Glycosides.pptVIP

Saccharides and Glycosides 3.1 Saccharides ( also called Carbohydrates) 3.1.2 monosaccharides 3.1.3 Stereochemistry of monosaccharides Stereochemical descriptors: D and L notation 3.1.4 polysaccharides 3.2 glycosides 3.2.1 classification of glycosides O-glycoside: 3.3 physical properties 3.4 chemical properties the cleavage of the aglycone-sugar link acid hydrolysis The rule of fission of glycosidic linkage by acid hydrolysis (苷键被酸催化水解的难易规律) The density of electronic cloud and spacial surroundings of the atom of glycosidic linkage play an important role during acid hydrolysis. 4) The bigger the size of C5-group on the pyranoside , the more difficult the acid hydrolysis of the glycosides Question : comparing the speed of hydrolysis Smith Degredation Advantages: suitable for C-glycosides and O –glycosides which its aglycone structure are changed after acid hydrolysis Disadvantages: unsuitable for glycosides which owns 1,2 -dihydroxyl O-glycosides C-glycosides Mechanism is similar to acid hydrolysis. Reagent: acetic anhydride/H2SO4/HClO4 Products: acylated aglycone and acylated sugar alkaline hydrolysis (碱催化水解) Except ester linkage, phenolic glycosides, enol form glycosides and glycosides with ?- electron withdrawing group, the glycosidic linkage is stable in alkaline aqueous solution. 一般苷键对稀碱稳定，但某些特殊的苷酯苷、酚苷、烯醇苷和?-吸电子基取代的苷（这些苷键具有酯的性质），遇碱可水解。 优点: ①获知苷键构型 ②可得到真正的苷元 ③可得到次级苷 characteristic （2）mild reaction condition (反应条件温和) Extraction and Isolation Extraction To extract out original glycosides： destroy enzyme To extract out secondary glycosides: activate enzyme acetolysis The rule of acetolysis of β-diglucosides （from difficult to easy) (1 2) (1 3) (1 4) (1 6) enzymolysis (酶水解) Advantages: ① a way to know the configuration of glycosides ② obtaining the original aglycone ③ obtaining the secondary glycosides (1) a high degree of specif