Current Organic Chemistry - Volume 7, Issue 5, 2003

This article (the first of three parts) reviews the use of 1,3-dipolar cycloaddition reactions of nitrile oxides and nitronates in the construction of carbohydrate mimics. Preparation of isoxazolidine and other modified nucleosides, isoxazolidine fused systems, C-disaccharides, polyhydroxylated and aminopolyhydroxylated carbocycles and azasugars, amino sugars, polyhydroxylated alkaloids of the pyrrolidine and indolizidine series is described. It is organized depending on the dipole employed and subdivided into separate sections according to the inter- or intramolecular fashion applied and the nature of dipolarophiles and dipoles incorporated. It is mainly dedicated to the synthetic preparations and stereoselectivities observed with limited reports to biological tests and results.

The specific recognition of any given DNA sequence by ligands is expected to revolutionize medicine and biotechnology in the future. Using oligonucleotides as sequence-specific ligands to form triple helical structures offers a particularly attractive approach due to their availability and their simple recognition code based mainly on directional hydrogen bond contacts. However, the recognition code is limited to only two out of four Watson-Crick base pairs in DNA and only homopurine sequences can be effectively targeted by triplex-forming oligonucleotides at present. In order to overcome this limitation much effort has been directed in the past to the development of novel nucleoside analogs capable of binding any given base pair. This review will summarize the different structural approaches to achieve mixed base pair recognition and try to evaluate the various contributions to binding.

Higher 3-deoxy-2-ulosonic acids are a family of widely distributed natural high carbon carbohydrates, of which 3-deoxy-Δ-arabino-hept-2-ulosonic acid (DAH), 3-deoxy-Δ-manno-oct-2-ulosonic acid (KDO, 2), 3-Deoxy-Δ-glycero-Δ-galacto-non-2-ulosonic acid (KDN) and 5-acetamido-3,5-dideoxy-Dglecero- Δ-galacto-non-2-ulosonic acid (N-acetylneuraminic acid) are the most common members. These sugars have been demonstrated to play vital roles in a series of biochemical and biological processes.The family of ulosonic acids has provided potential therapeutic leads in developing inhibitors of corresponding enzymes. Zanamivir (5) is a transition state analogue of 2,3-didehydro-2-deoxy-Nacetylneuraminic acid (Neu5Ac2en), which exhibits high inhibitory activity to influenza neuraminidase (NA) and has been approved for the treatment of influenza. Therefore, the syntheses of these ulosonic acids themselves and their analogs have attracted considerable interest in recent years, and become a current research topic. Herewith the recent progresses in the synthesis of these ulosonic acids and their derivatives are reviewed.

Phosphines play an important role in organometallic chemistry, homogeneous catalysis and synthetic chemistry. Traditionally, phosphines are mainly prepared by one of the following methods: reaction of halophosphines with organometallic reagents, reaction of phosphides with halides, addition of RR'PH to C-C multiple bonds, Friedel-Crafts reactions and reduction of phosphine oxides. In the past one decade or so, powerful catalytic methods have emerged, allowing a variety of structurally and electronically diverse phosphines to be accessed more easily and efficiently. This review, not attempted to be comprehensive, aims to summarise, and demonstrate the utility of, important catalytic methods that have been employed in the synthesis of phosphines and related organophosphorus compounds. The review focuses on reactions involving hydrophosphination, hydrophosphorylation, P-C coupling, C-C coupling and olefin metathesis.