Editorial [Bioorganic Chemistry Guest Editor: Harri Lonnberg]

The current issue is Part I of the annual thematic issue of Bioorganic Chemistry. Four extensive review articles are included, which offer a nice example of the width of this field. Transformation reactions of nucleosides, structural chemistry of secondary metabolites, synthesis of potentially chemotherapeutic oligonucleotides and methods for construction of conjugates of biopolymers are discussed. While these articles are of considerable general interest, they at the same time constitute a compilation of literature useful both for specialists working in these fields. The first contribution, written by Prof Defrancq and his co-workers, deals with synthesis of oligonucleotide conjugates. Such conjugates have received increasing interest in chemotherapy, in in vitro diagnostics and in in vivo imaging. This review offers an up-to-date survey of the methods exploited in tethering a variety of conjugate groups, ranging from peptides and sugars to fluorescent dyes and nanoparticles, to oligonucleotides. In addition, alternative approaches for immobilization of oligonucleotides to microarrays are described. The second review by Gaynor and Cosstick is a summary of the studies that have led to successful solid-phase synthesis of oligonucleotides having either the 3'- or 5'-bridging oxygen of the internucleosidic phosphodiester linkages replaced with sulfur. The effect of these modifications on the physico-chemical properties of nucleic acids, such as structure and chemical and enzymatic stability, has been summarized and the exploitation of the 3'-S-linkages in mechanistic studies of catalytic nucleic acids discussed. The third paper is a comprehensive review of the transglycosylation reactions of nucleosides by Prof Boryski. These reactions are of great importance, since structurally modified nucleosides are increasingly studied as potential antivirals and as consituents of therapeutic oligonucleotides. As far as sugar-modified nucleosides are concerned, exchange of the base moiety offers a shortcut for the preparation of all four modified nucleosides. Finally, Gademann and Portmann present an overview of the natural products from cyanobacteria, highlighting several classes of secondary metabolites. Some of these metabolites show promise in cancer therapy, some are extremely efficient chelators of iron and some are inhibitors of proteases. In other words, cyanobacteria secondary metabolites constitute a versatile source both for leads of drugs. I thank all the authors for their thorough work and hope that many organic chemists enjoy reading this issue.