in a process that often took years to complete when grams of material were available. Today, a battery of advanced spectroscopic methods, such as multidimensional NMR spectroscopy and high-resolution mass spectrometry, not to mention X-ray crystallography, exist for the expeditious assignment of structures to highly complex molecules isolated from nature in milligram or sub-milligram quantities. In fact, it could be argued that the characterization of natural products has become a routine task, one which no longer even requires a reaction flask! This Review makes the case that imaginative detective work and chemical synthesis still have important roles to play in the process of solving nature's most intriguing molecular puzzles.

Cascade Reactions in Total Synthesis

The design and implementation of cascade reactions is a challenging facet of organic chemistry, yet one that can impart striking novelty, elegance, and efficiency to synthetic strategies. The application of cascade reactions to natural products synthesis represents a particularly demanding task, but the results can be both stunning and instructive. This Review highlights selected examples of cascade reactions in total synthesis, with particular emphasis on recent applications therein. The examples discussed herein illustrate the power of these processes in the construction of complex molecules and underscore their future potential in chemical synthesis.

Palladium-catalyzed cross-coupling reactions in total synthesis

In studying the evolution of organic chemistry and grasping its essence, one comes quickly to the conclusion that no other type of reaction plays as large a role in shaping this domain of science than carbon-carbon bond-forming reactions. The Grignard, Diels-Alder, and Wittig reactions are but three prominent examples of such processes, and are among those which have undeniably exercised decisive roles in the last century in the emergence of chemical synthesis as we know it today. In the last quarter of the 20th century, a new family of carbon-carbon bond-forming reactions based on transition-metal catalysts evolved as powerful tools in synthesis. Among them, the palladium-catalyzed cross-coupling reactions are the most prominent. In this Review, highlights of a number of selected syntheses are discussed. The examples chosen demonstrate the enormous power of these processes in the art of total synthesis and underscore their future potential in chemical synthesis.

Metathesis reactions in total synthesis

With the exception of palladium-catalyzed cross-couplings, no other group of reactions has had such a profound impact on the formation of carbon-carbon bonds and the art of total synthesis in the last quarter of a century than the metathesis reactions of olefins, enynes, and alkynes. Herein, we highlight a number of selected examples of total syntheses in which such processes played a crucial role and which imparted to these endeavors certain elements of novelty, elegance, and efficiency. Judging from their short but impressive history, the influence of these reactions in chemical synthesis is destined to increase.

Second-Generation Total Synthesis of Azaspiracids-1, -2, and -3

The naturally occurring but scarce marine neurotoxins azaspiracids-1, -2, and -3 have been synthesized from five key building blocks by a convergent strategy that involved dithiane and Stille coupling reactions. The ABCD fragments were constructed through a cascade reaction involving deprotection/self-assembly of the precursors, while the FGHI fragment was forged by a neodymium triflate-induced cyclization. The final ring closure (ring G) was achieved, after the union of all fragments, through an iodoetherification reaction followed by reductive removal of the facilitating iodine residue. These improved, second-generation routes confirm the absolute structures and render all three azaspiracids readily available for biological studies.