Upload
morgan-baker
View
231
Download
4
Embed Size (px)
Citation preview
2020
20-1© 2006 Thomson Learning, Inc.All rights reserved
Chair ConformationsChair Conformations• For pyranoses, the six-membered ring is more accurately represented as a chair chair conformationconformation.
OCH2OH
HOHO
OHOH()
CHOH
HO
CH2OHOHHO
OHO
OH()HO
HO
CH2OHO
(-D-Glucose)
(-D-Glucose)
-D-Glucopyranose
-D-Glucopyranose
D-Glucose
anomericcarbon
2020
20-2© 2006 Thomson Learning, Inc.All rights reserved
Chair ConformationsChair Conformations• In both Haworth projections and chair conformations, the orientations of groups on carbons 1- 5 of -D-glucopyranose are up, down, up, down, and up.
OCH2OH
HOHO
OHOH()H
H OH
HHO
HOH()
OH
H
CH2OHO
-D-Glucopyranose(chair conformation)
-D-Glucopyranose(Haworth projection)
123
4
5
6
1
23
4
5
6
2020
20-3© 2006 Thomson Learning, Inc.All rights reserved
MutarotationMutarotation• Mutarotation: Mutarotation: the change in specific rotation that accompanies the equilibration of - and -anomers in aqueous solution.• Example: when either -D-glucose or -D-glucose is dissolved in water, the specific rotation of the solution gradually changes to an equilibrium value of +52.7°, which corresponds to 64% beta and 36% alpha forms.
[]D25 = + 18.7°
-D-Glucopyranose-D-Glucopyranose[]D
25 = +112°
OHOH
HOHO
CH2OHO HO OH
OC
CH2OH
HO
HOH
OCH2OH
HO
HOOH
HO
Open-chain form
2020
20-4© 2006 Thomson Learning, Inc.All rights reserved
Physical PropertiesPhysical Properties• Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol• Sweetness relative to sucrose:
Carbohydrate
fructose
glucose
galactose
sucrose (table sugar)
lactose (milk sugar)
honey
SweetnessRelative to Sucrose
1.741.000.970.74
0.320.16
Artificial Sweetener
SweetnessRelative to Sucrose
maltose 0.33
saccharin 450acesulfame-K 200aspartame 180
2020
20-5© 2006 Thomson Learning, Inc.All rights reserved
Formation of GlycosidesFormation of Glycosides• Treatment of a monosaccharide, all of which exist almost exclusively in cyclic hemiacetal forms, with an alcohol gives an acetal.
Acetals α + βMutarotation = No
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH
+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
Hemiacetal mutarotation =Yes
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH
+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
yes no
2020
20-6© 2006 Thomson Learning, Inc.All rights reserved
Formation of GlycosidesFormation of Glycosides• A cyclic acetal derived from a monosaccharide is called a
glycosideglycoside.•The bond from the anomeric carbon to the -OR group is called a glycosidic bondglycosidic bond.
•Mutarotation is not possible in a glycoside because an acetal, unlike a hemiacetal, •is not in equilibrium with the open-chain carbonyl-containing compound.
Glycosides are stable in water and aqueous base, but like other acetals, are hydrolyzed in aqueous acid to an alcohol
and a monosaccharide.
•Glycosides are named by listing the alkyl or aryl group bonded to oxygen followed by the name
of the carbohydrate in which the ending -ee is replaced by -ide-ide.
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH
+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
HH OH
HHO
HOH
OH
H
CH2OHO
CH3OHH+
-H2O
OCH2OH
H
OH
OCH3H
HOH
OHH
H
OCH2OH
H
OH
HH
HOH
OHH
OCH3
(-D-Glucose)-D-Glucopyranose
Methyl -D-glucopyranoside(Methyl -D-glucoside)
anomeric carbon
+
+
Methyl -D-glucopyranoside(Methyl -D-glucoside)
glycosidicbond
2020
20-7© 2006 Thomson Learning, Inc.All rights reserved
Reduction to AlditolsReduction to Alditols• The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2 in the presence of a transition metal catalyst.• The reduction product is called an alditolalditol.
OHOH
HOHO
CH2OHO
CHOOHHHHOOHH
CH2OHOHH
NaBH4
CH2OHOHHHHOOHH
CH2OHOHH
D-Glucitol(D-Sorbitol)
D-Glucose-D-Glucopyranose
alditol
2020
20-8© 2006 Thomson Learning, Inc.All rights reserved
Reduction to AlditolsReduction to Alditols• Sorbitol is found in the plant world in many berries and in cherries, plums, pears, apples, seaweed, and algae.
• It is about 60 percent as sweet as sucrose (table sugar) and is used in the manufacture of gums, candies and as a sugar substitute for diabetics.
