Current Organic Synthesis - Volume 3, Issue 4, 2006

There has been significant progress in application of pyranoses and related compounds towards drug discovery and development. This review focuses on strategies for grafting of pharmacophore groups at selected positions on pyranoside and related iminosugar scaffolds. Recent developments in the solid phase synthesis of prospecting combinatorial libraries, syntheses of pyranose based sugar amino acids (SAAs) and other scaffolding for peptidomimetics are included. Although no drug molecule has been developed a number of novel potent ligands for receptors have been identified. It has been shown that these pyranoside derivatives could have improved cellular permeability over peptides. Progress in this area is continually dependant on advances in synthetic carbohydrate chemistry both in solution and on solid phase. These include the development of orthogonal protecting group strategies, strategies for regioselective manipulation of pyranoside hydroxyl groups and strategies that could take increasing advantage of chemoselective reactions. In addition a greater understanding of structural carbohydrate chemistry and the preferred orientations of groups attached to pyranose scaffolds may facilitate synthesis of more potent ligands for receptors.

This review provides a comprehensive survey of the recent progress in the various preparative methods and the application as catalyst of the thiourea and selenourea, their application in the preparation of heterocycles and their biological significances.

This review will present recent achievements in the use of novel reactants and synthetic procedures for the transformation of substrates into epoxide derivatives. This will include both classical chemical methods using novel catalysts and/or cleaner methodologies, and enzymatic preparations using enzymes or cells. Special attention is paid to the preparation of chiral compounds. A comparison of the advantages and disadvantages of the different preparations is also included.

Indoles are extremely important and basic skeletons in many biologically active natural products with specific structures. The development of effective methods for the construction of the indole moiety is one of the most important aims that synthetic chemistry has pursued. Over the past decade, palladium-catalyzed indole synthesis is arguably one of the most successful and straight forward methods for the construction of the pyrrole ring in indole because it offers an efficient entryway from relatively simple precursors with fewer steps, to highly functionalized indoles. This review will summarize recent advances in utilizing this method in the synthesis of most complex indole derivatives such as indolo[2,3-a]carbazoles, optically active 7- methoxytryptophan ethyl esters, pyrimido[4,5-b]indoles and spiro-oxindoles which are present in several biologically important molecules. Also, the use of solid phase chemistry in preparing small libraries of indoles such as two- or three-point diversified complex indole derivatives has been discussed.

The rhodium(II)-carbenoid mediated transformation of diazocarbonyl compounds is well recognized as a useful process for the facile formation of carbon-carbon and carbon-heteroatom bonds under mild reaction conditions. In this review, the incorporation of rhodium(II)-carbenoid transformations in the synthetic planning and the eventual application of rhodium(II) carbenoid reactions in the synthesis of natural products, non-natural compounds of medicinal importance, and advanced intermediates are discussed. Focus is placed on the use of intermolecular and intramolecular C-H and X-H insertion, intermolecular and intramolecular cyclopropanation, and tandem ylide (carbonyl, ammonium, oxonium, sulfonium) formation/1,3-dipolar cycloaddition, [2,3]-sigmatropic or Stevens [1,2]-rearrangement reactions as key step(s) in the synthetic routes.