Glycosidation, enzymatic/chemical

At temperatures above Tm, chemical and enzymatic degradation of microbial exopolysaccharides is enhanced. The apparent enhanced stability of microbial exopolysaccharides in their ordered confirmation is thought to be due to the glycosidic bonds in the backbone of the polymer which raises the activation energy. This restricted movement would also restrict access of enzymes and chemicals to the backbone. 

The solubility of iridoids depends on their state (free, glycosylated, acetylated), but usually they are extracted with polar solvents methanol, ethanol, aqueous alcohols, and rarely acetone. Iridoid glycosides are more or less stable some of them are very sensitive to acids and alkalis. Some iridoid glycosides such as aucubin suffer color modification after chemical or enzymatic hydrolysis they give first a blue to green... 

G.C.H. Derksen, M. Naayer, T.A. van Beek, A. Capelle, I.K. Haaksman, H.A. van Doren and JE. Groot, Chemical and enzymatic hydrolysis of anthraquinone glycosides from madder roots, Phytochem. Anal., 14, 137 144 (2003). 

The objectives of the studies reported herein were to (a) compare the effects of a series of phenolic acids, coumarins, and flavonoids on whole chain electron transport and phosphorylation in Isolated plant chloroplasts and mitochondria and (b) identify specific sites of inhibition with polarographic and enzymatic techniques. Exploratory studies were conducted with the 20 compounds listed in Table I. The three glycosides are shown indented below the corresponding aglycones. Detailed studies were conducted with the six compounds, one representative member from each chemical family, designated with an asterisk. 

Glycosides of ergot alkaloids were isolated as naturally occurring products [40] and a large series of them has been prepared by chemical and enzymatic methods [41]. 

The structures of the compounds were elucidated by a combination of NMR techniques (lH-, 13C-, and 13C-DEPT NMR) and chemical transformation, enzymatic degradation, and as well as mass spectrometry, which gives information on the saccharide sequence. A more recent approach consists of an extensive use of high-resolution 2D NMR techniques, such as homonuclear and heteronuclear correlated spectroscopy (DQF-COSY, HOHAHA, HSQC, HMBC) and NOE spectroscopy (NOESY, ROESY), which now play the most important role in the structural elucidation of intact glycosides. These techniques are very sensitive and non destructive and allow easy recovery of the intact compounds for subsequent biological testing. 

J. O. Nagy and M. D. Bednarski, The chemical-enzymatic synthesis of a carbon glycoside of W-acetyl neuraminic acid, Tetrahedron Lett. 32 3953 (1991). 

By simulating evolution in vitro it has become possible to isolate artificial ribozymes from synthetic combinatorial RNA libraries [1, 2]. This approach has great potential for many reasons. First, this strategy enables generation of catalysts that accelerate a variety of chemical reactions, e.g. amide bond formation, N-glycosidic bond formation, or Michael reactions. This combinatorial approach is a powerful tool for catalysis research, because neither prior knowledge of structural prerequisites or reaction mechanisms nor laborious trial-and-error syntheses are necessary (also for non-enzymatic reactions, as discussed in Chapter 5.4). The iterative procedure of in-vitro selection enables handling of up to 1016 different compounds... 

Combined approaches have been developed to overcome problems associated with chemically and enzymatically based methods. In such an approach, glycosidic linkages that are very difficult to introduce chemically are introduced enzymatically and vice versa. The enzymatic approach has proven to be extremely valuable for the introduction of neuramic acid units in a synthetically prepared oligosaccharide. 

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