Carbohydrates ring, 2-amino

These methods have many stages and require preliminary protection of the OH-groups, followed by the removal of protective functions. The advantages of E. Fishers method include its universality - the ability to introduce ureido (thioureido) fragments in any position of the carbohydrate ring with the presence of amino group in this position. 

Another example of the biosynthesis of a thiazole ring is in enzymatic biosynthesis of thiamin. Thiamin is a thiazole-containing vitamin whose supply in humans relies on diet. It acts as a coenzyme and plays an important role in carbohydrate and amino acid metabolism <2003NPR184>. Thiamin deficiency can be fatal. 

Ammonium hydroxide Pyrimidine nucleosides from carbohydrates and cyanoacetylenes via carbohydrate 2-amino-Zl -oxazoline ring... 

The 3-amino group can be easily AT-acylated to give acrylamide or fatty acid esters [110]. Silyation of 3-ketosucrose at the free hydroxyl groups with chlorotrimethyl silane provides a derivative that can be modified by Grignard-type reactions introducing allyl or alkyl chains onto the carbohydrate ring [110] (reaction 4.107). 

Ring B and the central three-carbon bridge forming the C ring (see Fig. 5.1) originate from the amino acid phenylalanine, itself a product of the shikimate pathway, a plastid-based process which generates aromatic amino acids from simple carbohydrate building blocks. Phenylalanine, and to a lesser extent tyrosine, are then fed into flavonoid biosynthesis via phenylpropanoid (C6-C3) metabolism (see Fig. 5.1). 

In carbohydrate chemistry, the most described method for the preparation of saccharidic thionocarbamates involves preliminary introduction of the amine function on a partially or non-protected saccharidic template. The condensation of amino sugars with carbon disulfide or thiophosgene leads to cyclization in 1,3-oxazolidine- or l,3-oxazine-2-thiones. This reaction involves the formation of an intermediate isothiocyanate, which reacts further with a 3- or y-located hydroxyl group. The viability and facility of this process depends on the saccharidic ring size and the inherent strain. Some major rules can be put into light from the cases studied 30... 

The precise chemical interactions between an adhesin and its receptor are also important. For example, direct- and water-mediated hydrogen bonds are the most important interactions within the carbohydrate-recognition domain in carbohydrate-binding adhesins on the host cell surface (Weis and Drickamer, 1996). Nonpolar van der Waals interactions and hydrophobic "stacking of the receptor oligosaccharide rings with aromatic amino acid side chains of the bacterial adhesin protein also contribute to oligosaccharide-protein interactions. X-ray structural... 

While functional (immunological) mimicry has been established, the basis of mimicry on the molecular level remains to be explained. Several hypotheses have been put forward one of the earliest was that the side chains of aromatic amino acid residues might mimic the hydrophobic faces of the pyranosyl rings of carbohydrates. Before 1997, no structural evidence was available to support or discount these hypotheses. The nature of peptide-carbohydrate mimicry on the molecular level became the subject of structural investigations, and the resulting studies along with functional data will be discussed below. 

Alkyl (or acyl) derivatives of the 6-amino-6-deoxy carbohydrates are examples of derivatives in which the hydrophilic and hydrophobic moieties are linked at other positions than C-1. Thus 6-amino-6-deoxy-D-galactose derivatives 34 were prepared from l,2 3,4-di-0-isopropylidene-6-0-tosyl-a-D-galacto-pyranose by the following reactions (1) substitution of the leaving group at C-6 by a phthaloyl function, (2) hydrazinolysis to afford a 6-amino-6-deoxy intermediate, (3) reaction of acyl or sulfonyl chlorides at the amino function, (4) deprotection of the acetal rings to afford the expected glycolipid 34 [56]. 

---