Chapter 24 Carbohydrates and Nucleic Acids Organic Chemistry, 6th Edition L. G. Wade, Jr. Chapter 24 Carbohydrates and Nucleic Acids

Content Introduction Structure and configuration of saccharides Reactions of monosaccharides Disaccharides and polysaccharides

Sec 1 introduction

能源物质、结构物质、信息载体 生物活性物质 肌糖原－能源 昆虫外骨骼－糖 动物干重2％ 韧带－结构糖 细胞表面识别标记－糖 结缔组织－结构糖 糖蛋白、糖脂、信息分子糖 生物活性物质

Carbohydrates Synthesized by plants using sunlight to convert CO2 and H2O to glucose and O2. Polymers include starch and cellulose. Starch is storage unit for solar energy. Most sugars have formula Cn(H2O)n, “hydrate of carbon.”

Classification of Carbohydrates Monosaccharides or simple sugars polyhydroxyaldehydes or aldoses polyhydroxyketones or ketoses Disaccharides can be hydrolyzed to two monosaccharides. Polysaccharides hydrolyze to many monosaccharide units. E.g., starch and cellulose have > 1000 glucose units.

Sugars in Fruits % Sugar of total fruit weight (Fennema, 1985 ) High in fructose; other sugars present also

Sugars in Vegetables 花椰菜 利马豆 % Sugar of total vegetable weight (Fennema, 1985) Vegetables less sweet, higher in sucrose 花椰菜 利马豆

Sugars in Processed Foods % Sugar of total food weight 调味蕃茄酱 果酱

Monosaccharides Classified by: aldose or ketose number of carbons in chain configuration of chiral carbon farthest from the carbonyl group fructose, a D-ketohexose => glucose, a D-aldohexose

Sec 2 Structure and configuration of sacchrides D and L Sugars Cyclization of Monosaccharides Cyclic Structure Haworth Projections Conformational Formulas

Structure and configuration of sacchrides D sugars can be degraded to the dextrorotatory (+) form of glyceraldehyde. L sugars can be degraded to the levorotatory (-) form of glyceraldehyde. D L---编号最大的手性碳决定； 天然存在的糖大多数都是D－型糖

Erythro and Threo 赤式 & 苏式 Terms used for diastereomers with two adjacent chiral C’s, without symmetric ends. For symmetric molecules, use meso or d,l. =>

The D Aldose Family

Cyclization of Monosaccharides 直链氧环式

直链氧环式

Sec 3 Reactions od monosachrides Mutarotation and Epimerization(变旋现象与差向异构化) 显色反应 Oxidation and reduction Formation of Glycosides(成苷反应) Other reactions Ether Formation Ester Formation Osazone Formation

Epimers 差向异构体 Sugars that differ only in their stereochemistry at a single carbon.

1. Mutarotation and Epimerization (变旋现象与差向异构化) 变旋现象（一般水溶液中） -D-(+)-吡喃葡萄糖 -D-(+)-吡喃葡萄糖 mp 146℃,[  ]D25=+112° mp 150 ℃, [  ]D25=+18.7 °

Mutarotation An aqueous solution of D-glucose contains an equilibrium mixture of α-D-glucopyranose, β-D-glycopyranose, and the intermediate open-chain form. Crystallization below 98°C gives the α anomer, and crystallization above 98°C gives the β anomer. 23

Cyclic Structure for Glucose Glucose cyclic hemiacetal formed by reaction of -CHO with -OH on C5. D-glucopyranose

Mutarotation and Epimerization (变旋现象与差向异构化)

Anomers D、L-判别：C编号顺时针转时尾巴上的羟甲基朝上，为D。 、－判别：尾巴上的羟甲基和新生成的OH在环两侧为。

dextrose; dextrorotatory Mutarotation Glucose also called dextrose; dextrorotatory

Sugar Isomers in Water Generally only a few isomers predominate Straight chain form present in very small amounts (< 1%)! (Belitz and Grosch, 1999; © Springer-Verlag) a b

差向异构化

Base-Catalyzed Epimerization of Glucose 差向异构体：在多手性碳化合物中只有一个手性碳构型不同而其它构型均相同的非对映异构体。 Under basic conditions, stereochemistry is lost at the carbon atom next to the carbonyl group. In base, H on C2 may be removed to form enolate ion. Reprotonation may change the stereochemistry of C2. Because a mixture of epimers results, this stereochemical change is called epimerization. 33