CH2OH
CH2OH
OHHOHH
CH2OH
CH2OH
OHHHHOOHH
CH2OHHHOHHOOHH
CH2OHOHH
D-Mannitol XylitolErythritol
OHOH
HOHO
CH2OHO
CHOOHHHHOOHH
CH2OHOHH
NaBH4
CH2OHOHHHHOOHH
CH2OHOHH
D-Glucitol(D-Sorbitol)
D-Glucose-D-Glucopyranose
•These four alditols are also common in the biological world.
2020
20-9© 2006 Thomson Learning, Inc.All rights reserved
Oxidation to Aldonic Oxidation to Aldonic AcidsAcids
• The aldehyde group of an aldose is oxidized under basic conditions to a carboxylate anion.
• The oxidation product is called an aldonic acidaldonic acid.• A carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing reducing sugarsugar (it reduces the oxidizing agent).
OCH2OH
HOHO
OHOH
COHHHHOOHH
CH2OHOHH
O HC
OHHHHOOHH
CH2OHOHH
O O-
oxidizingagent
D-GluconateD-Glucose-D-Glucopyranose(-D-Glucose)
basicsolution
enediol intermed.
2020
20-10© 2006 Thomson Learning, Inc.All rights reserved
Oxidation to Uronic AcidsOxidation to Uronic Acids• Enzyme-catalyzed oxidation of the primary alcohol at C-6 of a hexose yields a uronic aciduronic acid.
Fisher proj.
Chair conformation
CHO
CH2OH
OHHHHOOHHOHH
D-Glucose
enzyme-catalyzedoxidation
CHO
COOH
OHHHHOOHHOHH
D-Glucuronic acid(a uronic acid)
OHO
HOOH
OH
COOH
e.g. Enzyme-catalyzed oxidation of D-glucose,
yields D-glucuronic acid.
2020
20-11© 2006 Thomson Learning, Inc.All rights reserved
D-Glucuronic AcidD-Glucuronic Acid• D-Glucuronic acid is widely distributed in the plant and animal world.
OHOHO
OHO
COO-
HO
Propofol A urine-soluble glucuronide
OHOHO
OHO
COO-
HO
Propofol A urine-soluble glucuronide
•In humans, it is an important component of the acidic polysaccharides of connective tissues, e.g. collagen.
Used by the body to detoxify foreign phenols and alcohols; in the liver, compounds converted to glycosides of
glucuronic acid and excreted in the urine.
2020
20-12© 2006 Thomson Learning, Inc.All rights reserved
Two Volunteers Two Volunteers needed. . .needed. . .
1 male1 female
2020
20-14© 2006 Thomson Learning, Inc.All rights reserved
Phosphate EstersPhosphate Esters• Mono- and diphosphoric esters are intermediates in the metabolism of monosaccharides.•For example, the first step in glycolysis is conversion of
•D-glucose to a-D-glucose 6-phosphate.
•Note that at the pH of cellular and intercellular fluids, both acidic protons of a diphosphoric ester are ionized, giving it a charge of -2.
2020
20-15© 2006 Thomson Learning, Inc.All rights reserved
DisaccharidesDisaccharides
O
HOOH
OH
CH2OH
O
OH
HOO
CH2OH
HOCH2
OHO
HO
O
OH
CH2OH
OH
HOO
CH2OH
HOCH2
1
1
2
1
2
1
a unit of -D-glucopyranose
a unit of -D-fructofuranose
-1,2-glycosidic bond
e.g. Sucrose (table sugar)Sucrose is the most abundant disaccharide in the biological world; it is obtained principally from
the juice of sugar cane and sugar beets.
•Sucrose is a nonreducing sugar.
2020
20-16© 2006 Thomson Learning, Inc.All rights reserved
DisaccharidesDisaccharides• Lactose
Lactose sugar present in milk; 5-8% human milk, 4-6% cow's milk.
O
OH
HOOH
O
CH2OH
O
HOOH
OH
CH2OHOOH O
OH
OH
CH2OH
O OH
OH
OH
CH2OH
1
1
4
4
-1,4-glycosidic bond
•Little sweetness: added to cheap foods ~ fillers . . .
•D-galactopyranose bonded by a b-1,4-glycosidic bond to carbon 4 of D-glucopyranose.
•Lactose is a reducing sugar. Why? In equilb. w/ Open chain form~ can be oxidized to carboxylate
OCH2OH
HOHO
OHOH
COHHHHOOHH
CH2OHOHH
O HC
OHHHHOOHH
CH2OHOHH
O O-
oxidizingagent
D-GluconateD-Glucose-D-Glucopyranose(-D-Glucose)
basicsolution
2020
20-17© 2006 Thomson Learning, Inc.All rights reserved
A, B, AB and O Blood A, B, AB and O Blood typestypes
2020
20-19© 2006 Thomson Learning, Inc.All rights reserved
DisaccharidesDisaccharides• Maltose
• Present in malt, the juice from sprouted barley and other cereal grains.
