Bioactive sugar

Fig. 1.14 (A) Single-wall carbon nanotubes wrapped by glyco-conjugate polymer with bioactive sugars. (B) Modification of carboxyl-functionalized single-walled carbon nanotubes with biocompatible, water-soluble phosphorylcholine and sugar-based polymers. (A) adapted from [195] with permission from Elsevier, and (B) from [35] reproduced by permission of Wiley-VCH.

H. Dohi, S. Kikuchi, S. Kuwahara, T. Sugai, and H. Shinohara, Synthesis and spectroscopic characterization of single-wall carbon nanotubes wrapped by gly-coconjugate polymer with bioactive sugars, Chem. Phys. Lett., 428 (2006) 98-101. 

The Mukaiyama condensation method was also utilized in the synthesis of several antibiotics and related bioactive substances. These syntheses include apramycin, using 4-azido-2,3,6-tri-(P-benzyl-4-deoxy-) -D-glucopyranosyl fluoride (prepared from the corresponding a-D-glucopyranosyl chloride by the AgF method ) avermectin B , using protected sugar derivatives of oleandrosyl fluoride (a-L-Ole-F) and 0-(a-L-01e)-(1 4)-a-L-0le-F (both... 

Pool concentration of a substance that exceeds the threshold - for example megadose vitamin C - or substances that are excreted unchanged because they cannot be metabolised, such as sugar alcohols, or compounds that are not biologically essential, such as carcinogens, bacterial toxins and some minor plant constituents, are also bioavailable (and thus bioactive) in that they have a metabolic impact, even if this is only the stimulation of detoxification processes, or the use of energy for their excretion. 

Several bioactive fractions from pea stem cell wall pectin have been separated. The fractions contained mainly galacturonides inhibited the process of root formation in thin cell-layer explants, while the fractions contained only neutral sugars stimulated this process to different extend. Analysis of the last fractions showed that they mainly consisted of galactan and arabinogalactan fragments. 

Abiotic spoilage is produced by different physical and chemical changes such as hydrolytic action of enzymes, oxidation of fats, breakdown of proteins, and a browning reaction between proteins and sugars. However, in this chapter we focus on microbial deterioration and their effects on bioactive compounds. 

Another interesting example of the application of sugars in the synthesis of bioactive compounds was presented by Nicotra s group.61 In this approach fructose was used as the starting material for the preparation of a series of GABA ligands, having a considerable therapeutic potential (Fig. 45). 

The bioactivity of imino sugars is due to the fact that they inhibit glycosidases. Once protonated, the imino sugar mime the oxonium ion intermediate of the reaction catalysed by those enzymes (Fig. 32), and therefore binds the active site. 

Virustatic antimetabolites are false DNA building blocks (B) or nucleosides. A nucleoside (e.g., thymidine) consists of a nucleobase (e.g., thymine) and the sugar deoxyribose. In antimetabolites, one of the components is defective. In the body, the abnormal nucleosides undergo bioactivation by attachment of three phosphate residues (p.287). 

Some bioactive compounds contain unusual pentoses in their molecules. This is the case of the antibiotic avilamycin, which contain a L-xylose. Quite recently Bechthold ct al. have biochemically characterized the genesis of this sugar and they have shown that enzyme AviE2 converted UDP-glucuronic acid to UDP-xylose via decarboxylation, indicating that the pentose residue of avilamycin A is derived from D-glucose and not from D-ribose [28]. 

Sugar-derived a,(3-unsaturated lactones are relevant motifs considering their ability to act as functionalized substrates for a variety of transformations. Some of them are bioactive [218-222]. An early synthesis of the enantiomer of (+)-altholactone, a natural product with cytotoxic and antitumor activities (for a review on the bioactivity of styryUactones see [223, 224]), involves the preparation of a furanose-fused a,p-unsaturated 8-lactone intermediate 189 [225]. Starting from a a-D-xy/o-pentodialdofuranose derivative 187, aReformatsky reaction with ethyl bromoacetate introduces the carboxyhc side chain necessary for intramolecular lactonization (Scheme 46). 

---