background and overview
Glycosides, also known as glycosides, are a new type of non-ionic surfactant, which is the hemiacetal hydroxyl group of monosaccharide or oligosaccharide and the hydroxyl group, amino group or sulfur hydroxyl group in another molecule to produce hydrate. Therefore, a glycoside can be divided into two parts. One part is the residue of sugar (the sugar removes the hemiacetal hydroxyl group), and the other part is the ligand (non-sugar part), and its bond is called the glycosidic bond. The ligand part can be very simple or complicated. Glycosidic bonds can be connected to each other by oxygen, sulfur, and nitrogen atoms. Their glycosides are referred to as O-glycoside, S-glycoside, N-glycoside or C- glycoside. The ligand of glycosides can be sugars, which are condensed into disaccharides, oligosaccharides and polysaccharides. Glycosides are widely distributed in the roots, stems, leaves, flowers and fruits of plants. Most of them are colored crystals, soluble in water. It generally tastes bitter. Some are highly toxic. Sugar and other substances are produced when hydrolyzed. Due to the different stereoconfiguration, glycosides have two types: α and β. Glycosides of glucose (glucoside) and glycosides of other sugars, most of which are β-glycosides.
classification
Glycosides can be classified according to different glycoside atoms, aglycones, and glycoside bonds. It can also be classified according to the carbon structure of the terminal group, the number of monosaccharides and sugar chains at the terminal, and the primary and secondary glycosides existing in the organism.
synthesis
Glycosides are a new type of non-ionic surfactant, which are synthesized from carbohydrates and natural fatty alcohols.
Chemical synthesis of glycosides: This method began in 1893, and so far, its industrial production has mainly used this method. The product obtained by chemical method is generally a mixture of various isomers and by-products (Fischer method). If the product purity is high, it needs to be protected, activated, coupled, and protected.
(Konigs- Knorr method). The catalyst used in the roundabout method is expensive and complex, so the glycoside products are mostly mixtures, and its application is mainly limited to washing products.
Glycosidase catalyzes the synthesis of glycosides: There are two ways to catalyze the glycosidase reaction: the reverse hydrolysis reaction catalyzed by glycosidase; the transglycosylation reaction catalyzed by glycosidase. To successfully apply this pathway to synthesize glycosides and require a high yield, two key points must be paid attention to: transglycosidation must be hydrolyzed faster than glycosides; the hydrolysis rate of the product is slower than that of the sugar-based donor.
Glycosyltransferase catalyzes the synthesis of glycosides: In nature, the synthesis of glycosides mainly depends on the production of glycosyltransferase
With, glycosyltransferase can specifically catalyze the transfer of glycosyl groups from active intermediates (such as UDP derivatives) to target product molecules, with high selectivity and catalytic efficiency. Glycosyltransferase is only responsible for the transfer of glycosyl groups, and does not cause the hydrolysis of the substrate or product. It can be said to be an ideal catalyst. This method needs to complete a two-step substitution reaction, first to produce a glycosyl-enzyme intermediate complex, and then the receptor completes the second step of substitution reaction. The application of this method is costly and difficult, and it is difficult to carry out industrial production in the enzymatic synthesis of glycoside compounds
Glycoside synthase catalyzes the synthesis of glycosides: Glycoside synthase can use different donors to specifically catalyze the synthesis of glycosidic bonds. This method mainly refers to the synthesis of oligosaccharides. The catalytic pathway of glycoside synthase is divided into two ways: flip and hold (Figure 2). In the flip-type glycoside synthase, the glycoside fluoride containing the α-glycoside bond is used as an analog of the glycoside intermediate. In the retention-type glycoside synthase, the substrate is activated β-glycoside, which is activated by the enzyme. Under the action, glycosidic acid is formed as an intermediate. In the subsequent deglycosylation step, both are identical glycosyl groups transferred to the receptor (R) to produce oligosaccharides. This method not only has stereoselectivity and regioselectivity, but also has high efficiency, short time and cheap substrate, so it is a new choice for the industrial production of oligosaccharides.
Glycoside synthase catalyzed synthesis pathway
Whole-cell catalytic synthesis of glycosides: The essence of whole-cell catalytic synthesis of glycosides is the transglycosylation catalyzed by glycosidase or glycosyltransferase in the cell. Whole cell-catalyzed synthesis has been widely used to prepare chiral drugs and biologically active compounds. Biological cells are used as biocatalysts after suspension culture and other operations, with oligosaccharides such as maltose as donors, and hydroxyl-containing compounds such as alcohols or phenols as receptors. Under suitable conditions, glycosides are synthesized by transglycosylation. The whole cell catalyzed synthesis of glycosides has the characteristics of mild reaction conditions, fewer steps, higher yield, environmental friendliness, high product purity and easy separation, and low cost than enzyme catalysis. It has important application value in glycoside synthesis.
application-tobacco
glycosides are important latent aroma substances in tobacco. the aroma components in tobacco are divided into free state and glycoside binding state [4]. Most of the glycosides isolated and identified from tobacco leaves are bloomol A, 3-hydroxy-5, 6-epoxy-ionol, 5, 6-β-ionol 2 hydrogen, deflavolide, 3-oxo-ɑionol, benzyl alcohol, 3-hydroxymacromatone, 4-hydroxy-β-ionol and 2, 6-Dimethoxy-4-vinylphenol and other glycosides [5]. Glycosides have made great contributions to improving tobacco flavor and enhancing the comfort of flavor. It can be directly added to cigarettes as a fragrance to eliminate some unstable compounds that affect the quality of the fragrance, make the fragrance more comfortable and coordinated, avoid the loss of fragrance caused by the direct addition of the fragrance enhancer, and destroy the natural fragrance of tobacco.