• Maltose consists of two units of D-glucopyranose joined by an -1,4-glycosidic bond.
• Maltose is a reducing sugar.
OHO
HOOH
OOHO OH
OH
CH2OH
CH2OHO
OH
O
OHHO
O OH
HO
OH
CH2OH
HOCH2 1
4
-1,4-glycosidicbond1 4
2020
20-20© 2006 Thomson Learning, Inc.All rights reserved
PolysaccharidesPolysaccharides• Polysaccharide:Polysaccharide: a carbohydrate of many monosaccharides joined by glycosidic bonds.
• Starch:Starch: a polymer of D-glucose, E stores in plants
• Two forms: amylose and amylopectin.
• 25% Amylose, unbranched chains w/ 4000 D-glucose units joined by -1,4-glycosidic bonds.
• 75% Amylopectin, has branched chains with up to 10,000 D-glucoses, joined by -1,4-glycosidic bonds;
at branch points, new chains of 24 to 30 units are started by -1,6-glycosidic bonds.
2020
20-21© 2006 Thomson Learning, Inc.All rights reserved
PolysaccharidesPolysaccharides• Figure 20.3 Amylopectin.
2020
20-22© 2006 Thomson Learning, Inc.All rights reserved
PolysaccharidesPolysaccharides• GlycogenGlycogen is the energy-reserve carbohydrate for animals.• Glycogen is a branched polysaccharide of approximately 106 glucose units joined by -1,4- and -1,6-glycosidic bonds.
• The total amount of glycogen in the body of a well-nourished adult human is about 350 g, divided almost equally between liver and muscle.
2020
20-23© 2006 Thomson Learning, Inc.All rights reserved
PolysaccharidesPolysaccharides• CelluloseCellulose linear polysaccharide - D-glucose units, -
1,4-glycosidic bonds.• ~ molecular weight of 400,000 g/mol, corresponding to
approximately 2200 glucose units per molecule.
• Cellulose align themselves side by side into fibers . . OH groups form numerous intermolecular H-bonds.
• This arrangement of parallel chains in bundles gives cellulose fibers their high mechanical strength.
• reason why cellulose is insoluble in water.
2020
20-24© 2006 Thomson Learning, Inc.All rights reserved
PolysaccharidesPolysaccharides
• Cellulose (cont’d)• Humans can’t use cellulose, lack digestive enzymes -
glucosidases, catalyze hydrolysis of -glucosidic bonds.
• Humans have only -glucosidases; hence, the polysaccharides we use as sources of glucose are starch and glycogen.
• Many bacteria and microorganisms have -glucosidases and can digest cellulose.
• Termites have such bacteria in their intestines and can use wood as their principal food.
• Ruminants (cud-chewing animals) and horses can also digest grasses and hay.
2020
20-25© 2006 Thomson Learning, Inc.All rights reserved
Acidic Acidic PolysaccharidesPolysaccharides• Acidic polysaccharides:Acidic polysaccharides: a group of
polysaccharides that contain carboxyl groups and/or sulfuric ester groups, and play important roles in the structure and function of connective tissues.
• There is no single general type of connective tissue.
• Large number of highly specialized forms, such as cartilage, bone, synovial fluid, skin, tendons, blood vessels, intervertebral disks, and cornea.
• Most connective tissues are made up of collagen, a structural protein, in combination with a variety of acidic polysaccharides.
2020
20-26© 2006 Thomson Learning, Inc.All rights reserved
Acidic Acidic PolysaccharidesPolysaccharides• e.g. Hyaluronic acide.g. Hyaluronic acid
• contains from 300 to 100,000 repeating units.
• is most abundant in embryonic tissues, connective tissues (synovial fluid) the lubricant of joints
-the vitreous of the eye: provides a clear, elastic gel that maintains the retina in its proper position
O
HOOH
COO-
OHO
NH
CH2OH
CH3C O
O O
The repeating unit of hyaluronic acid
4
13
1
3
4
D-glucuronic acid N-Acetyl-D-glucosamine
2020
20-27© 2006 Thomson Learning, Inc.All rights reserved
Acidic Acidic PolysaccharidesPolysaccharides• HeparinHeparin: a heterogeneous mixture of
variably sulfonated polysaccharide chains, ranging in molecular weight from 6,000 to 30,000 g/mol.
2020
20-28© 2006 Thomson Learning, Inc.All rights reserved
Acidic Acidic PolysaccharidesPolysaccharides• Heparin (cont’d)
• Heparin is synthesized and stored in mast cells of various tissues, particularly the liver, lungs, and gut.
• The best known and understood of its biological functions is its anticoagulant activity (blood thinner).
• It binds strongly to antithrombin III, a plasma protein involved in terminating the clotting process.