Chapter 18 Biomolecules: Carbohydrates 18.1 Classification of Carbohydrates 18.2 Configurations of Monosaccharides 18.3 Cyclic Structures of Monosaccharides: Hemiacetal Formation 18.4 Monosaccharide Anomers Mutarotation 18.5 Reactions of Monosaccharides 18.6 Disaccharides

Carbohydrate: ( 碳水化合物 ) C m (H 2 O) n Glucose: ( 葡萄糖 ) C 6 H 12 O 6 C 6 (H 2 O) 6 Poly-hydroxylated aldehydes and ketones Sugars: The sugar, Starch, Cellulose Nucleic acid

Monosaccharides ： a simple carbohydrate that can’t be converted into smaller sugar by hydrolysis. Photosynthesis: ( 光合作用 ) Cellulose, starch Carbohydrates Monosaccharides (simple sugars) ( 单糖 ) Oligosaccharides ( 寡糖 ) Polysaccharides ( 多糖 ) Ex. Glucose, fructose ( 果糖 ) P441, 14.1 P441, Classification of Carbohydrates

An oligosaccharide yields 3-10 monosaccha- rides units on hydrolysis. Ex.: Sucrose ( 蔗糖 ) Table sugar Sucrose (C 12 H 22 O 11 ) + H 2 O Glucose (C 6 H 12 O 6 ) + Fructose (C 6 H 12 O 6 ) Disaccharide ( 双糖 ) Polysaccharides : hydrolyzed to more than 10 monosaccharide units. Ex.: Cellulose hydrolysis ~3000 Glucose Polyhydroxy aldehydes Polyhydroxy ketones Monosaccharides Aldoses ( 醛糖 ) Ketoses ( 酮糖 ) -ose: carbohydrate; The nature of the carbonyl group Aldo- Keto-

Monosaccharides: tri-, tetr-, pent-, hex- and so on. Glucose (an aldohexose) ( 己醛糖 ) Fructose (an ketohexose) ( 己酮糖 ) (an aldopentose) ( 戊醛糖 ) Ribose ( 核糖 )

18.2 Configurations of Monosaccharides D and L Designation of saccharides Turn 90° * Glyceraldehyde ( 甘油醛 ) (+)-(R)- D-Glyceraldehyde * L-Glyceraldehyde (S)-(-)-Glyceraldehyde D: dextrorotation L: levorotation P445, 14.3 P445, 14.3

L-GlyceraldehydeD-Glyceraldehyde

(D)-Ribose(D)-Glucose(D)-Fructose (D)-Glucose(L)-Glucose (D)-Fructose (L)-Fructose In Fischer projection, the -OH group at the lowest stereocenter: (D) for right; (L) for left. In Fischer projection, the -OH group at the lowest stereocenter: (D) for right; (L) for left.

18.3 Cyclic Structures of Monosaccharides: Hemiacetal Formation Intramolecular nucleophilic addition: the formation of a five- or six- membered cyclic hemiacetal. D-Glucose D-Glucose, pyranose ( 吡喃糖 ) Haworth projection P450

Sir (Walter) Norman Haworth Haworth made basic contributions to carbohydrate chemistry. He introduced, in 1925, the correct cyclic model for glucose, and structures of other monosaccharides (mannose, galactose, fructose) were soon added. These were followed by structural work on disaccharides (maltose, cellobiose, lactose) and eventually the poly- saccharides starch, cellulose, inulin, glycogen and xylan. Haworth also established the correct structure of Vitamin C (which he named ascorbic acid), and his synthesis constituted the first synthesis of any vitamin. Haworth was awarded the 1937 Nobel Prize in Chemistry (shared with Paul Karrer) for his research on carbohydrates and Vitamin C. He was the first British organic chemist to receive the Nobel. chemistry/laureates/ 1937/haworth-bio.html

Conversion from Fischer projection to Haworth projection:

18.4 Monosaccharide Anomers ( 差向异构体 ) : Mutarotation ( 变旋现象 ) D-Glucose α-D-Glucopyranose Trans β-D-Glucopyranose 36 ： 64 mp ： 146° ° [ α ] D : ° ° [α] D : +52.6° In a aqueous solution of pure anomer: Cis P452, 14.6 P452, 14.6

Trans α-D-Glucopyranose ( 吡喃葡萄糖 ) β-D-Glucopyranose ( 吡喃葡萄糖 ) Cis

18.5 Reactions of Monosaccharides Glycoside Formation ( 糖苷的生成 ): The treatment of a hemiacetal with an alcohol in the present of an acid yields an acetal: A saccaharide hemiacetal reacts with an alcohol under catalyisis of an acid to yield An acetal: β-D-Glucopyranose Methyl-α-D-glucopyranoside ( 甲基 -D- 吡喃葡萄糖苷 )(66%) β - (33%) P454, 14.7 P454, 14.7

The features of the reaction: (1)The anomeric –OH has been replaced by an –OR group. (2) The products─glycosides are stable to neutral water. They aren’t in equibrium with an open-chain form, and they don’t show mutarotation. Glycosides are widespread in nature: Salicin ( 水杨苷 ) Vanillic β-D-Glucopyranose ( 香兰素 -β-D- 吡喃葡萄糖苷 )

Laetrile ( 苦杏仁苷 ) 18.6 Disaccharides ( 双糖 ) Disaccharides are carbohydrates that yield two monosaccharide molecules on hydrolysis. Disaccharades are glycosides in which the alkoxy group attached to the anomeric carbon is derived from a secondary sugar molecules. P460, 14.9 P460, 14.9

1 4‘ Maltose ( 麦芽糖 ), a 1,4'- α -glycoside [4-O-(α-D-Glucopyranosyl)- α-D-Glucopyranose] [4-O-(α-D- 吡喃葡萄糖苷基 )- α-D- 吡喃葡萄糖苷 ] α- 1,4'glycosidic bond A hemiacetal group A hemiacetal group

β- 1,4'glycosidic bond 4‘ 1 Cellobiose ( 纤维二糖 ) ， aβ-1,4'-glycoside [4-O-(β-D-Glucopyranosyl)- β-D-Glucopyranose] [4-O-(β-D- 吡喃葡萄糖苷基 )- β-D- 吡喃葡萄糖苷

Both Maltose and Cellobiose are reducing sugars. Both are in equilibrium with aldehyde forms,which can reduce Tollens’ of Fehling’s reagent. Both exhibit mutarotation. Both have dramatic different biological properties. Sucrose ( 蔗糖 ), a 1,2'-glycoside 1 2'2' Fructose [2-O-( α -D-Glucopyranosyl)- β-D-fructofuranoside] [ 2-O-( α -D- 吡喃葡萄糖苷基 )- β-D- 呋喃果糖苷

Sucrose