Mini-Reviews in Organic Chemistry - Volume 7, Issue 1, 2010

Since the rediscovery of proline as a catalyst in aldol reaction in 2000 by List, Barbas and Lerner and, soon after, the development of imonium catalysis by D. W. C. MacMillan, the emergence of Organocatalysis as an important instrument in Organic Synthesis is outstanding. Nowadays, one of the most important goals for chemist is the quest for new and more efficient catalysts. One emerging tool for improving existent organocatalysts consists in using additives which interact with the catalysts via supramolecular interactions such as hydrogen bonding. These interactions provide better catalysts in terms of activity and selectivity. The present review aims to cover and discuss the current evolution of this fast growing field.

Catalytic enantioselective addition of organozinc reagents to carbonyl groups is a valuable method for the synthesis of optically active alcohols. Such asymmetric organozinc additions allow the synthesis of chiral alcohols ubiquitous in the structures of natural and manmade compounds. Recent interest in green chemistry has led to active research in the immobilization of catalysts, and their application to asymmetric reactions. Besides simplifying compound separation and recycling, immobilized catalysts offer easier handling of toxic reagents, and convenient operation in continuous flow reactors. Thus, industrial applications of even expensive and complex chiral catalysts can be achieved in an economical and environmentally benign way.

The syntheses and structures of new classes of unsaturated five-membered heterocycles containing selenium or tellurium and silicon or germanium in the rings prepared on the basis of new heterocyclization reactions of selenium dihalides and tetrahalides or tellurium tetrachloride with the bridged diacetylenes are described. The mechanism of the heterocyclization is discussed.

Nucleoside phosphoramidates have recently received considerable interest as pro-drugs of antiviral analogs of nucleoside monophosphates and as constituents of antisense oligonucleotides. For these reasons, the hydrolytic stability of phosphoramidate linkages also is of interest. The present paper gives a survey of the kinetic and mechanistic studies with phosphoramidates, above all the studies with nucleoside phosphoramidates.

The development of the concepts for “Green Chemistry” and the main principles of this field are reviewed. Examples of the application of these principles in different areas of chemistry are included. The frequently used alternative solvents (green solvents – water, PEG, perfluorinated solvents, supercritical liquids) in preparative organic chemistry are described. The present and the future developments of green chemistry in education and organic chemical technology are considered.

The plant cell wall represents a vast carbon source for the induction of carbohydrate-degrading enzymes. The matrix of polysaccharides presents a great structural diversity, containing different sugar residues with the same or different bonds, branched to varying degrees and whose conformation may be like a straight ribbon, a twisted ribbon, an open helix or completely disordered. Cellulose and hemicellulose are the most abundant polysaccharides, accounting for as much as 35-50% and 25-30% of the dry weight of plant cell wall, respectively. The exploitation of plant cell wall polysaccharides requires an arsenal of enzymes with different mode of action. Enzymatic saccharification of plant cell wall components has potential applications in different fields, including fuel, solid waste disposal, animal feed, and paper/textile industry. The present review covers some aspects of plant cell structure and function, having in mind its potential as an inductor of enzyme systems with biotechnology applications.

The polysaccharide alginate is a linear chain binary copolymer made of guluronic acid and mannuronic acid subunits. Alginate is a natural polymer material produced by a number of organisms, including brown algae and bacteria. It has found application in a variety of areas, including food, cosmetics, pharmaceutical and biomedical industries. In recent years, a number of studies have been published on covalent modification of alginate, often through carbodiimide-mediated reactions at the carboxyl moieties. These modifications have imparted a wide range of different chemical and physical material properties, including altered reactivity, hydrophilicity, viscosity and sorption characteristics. This mini-review focuses on the methods and applications of organically modified alginates from recent publications.

Pyrrolo[1,4]benzodiazepines (PBDs) are a growing group of microbial secondary metabolites that showed remarkable biological activities particularly against tumor cells. Their antitumor activity is mainly due to their specifically binding to DNA and other polydeoxynucleotides to form irreversibly polymer-bound drugs. Consequently, they have been the target of several syntheses as well as screening of natural sources to discover new members. This review provides an update on recent discoveries of PBDs as well as a compilation of spectroscopic data described in the literature.

Isomannide, 1,4:3,6-dianhydro-D-mannitol, is a commercially available chiral carbohydrate derived from ready dehydration of naturally occurring D-mannitol. This compound and its derivatives have been widely used in many areas such as building blocks for polymers synthesis, pharmaceutically important compounds, catalysts in asymmetric synthesis, chiral auxiliaries, and recently, in the synthesis of ionic liquids. In this review we show examples of these applications of isomannide and derivatives.