This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce ∼4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applica...

Anisotropic metal nanoparticles: Synthesis, assembly, and optical applications

http://aether.cmi.ua.ac.be/artikels/Artikels%20Gitte/Artikels/Reviews/Trans.%20Metal.%20catal.%20reactions%20Chem.%20rev.%20042127.pdf

Transition-Metal-Catalyzed Reactions in Heterocyclic Synthesis

Synthesis of oxygen- and nitrogen-containing heterocycles by ring-closing metathesis.

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.

Metathesis Reactions in Total Synthesis

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis

More than 20,000 people suffer annually from ciguatera seafood poisoning in subtropical and tropical regions. The extremely low content of the causative neurotoxins, designated as ciguatoxins, in fish has hampered the isolation, detailed biological studies, and preparation of anti-ciguatoxin antibodies for detecting these toxins. The large (3 nanometers long) and complicated molecular structure of ciguatoxins has impeded chemists from completing their total synthesis. Our highly convergent strategic approach featuring the chemoselective ring-closing metathesis reaction as a key tactic has enabled the total synthesis of ciguatoxin CTX3C, which will provide a practical supply for further studies.

https://science.sciencemag.org/content/sci/294/5548/1904.full.pdf

Total synthesis of ciguatoxin CTX3C

Practical total synthesis of ciguatoxin CTX3C by improved protective group strategy.

More than 20,000 people suffer annually from ciguatera seafood poisoning in subtropical and tropical regions. The extremely low content of the causative neurotoxins, designated as ciguatoxins, in fish has hampered isolation, detailed biological studies, and preparation of anti-ciguatoxin antibodies for detecting these toxins. Furthermore, the large (3 nm in length) and complex molecular structure of ciguatoxins has impeded chemists from completing their total synthesis. In this article, the full details of studies leading to the total synthesis of ciguatoxin CTX3C are provided. The key elements of the first-generation approach include O,O-acetal formation from the right and left wing fragments, conversion from O,O-acetal to O,S-acetal, a radical reaction to cyclize the G ring, a ring-closing metathesis reaction to close the F ring, and final removal of the 2-naphtylmethyl protective groups. Subsequent studies provided a second-generation total synthesis, which is more concise and results in a higher yield. Second-generation synthesis was accomplished by using a direct method of constructing the key intermediate O,S-acetal from α-chlorosulfide and a secondary alcohol. These syntheses ensure a practical supply of ciguatoxin for biological applications.

https://www.pnas.org/content/pnas/101/33/12013.full.pdf

First- and second-generation total synthesis of ciguatoxin CTX3C

Ciguatoxins are the major causative toxins of ciguatera seafood poisoning. Limited availability of ciguatoxins has hampered the development of a reliable and specific immunoassay for detecting these toxins in contaminated fish. Monoclonal antibodies (mAbs) specific against both ends of ciguatoxin CTX3C were prepared by immunization of mice with protein conjugates of rationally designed synthetic haptens, 3 and 4, in place of the natural toxin. Haptenic groups that possess a surface area larger than 400 A(2) were required to produce mAbs that can bind strongly to CTX3C itself. A direct sandwich enzyme-linked immunosorbent assay (ELISA) using these mAbs was established to detect CTX3C at the ppb level with no cross-reactivity against other related marine toxins, including brevetoxin A, brevetoxin B, okadaic acid, or maitotoxin.

Megumi Maruyama

Papers

Total synthesis of ciguatoxin CTX3C

Practical total synthesis of ciguatoxin CTX3C by improved protective group strategy.

First- and second-generation total synthesis of ciguatoxin CTX3C

Synthesis-based approach toward direct sandwich immunoassay for ciguatoxin CTX3C.

Structure of bilobalide, a rare tert-butyl containing sesquiterpenoid related to the C20-ginkgolides