Formal Synthesis of (±)-Tetrodotoxin via the Oxidative Amidation of a Phenol: On the Structure of the Sato Lactone

A concise synthesis of tetrodotoxin

Tetrodotoxin (TTX) is a neurotoxic natural product that is an indispensable probe in neuroscience, a biosynthetic and ecological enigma, and a celebrated target of synthetic chemistry. Here, we present a stereoselective synthesis of TTX that proceeds in 22 steps from a glucose derivative. The central cyclohexane ring of TTX and its α-tertiary amine moiety were established by the intramolecular 1,3-dipolar cycloaddition of a nitrile oxide, followed by alkynyl addition to the resultant isoxazoline. A ruthenium-catalyzed hydroxylactonization set the stage for the formation of the dioxa-adamantane core. Installation of the guanidine, oxidation of a primary alcohol, and a late-stage epimerization gave a mixture of TTX and anhydro-TTX. This synthetic approach could give ready access to biologically active derivatives.

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

An Oxidative Dearomatization Approach to Tetrodotoxin via a Masked ortho-Benzoquinone

Progress toward a stereoselective synthesis of tetrodotoxin (TTX) is presented. Oxidative dearomatization of a tetrasubstituted guaiacol arene yielded a masked ortho-benzoquinone that intercepted an acyl nitroso species generated in situ by the copper-catalyzed aerobic oxidation of an acyl hydroxylamine. The subsequent alkene dihydroxylation and reduction of a bis-neopentylic ketone proceeded with perfect diastereoselectivity to reveal advanced intermediates toward the synthesis of TTX.

Application of marine natural products in drug research

New diseases are emerging as the environment changes, so drug manufacturers are always on the lookout for new resources to develop effective and safe drugs. In recent years, many bioactive substances have been produced in the marine environment, which represents an alternative resource for new drugs used to combat major diseases such as cancer or inflammation. Many marine-derived medicinal substances are in preclinical or early stage of clinical development, and some marine drugs have been put on the market, such as ET743 (Yondelis®). This review presents the sources, activities, mechanisms of action and syntheses of bioactive substances based on marine natural products in clinical trials and on the market, which is helpful to understand the progress of drug research by application of marine natural products.

Total Synthesis of Pentacyclic (-)-Ambiguine P Using Sequential Indole Functionalizations

The first synthesis of a pentacyclic ambiguine (ambiguine P) is reported. The synthesis takes advantage of sequential alkylations of an indole core to rapidly construct the pentacyclic framework of the natural product. Key to the success of the synthesis was the use of a Nicholas reaction to alkylate at C2, crafting a fused seven-membered ring that is characteristic of the pentacyclic ambiguines, as well as the use of an amide-directed functionalization at C12 to set a requisite quaternary center. A versatile late-stage intermediate was prepared that may be applicable to the synthesis of the other pentacyclic ambiguines.