Enediol Rearrangement In base, the position of the C=O can shift. Chemists use acidic or neutral solutions of sugars to preserve their identity. =>

2、脱水和显色反应

鉴别糖与非糖 醛糖与酮糖

3. Oxidation and Reduction NaBH4 H2/Ni Oxidation Oxidation by Bromine Oxidation by Nitric Acid Oxidation by HIO4 Oxidation by Tollens Reagent

Reduction of Simple Sugars C=O of aldoses or ketoses can be reduced to C-OH by NaBH4 or H2/Ni. Name the sugar alcohol by adding -itol to the root name of the sugar. Reduction of D-glucose produces D-glucitol, Reduction of D-fructose produces a mixture of D-glucitol and D-mannitol.

Oxidation by Bromine Bromine water oxidizes aldehyde, but not ketone or alcohol; forms aldonic acid.

Oxidation by Nitric Acid Nitric acid oxidizes the aldehyde and the terminal alcohol; forms aldaric acid.

Oxidation by Tollens Reagent Tollens reagent reacts with aldehyde, but the base promotes enediol rearrangements, so ketoses react too. Sugars that give a silver mirror with Tollens are called reducing sugars.

所有的单糖都有还原性；所有的多糖都是无还原性;

Periodic Acid Cleavage Periodic acid cleaves vicinal diols to give two carbonyl compounds. Separation and identification of the products determine the size of the ring.

4. Formation of Glycosides 苷（糖甙键的生成）的形成 甲基-D-(+)-吡喃葡萄糖苷 甲基 -D-(+)-吡喃葡萄糖苷 mp 165℃,[  ]D25=+158° mp 107 ℃, [  ]D25=-33 °

Ether Formation Sugars are difficult to recrystallize from water because of their high solubility. Convert all -OH groups to -OR, using a modified Williamson synthesis, after converting sugar to acetal, stable in base.

Ester Formation Acetic anhydride with pyridine catalyst converts all the oxygens to acetate esters.

Nonreducing Sugars Glycosides are acetals, stable in base, so they do not react with Tollens reagent. Disaccharides and polysaccharides are also acetals, nonreducing sugars.

5. Osazone Formation 成脎反应 Both C1 and C2 react withphenylhydrazine.

Ruff Degradation Aldose chain is shortened by oxidizing the aldehyde to -COOH, then decarboxylation.

Kiliani-Fischer Synthesis This process lengthens the aldose chain. A mixture of C2 epimers is formed.

Fischer’s Proof Emil Fischer determined the configuration around each chiral carbon in D-glucose in 1891, using Ruff degradation and oxidation reactions. He assumed that the -OH is on the right in the Fischer projection for D-glyceraldehyde. This guess turned out to be correct.

Sec 4 Disaccharides and Polysaccharides 二糖与多糖 一个单糖分子的半缩 醛羟基与另一个单糖 分子的羟基（醇羟基或 半缩醛羟基）之间缩 去一分子水的产物 蔗糖 麦芽糖 乳糖 纤维二糖 二糖

Disaccharides Three naturally occurring glycosidic linkages: 1-4’ link: The anomeric carbon is bonded to oxygen on C4 of second sugar. 1-6’ link: The anomeric carbon is bonded to oxygen on C6 of second sugar. 1-1’ link: The anomeric carbons of the two sugars are bonded through an oxygen. 57

Disaccharides 58

α β -1，4苷键 β 苷键 糖的 类型 构型 半缩醛（酮） 二糖分子含 分子有 羟基+醇羟基 半缩醛羟基 还原性 半缩醛（酮） 羟基+半缩 醛（酮）羟基 二糖分子无 半缩醛羟基 分子无 还原性 α -1，4苷键 β -1，4苷键 苷键 类型 糖的 构型 α β

双糖 非还原性二糖 蔗糖 1. 水解： 蔗糖 葡萄糖 + 果糖 2. 结构： 3. 还原性：蔗糖无半缩醛（酮）羟基，为非还原性糖 非还原性二糖 蔗糖 1. 水解： 蔗糖 葡萄糖 + 果糖 2. 结构： 麦芽糖酶或 苦杏仁酶或酸 3. 还原性：蔗糖无半缩醛（酮）羟基，为非还原性糖 蔗糖 + 本尼迪试剂

