Current Organic Chemistry - Volume 7, Issue 16, 2003

The synthesis of vitamin K and its analogues has been an important goal since the biochemical roles of the K vitamins were elucidated. This review presents a detailed account of syntheses of natural K vitamins and analogues that contain side chain functionality.

Phytoalexins are induced chemical defenses produced by plants in response to diverse forms of stress, including microbial attack. Although phytoalexins from over 30 different plant families have been isolated since Müller first proposed this term in 1940, crucifers were the first plants reported to produce phytoalexins containing sulfur and nitrogen. Most of the cruciferous phytoalexins are biogenetically derived from tryptophan but have rather different chemical structures as well as biological activities. The relatively large amounts of phytoalexins currently required for a diversity of chemical and biological studies are usually obtainable through synthesis, as isolation from plants is difficult and very time consuming. Herein we review work reporting the chemical structures, syntheses, and biosyntheses of cruciferous phytoalexins and present new perspectives on the potential applications of these compounds and analogs.

The overwhelming majority of unnatural foldamers described so far adopt various helical conformations. Helical foldamers include peptidomimetic oligomers such α-, β- and γ-peptides, and non-biological helices such as helicates, oligoheterocycles and olio(phenylene ethynylenes). Lying between peptidomimetic and non-biological foldamers are oligoarylamides whose backbones are rigidified by strong intramolecular hydrogen bonds. The localized nature of the intramolecular hydrogen bonds allows structure the tuning of both the side chains and the curvature of the backbones, leading to helices of different surface properties and tunable interior cavities. As a result, hollow helices with interior channels of tunable, finite diameters are generated. Thus, unnatural helical foldamers have evolved from providing examples of stably folded secondary structures to demonstrating features of higher structural levels of biomacromolecules, e.g., the creation of nanocavities.

The use of indium salts as catalysts and mediators in addition, cyclization, aromatic electrophilic substitution, nucleophilic substitution, coupling, reduction, rearrangement and polymerization reactions that have appeared in papers published between 2000 and the first half of 2002 is reviewed. InCl3, InBr3, InI3, InCl, InBr, InI, In(OTf)3, and In(NTf)3 are most commonly used indium salts depending on the reaction type and reaction conditions. The use of indium salts, generally, allows the reaction to be carried out under mild conditions, with high yield and high selectivity. Sometimes, an aqueous medium can be used and the catalyst can be reused.

The most recent achievements in the construction of the 1,3-diketone moiety are reviewed. Though both classical and modern approaches to the synthesis of 1,3-diketones are compared and analyzed in terms of efficiency, functional group compatibility, regio-, and stereoselectivity, main attention is paid to recently discovered methods based on rearrangements and concerted mechanisms. Molecular structure investigations, appearance in nature, and biological activity of 1,3-diketones are also briefly reviewed.