Chapter 18 Biomolecules: Carbohydrates18.1 Classification of Carbohydrates18.2 Configurations of Monosaccharides18.3 Cyclic Structures of Monosaccharides: Hemiacetal Formation18.4 Monosaccharide Anomers Mutarotation18.5 Reactions of Monosaccharides18.6 Disaccharides
Carbohydrate:( 碳水化合物 ) Cm(H2O)n
Glucose:( 葡萄糖 )
C6H12O6 C6(H2O)6
Poly-hydroxylated aldehydes and ketones Sugars:
OOH
OHHO
HOOH
COH
OHHO
OHOH
H
HH
H
CH2OH
The sugar,Starch,CelluloseNucleic acid
Monosaccharides ： a simple carbohydrate that can’t be converted into smaller sugar by hydrolysis.
Photosynthesis:( 光合作用 )
6 CO2 + 6 H2O Sunlight 6 O2 + C6H12O6
Cellulose,starch
Carbohydrates
Monosaccharides(simple sugars)
( 单糖 )Oligosaccharides
( 寡糖 )Polysaccharides
( 多糖 )
Ex. Glucose, fructose( 果糖 )
P441,14.1
P441,14.1
18.1 Classification of Carbohydrates
An oligosaccharide yields 3-10 monosaccha-rides units on hydrolysis.
Ex.: Sucrose( 蔗糖 ) Table sugarSucrose (C12H22O11) + H2O
Glucose (C6H12O6) + Fructose (C6H12O6)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-
COH
OHHO
OHOH
H
HH
H
CH2OH
Monosaccharides: tri-, tetr-, pent-, hex- and so on.
Glucose(an aldohexose)
( 己醛糖 )
CHO
OHOH
HH
H
CH2OH
O
CH2OH
Fructose(an ketohexose)
( 己酮糖 )
COH
OHOHOH
HH
H
CH2OH
(an aldopentose)( 戊醛糖 )
Ribose( 核糖 )
18.2 Configurations of Monosaccharides
D and L Designation of saccharides
COH
OHHO
OHOH
H
HH
H
CH2OH
OH CHO
OH
OH
OH
H
H
H
H
CH2OH
Turn 90°
COH
OHHCH2OH*
Glyceraldehyde( 甘油醛 )
(+)-(R)-
D-Glyceraldehyde
CO H
CH2OHHO H*
L-Glyceraldehyde
(S)-(-)-Glyceraldehyde
D: dextrorotationL: levorotation
P445,14.3
P445,14.3
L-GlyceraldehydeD-Glyceraldehyde
COH
OHOHOH
HH
H
CH2OH
COH
OHHO
OHOH
H
HH
H
CH2OH
CHO
OHOH
HH
H
CH2OH
O
CH2OH
(D)-Ribose (D)-Glucose (D)-Fructose
COH
OHHO
OHOH
H
HH
H
CH2OH
OHHO
H
HH
CH2OH
CO H
HO H
HO
(D)-Glucose (L)-Glucose
CHO
OHOH
HH
H
CH2OH
O
CH2OH
COHHH
H
CH2OH
O
CH2OH
HOHO
(D)-Fructose(L)-FructoseIn 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- memberedcyclic hemiacetal.
COH
OHHO
OHOH
H
HH
H
CH2OHD-Glucose
OH
OHOH
CH2OH
OH
O
H
D-Glucose, pyranose ( 吡喃糖 )
Haworth projection
OHOH
CH2OH
OHO OH
H
OCH2OH
HOHO
OH
OHP450P450
Sir (Walter) Norman Haworth
1883-1950
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 namedascorbic 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.
http://www.nobel.se/chemistry/laureates/1937/haworth-bio.html
Conversion from Fischer projection to Haworth projection:
COH
OHHO
OHOH
H
HH
H
CH2OH
CO
HOH
HOHO
HHH
H
HOCH2
OH
Turn 90°
Bend OH CHO
OH
OHOH
CH2OH Turn C4 C5 bondin anticlockwise OH
OHOH
CH2OH
OH CHO
OHOH
CH2OH
OHO OH
H
Close ring
1
23
4
5
OH
OHOH
CH2OH
OH CHO
OHOH
CH2OH
OHO
OH
H+
OHOH
CH2OH
OHO OH
H
18.4 Monosaccharide Anomers ( 差向异构体 ) : Mutarotation( 变旋现象 )
D-Glucoseα-D-Glucopyranose
Trans
β-D-Glucopyranose36 ： 64
mp ： 146° 148-155°[α]D: +112.2° +18.7°
[α]D: +52.6°In a aqueous solution ofpure anomer:
CisP452,14.6P452,14.6
Trans
OCH2OH
HOHO
OH
OHO
CH2OH
HOHO
OHOH
α-D-Glucopyranose ( 吡喃葡萄糖 )
β-D-Glucopyranose ( 吡喃葡萄糖 )
Cis
18.5 Reactions of MonosaccharidesGlycoside Formation( 糖苷的生成 ):
The treatment of a hemiacetal with an alcohol in the present of an acid yields anacetal:
C OR
OH
+ ROHH+
C OR
OR
A saccaharide hemiacetal reacts with an alcohol under catalyisis of an acid to yieldAn acetal:
OCH2OH
HOHO
OH
OH + ROHH+ O
CH2OH
HOHO
OHOCH3
OCH2OH
HOHO
OH
OCH3+
β-D-GlucopyranoseMethyl-α-D-glucopyranoside( 甲基 -D- 吡喃葡萄糖苷 )(66%)
β-(33%)
P454,14.7P454,14.7
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:
OCH2OH
HOHO
OH
O
CO2H
Salicin( 水杨苷 )
OCH2OH
HOHO
OH
O CHO
CH3O
Vanillic β-D-Glucopyranose( 香兰素 -β-D- 吡喃葡萄糖苷 )
OCH2OH
HOHO
OH
O
OCH2
HOHO
OH
O CH
CNLaetrile
( 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
14‘
OCH2OH
HOHO
OHO
OCH2OH
HOOH
H
OH
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 bondα- 1,4'glycosidic bond
A hemiacetalgroup
A hemiacetalgroup
β- 1,4'glycosidic bondβ- 1,4'glycosidic bond
4‘
1
OCH2OH
HOHO
OHO
OCH2OH
HOOH
OH
H
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.
OCH2OH
HOHO
OHO
CH2OH
OH
HO
CH2OHO
Sucrose( 蔗糖 ), a 1,2'-glycoside
12'
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
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