Sucrose: Linkage of Two Anomeric Carbons Some sugars are joined by a direct glycosidic linkage between their anomeric carbon atoms: a 1,1’ linkage. 61

还原性二糖 麦芽糖 2. 结构： 1. 水解 ： 麦芽糖 两分子葡萄糖 麦芽糖酶 半 缩 醛 羟 基 1. 水解 ： 麦芽糖 两分子葡萄糖 2. 结构： 麦芽糖酶 α-1，4苷键 半 缩 醛 羟 基 α-D-葡萄糖残基 α-D-葡萄糖残基 3. 还原性：麦芽糖分子有半缩醛羟基，为还原性糖 麦芽糖 + 班氏试剂 砖红色

An a-1,4’ Glucosidic Linkage 麦芽糖 Maltose contains a 1,4’ glucosidic linkage between the two glucose units. The monosaccharides in maltose are joined together by the axial position of C1 and the equatorial position of C4'. 63

纤维二糖 还原性双糖 纤维二糖的  异头物 还原性双糖 乳糖 乳糖的  异头物

A b-1-4’ Glycosidic Linkage 纤维二糖 In cellobiose, the anomeric carbon of one glucose unit is linked through an equatorial (b) carbon-oxygen bond to C4 of another glucose unit. This is called a b-1-4’ glycosidic linkage. 65

Lactose: A b-1,4' Galactosidic Linkage 乳糖 Lactose is composed of one galactose unit and one glucose unit. The two rings are linked by a b-1,4’ glycosidic bond of the galactose acetal to the 4-position on the glucose ring: a b-1,4’ galactosidic linkage. 66

多糖 1. 定义：由数百上千个单糖分子以苷键连结聚合而成 的高分子化合物 2. 水解： 多糖 单糖（最终产物） 3. 分类： 均多糖 2. 水解： 多糖 单糖（最终产物） 3. 分类： 水解 均多糖 杂多糖 一种单糖 两种以上单糖或单糖衍生物 水 解

淀粉 1. 分类： 2. 结构： 初级 螺旋状结构 高级 立体结构 几百到一万个α- D-葡萄糖残基 三万个α-D-葡 萄糖残基 20% 初级 螺旋状结构 高级 立体结构 几百到一万个α- D-葡萄糖残基 三万个α-D-葡 萄糖残基 20% 80% 直链淀粉 Amylose 支链淀粉 Amylopectin α-1，4苷键 α-1，4或 α-1，6苷键 I2进入螺旋圈 生成蓝色物质 I2进入螺旋圈 生成紫红色物质

Amylose直链淀粉& Amylopectin支链淀粉 Amylose: an a-1,4’ polymer of glucose Soluble starch, polymer of D-glucose. Starch-iodide complex, deep blue. Amylopectin: a branched a-1,6’ polymer of glucose Branched, insoluble fraction of starch.

结构：以β-1，4’苷键连结β-D-葡萄糖成线状结构 纤维素 Cellulose : synthesized by plants as a structural material to support the weight of the plant. 构成所有活的植物的细胞壁纤维组织 结构：以β-1，4’苷键连结β-D-葡萄糖成线状结构 β-1，4苷键 8000 - 10000

Amylose vs. Cellulose Different conformation glycosidic bond  a[1,4] vs b[1,4] Results in very different molecular shape in solution Amylose helix Cellulose sheets (Solomons and Fryhle, 2000; © John Wiley & Sons, Inc.)

Glycogen 糖原 & Chitin 几丁质 Glucose polymer, similar to amylopectin, but even more highly branched. The entire globular granule may contain approximately 30,000 glucose units. Energy storage in muscle tissue and liver. The many branched ends provide a quick means of putting glucose into the blood. Chitin Polymer of N-acetylglucosamine. Exoskeleton of insects.

Glycoge:2-D cross-sectional view of glycogen Glycoge:2-D cross-sectional view of glycogen. A core protein of glycogenin is surrounded by branches of glucose units.

The End Of Chap 24 Homework: