Transcript Camp 1
20 Chapter 20, actually (CHPT 19) Carbohydrates © 2006 Thomson Learning, Inc. All rights reserved 20-1 20 Carbohydrates •Carbohydrate: a polyhydroxyaldehyde or polyhydroxyketone, •or a substance that gives these compounds on hydrolysis. Most simple carbos = Saccharides e.g. monosaccharides,, oligosaccharides, polysachrides, dep. On # of simple sugars attached •Monosaccharide: a carbohydrate that cannot be •hydrolyzed to a simpler carbohydrate. © 2006 Thomson Learning, Inc. All rights reserved 20-2 20 Monosaccharides • general formula CnH2nOn, where n varies from 3 to 8. C6H12O6 Two Types: Aldose: a monosaccharide containing an aldehyde group. Ketose: a monosaccharide containing a ketone group. © 2006 Thomson Learning, Inc. All rights reserved 20-3 20 Monosaccharides • classified by their number of carbon atoms. Name Form ul a Tri ose Te trose C3 H6 O3 C4 H8 O4 Pe n tos e C5 H1 0 O 5 He xose C6 H1 2 O 6 He ptos e C7 H1 4 O 7 C8 H1 6 O 8 O ctos e © 2006 Thomson Learning, Inc. All rights reserved 20-4 20 Monosaccharides • There are only two trioses: CHO CH2 OH CHOH C= O CH2 OH CH2 OH Gl yce ralde h yde (an aldotri ose ) Di hydroxyace ton e (a k e totri ose ) •Often aldo- and keto- are omitted •compounds are referred to simply as trioses. •Although “triose” does not tell the nature of the carbonyl group, •it at least tells the number of carbons. © 2006 Thomson Learning, Inc. All rights reserved 20-5 20 Monosaccharides • Glyceraldehyde, the simplest aldose, contains a stereocenter and exists as a pair of enantiomers. Fig 19.1 © 2006 Thomson Learning, Inc. All rights reserved 20-6 20 Monosaccharides •Fischer projection: a two dimensional representation showing the configuration of stereocenters. •Horizontal lines represent bonds projecting forward from the stereocenter. •Vertical lines represent bonds projecting to the rear. •Only the stereocenter is in the plane. 2,3 hydroxy propanal CHO H C R OH CH2 OH © 2006 Thomson Learning, Inc. All rights reserved con vert to a Fischer projection CHO H R OH CH2 OH 20-7 20 D,L Monosaccharides • 1891, E. Fischer arbitrary assignments D/L to the enantiomers of glyceraldehyde. NOTE: R=D L=S CHO H OH CH2 OH CHO HO H CH2 OH (R) D-Glyce ral de h yde (S) L-G lyce ral de h yde 25 []D = +13.5° Dextrorotatory 25 []D = -13.5° levatory •D-monosaccharide: the -OH on penultimate carbon on right •L-monosaccharide: the -OH on penultimate carbon on left in a Fischer projection. © 2006 Thomson Learning, Inc. All rights reserved 20-8 20 D,L Monosaccharides • Suffix “ose” indicates compound = carbo Nature predominately makes the D form as well “D amino acids” discussed later… •The most common D-tetroses and D-pentoses are: CHO H CHOOH HH OH OH H OH CH2 OH CH2 OH D-Eryth rose D-Eryth rose CHO HOCHO H HOH H OH H OH CH2 OH CHre 2 OH D-Th ose D-Th re ose CHO CHO H CHO OH H CHOH HH OH HH H OH OH H HH OH H OH OH OH H OH H OH CH2 OH CH2 OH CH2 OH 2-De oxy-D-ri CH2 OHbos e D-Ribose D-Ribose 2-De oxy-D-ri bos e Note: “D,L” specifies configuration @ stereocenter farthest from Carbonyl © 2006 Thomson Learning, Inc. All rights reserved 20-9 20 D,L Monosaccharides The three most common D-hexoses are: H HO H H CHO OH H OH OH CH2 OH D-G l ucos e H HO HO H CHO CHO CH2 OH CHO OHH OH C= O H OH HHO HO H HO H H H H OHH OHHO H OH H OHH OH H OH CH2 OH CH OHCH2 OH CH OH 2 2 D-G alactoseD-G l ucos D-Fructose e D-G alactose CH2 OH C= O HO H H OH H OH CH2 OH D-Fructose aka blood sugar Human blood~65-110 mg glucose/100ml blood I.V. bags contain 5% glucose solut. © 2006 Thomson Learning, Inc. All rights reserved 20-10 20 Amino Sugars • Amino sugars: Have -NH2 group in place of an -OH group. Only three amino sugars are common in nature: D-glucosamine, D-mannosamine, and D-galactosamine H HO H H CHO OH H OH OH CH2 OH D-G l ucos e CHO CHO CH OH O O CHO CHO CHO 2 CHO 2 N 2 H N HCCH O H 2 NHC= 2 H H HN H2N H2 H HN HCCH 3 3 HO HO HOH H H HO HOH H HO HOH H 4 HH H OH OH OH HO 4HOH H H HOH OH HH H OH OH OH H HOH OH H HOH OH CH OH CH22CH OH2 OH CH2CH OH2 OH CH 2CH OH2 OH D-G alactose D-Glu cosami n e D-Fructose D-Man n osam e D-Gal actos e N-Ace tyl-DD-Glu cosami n e D-Man n osam in e inD-Gal actos amiami n e nN-Ace tyl-D-2 s tere ois ome -4 s tere ois ome r cosami glu cosami (C -2(Cs tere ois ome r (Cr-4(Cs tere ois ome r glu ne ne of D-glu cos ami n eD-gl of D-gl cosin am of D-glu cos ami n e of u cosuam e )in e ) CHO CHO CHO N H2 H HHN HOH 2 HOH HH HOHO HHOHOHHOH OH H HHOHOH CH2 2OH OH CHCH 2 OH © 2006 Thomson Learning, Inc. All rights reserved 20-11 20 Amino Sugars HO N H2 H H OH H2 OH H HO H H CHO O N HCCH 3 H OH OH CH 2 OH os ami n e N-Ace tyl-Dois ome r glu cosami n e os am in e ) © 2006 Thomson Learning, Inc. All rights reserved 20-12 20 Cyclic Structure of monosaccharides • RECALL: 17.7 • Aldehydes and ketones react with alcohols to form hemiacetals. •From one stereocenter (aldehyde/alcohol) to two (hemiacetal) © 2006 Thomson Learning, Inc. All rights reserved 20-13 20 Haworth Projections • D-Glucose forms these cyclic hemiacetals. 1 1 1CHO red raw to sh ow th e -OH CH2 OH CHO redraw rawtotoshshow owththeto e-OH -OH CHO red on carbon-5 close the OH CH H OH 2 OH 2OH 5 CH on carbon-5 close to the on carbon-5 close to the H5 5 OH HH OH aldeh yd e on carbon-1 OH O HH OH H HO H aldehydyde eononcarbon-1 carbon-1 aldeh OO HO HH HO H H CC H OH H OH OHHHC1 H OH HO 11 OH HH 5 OH HO HO HH H 5 5 OH New stereogenic center H OH OH HH OH HH OH = anomeric carbon OH CH2 OH CH CH 2 OH 2 OH anomeric CH2 OH anomeric CH2 OH D -Glucose CH OH anomeric CH CH OH CH carb on -Glucose DD-Glucose 2O 2 OH 2O 2 OH H carbonon carb H ( ) H OH O O O O H H HHH H HH OH OH( ( ) ) + H H OH H H H OH ++ H OH OH OH OH HO HO HHOH( ) HHH HO HO HO HO ( ( )) OH OH HH H OH H OH HH OH HH OH OH OH -D -Glucopyranose -D -Glucopyranose -D -Glucopyranose -D -Glucopyranose -D -Glucopyranose -D -Glucopyranose © 2006 Thomson Learning, Inc. (-D -Glucose) ( -D -Glucos e ) All rights reserved (-D-Glucose) -Glucose) (-D ( -D -Glucose )e ) ( -D -Glucos 20-14 20 Haworth Projections 1 • CHO H OH red raw to sh ow th e -OH on carbon-5 close to the aldeh yd e on carbon-1 H In the terminology of carbohydrate HO chemistry, H OH 5 H are OH called anomers Stereoisomers that differ in configuration only at anomeric carbon 1 CHO H OH CH2 OH red raw to sh ow th e -OH on carbon-5 close to the aldeh yd e on carbon-1 HOcarbon H • β means -OH on anomeric same side of ring H H OH 5 OH D -Glucose CH2 OH 5 OH H O -CH2OH. as theH terminal OH H C1 HO H H CH2 OH •α OH CH2 OH anomeric CH2 OH carb on OH means -OH on anomeric carbon is on side of the ring H O OH H ( ) H H + opposite from the terminal -CH2OH. OH H OH H HO HO OH( ) H H OH H OH -D -Glucopyranose -D -Glucopyranose (-D -Glucose) ( -D -Glucos e ) D -Glucose CH2 OH O OH ( ) H H OH H HO H H OH -D -Glucopyranose (-D -Glucose) six-membered hemiacetal ring :pyranose, five-membered hemiacetal ring: furanose. © 2006 Thomson Learning, Inc. All rights reserved O O Furan Pyran 20-15 20 Haworth Projections • Aldopentoses also form cyclic hemiacetals. The most prevalent forms of D-ribose/ other pentoses are furanoses. HOCH HOCH22 OO HOCH HOCH22 OO HH OH OH () () HOCH2 HOCH2 H OH () HH O HH HH O HH H H H H HH OH OH() () HH HH H OH OH () H OH OH OH OH OH HHH OH OH H -2-D -2-DOH eoxy-D eoxy-D-ribofuranose -ribofuranose -D -D-Ribofuranose -Ribofuranose -2-D eoxy-D -ribofuranose -D -Ribofuranose (-2-D (-2-D eoxy-D eoxy-D -rib -ribos ose) e) (-D (-D-Rib -Ribos ose) e) (-2-D eoxy-D -rib os e) (-D -Rib os e) •The prefix “deoxy” means “without oxygen.” © 2006 Thomson Learning, Inc. All rights reserved 20-16 20 Haworth Projections • D-Fructose (a 2-ketohexose) also forms a fivemembered cyclic hemiacetal. HOCH2 5 1 O H HO CH2 OH 2 OH( ) H HO H -D -Fructofuranose ( - D -Fructos e) 1 CH2 OH 2 C=O HO H H OH H 5 OH CH2 OH D -Fru ctose Where is the anomeric carbon? © 2006 Thomson Learning, Inc. All rights reserved HOCH2 5 O H HO H OH ( ) 2 CH2 OH HO H 1 - D -Fru ctofu ran os e (- D -Fructose) 20-17 20 Chair Conformations >> Haworth projected anomeric anomeric carbon carbon CH OH six-membered ring is more CH 2 the 2 OH • For pyranoses, OO HO HO HO accuratelyHO represented OH() OH()as a chair conformation. OH OH -D-D -Glu -Glucopyran copyranososee ( (-D -Glucos -D -Glucose)e) anomeric carbon CH CH22OH OH CH2 OH HO HO OH OH O HO HO HO O O HO OH() CC OH OH OH HH -D -Glu copyran os e -Glucosee DD-Glucos ( - D -Glucos e) CH OH HO form 2 OH Most common HO vs axial O b/c OH in equatorial C (more stable) OH H The above D -Glucos e © 2006 Thomson Learning, Inc. All rights reserved HO HO HO HO CH22OH OH O O HO HO OH( ) OH( ) -- D -Glu copyran copyranos osee (( --D D -Glucose) -Glucose) CH2 OH O HO OH( ) are in equilib. In aqueous solut. - D -Glu copyran os e ( - D -Glucose) 20-18 20 Chair Conformations • In both Haworth projections and chair conformations, the orientations of groups on carbons 1- 5 of -Dglucopyranose are up, down, up, down, and up. 6 CH2 OH 5 O OH() H H 4 OH 1 H HO H 3 2 H OH -D -Glucop yranose (Haw orth p rojection) © 2006 Thomson Learning, Inc. All rights reserved 6 CH2 OH 4 HO HO O 5 3 2 OH 1 OH( ) - D -Glucopyranose (ch air con formation) 20-19 20 Mutarotation •change in mea. specific rotation that accompanies the equilibration of alpha and beta anomers in aqueous solution. • e.g : -D-glucose or -D-glucose into H2O . . . specific rotation of solution changes to an equilibrium of +52.7°(64% beta & 36% alpha forms). HO HO CH2 OH O OH OH -D -Glucopyranose [] D 2 5 = + 18.7° © 2006 Thomson Learning, Inc. All rights reserved HO HO CH2 OH OH O C HO H Open-chain form HO HO CH2 OH O HO OH -D -Glucopyranose [] D 2 5 = +112° 20-20 20 Physical Properties • Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol • Sweetness relative to sucrose: S w eetness Relative to Carbohydrate S ucrose fructos e 1.74 sucrose (tab le sugar) 1.00 honey 0.97 glu cose 0.74 maltose 0.33 galactos e 0.32 lactose (milk su gar) 0.16 © 2006 Thomson Learning, Inc. All rights reserved S w eetness Relative to Artificial Sw eetener S ucrose saccharin 450 acesu lfame-K 200 aspartame 180 20-21 20 Formation of Glycosides • Treatment of a monosaccharide, all of which exist almost exclusively in cyclic hemiacetal forms, with an alcohol gives an acetal. anomeric carbon CH2 OH O OH H + H H + CH3 OH OH H -H2 O HO H glycos idic H OH CH2 OH bond -D -Glu copyran os e O OCH3 H (-D -Glu cose) H + OH H H HO © 2006 Thomson Learning, Inc. All rights reserved CH2 OH OH H H OH H HO OCH3 H OH H OH Methyl -D -glu copyran os ide Methyl -D -glu copyran os ide (Methyl -D -glu coside) (Methyl -D -glucos ide) 20-22 20 Formation of Glycosides • A cyclic acetal derived from a monosaccharide is called a glycoside. • The bond from the anomeric carbon to the -OR group is called a glycosidic 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 -e is replaced by -ide. © 2006 Thomson Learning, Inc. All rights reserved 20-23 20 Reduction 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 alditol. HO HO CH2 OH O OH OH -D -Glucop yranose © 2006 Thomson Learning, Inc. All rights reserved CHO H OH HO H NaBH4 H OH H OH CH2 OH D -Glu cose CH2 OH H OH HO H H OH H OH CH2 OH D -Glucitol (D -Sorbitol) 20-24 20 Reduction 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 candies and as a sugar substitute for diabetics. • These three alditols are also common in the biological world. CH2 OH CH2 OH H OH H OH CH2 OH Erythritol © 2006 Thomson Learning, Inc. All rights reserved HO HO H H H H OH OH CH2 OH D -Mannitol CH2 OH H OH HO H H OH CH2 OH Xylitol 20-25 20 Oxidation to Aldonic Acids • The aldehyde group of an aldose is oxidized under basic conditions to a carboxylate anion. • The oxidation product is called an aldonic acid. • A carbohydrate that reacts with an oxidizing agent to form an aldonic acid is classified as a reducing sugar (it reduces the oxidizing agent). O H C HO HO CH2 OH O OH OH - D-Glu copyran ose ( - D-Glu cose ) © 2006 Thomson Learning, Inc. All rights reserved O- O C H HO H H OH oxidi zi n g H OH agen t H HO H OH basi c H OH OH s ol u tion H OH CH2 OH CH2 OH D-Glu cose D-Gl u con ate 20-26 20 Oxidation to Uronic Acids • Enzyme-catalyzed oxidation of the primary alcohol at C-6 of a hexose yields a uronic acid. • Enzyme-catalyzed oxidation of D-glucose, for example, yields D-glucuronic acid. CHO e n z ym eH OH catalyz e d HO H oxidati on H OH H OH CH2 OH D-Glu cose © 2006 Thomson Learning, Inc. All rights reserved H HO H H CHO OH COOH O H HO OH HO OH OH COOH D-Glu cu ron i c aci d (a u ron i c aci d) OH 20-27 20 D-Glucuronic Acid • D-Glucuronic acid is widely distributed in the plant and animal world. • In humans, it is an important component of the acidic polysaccharides of connective tissues. • It is used by the body to detoxify foreign phenols and alcohols; in the liver, these compounds are converted to glycosides of glucuronic acid and excreted in the urine. - COO HO HO HO O O OH Propofol © 2006 Thomson Learning, Inc. All rights reserved A u rin e-s olu ble glucuronide 20-28 20 Phosphate 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 -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. © 2006 Thomson Learning, Inc. All rights reserved CHO H OH HO H H OH H OH O CH2 O-P- O OD-Glu cose 6-ph os ph ate O O P OO CH2 HO HO O HO OH -D-Gl u cos e 6-ph os ph ate20-29 20 Disaccharides • 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. CH2 OH O OH 1 HO HO OH HO OH O O HO 2 CH2 OH 1 OH HOCH2 © 2006 Thomson Learning, Inc. All rights reserved a u n i t of-Dglu copyran ose CH2 OH O HOCH2 O HO 1 O 2 -1,2-glycosi dic bon d a u n i t of-Dfru ctofu ran os e CH2 OH OH 1 20-30 20 Disaccharides • Lactose • Lactose is the principal sugar present in milk; it makes up about 5 to 8 percent of human milk and 4 to 6 percent of cow's milk. • It consists of D-galactopyranose bonded by a -1,4glycosidic bond to carbon 4 of D-glucopyranose. • Lactose is a reducing sugar. CH2 OH O CH2 OH OH O 4 OH 1 OH CH2 OH -1,4-glycosid ic bond O 4 O OH OH OH HO 1 OH O HO CH2 OH O OH OH OH © 2006 Thomson Learning, Inc. All rights reserved 20-31 20 Disaccharides • 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. 1 HOCH2 O HO CH2 OH 4 O OH OH HO OH © 2006 Thomson Learning, Inc. All rights reserved O OH HO HO -1,4-glycosi dic bon d CH2 OH O 1 OH 4 CH2 OH O O OH HO OH 20-32 20 Polysaccharides • Polysaccharide: a carbohydrate consisting of large numbers of monosaccharide units joined by glycosidic bonds. • Starch: a polymer of D-glucose. • Starch can be separated into amylose and amylopectin. • Amylose is composed of unbranched chains of up to 4000 D-glucose units joined by -1,4-glycosidic bonds. • Amylopectin contains chains up to 10,000 D-glucose units also joined by -1,4-glycosidic bonds; at branch points, new chains of 24 to 30 units are started by 1,6-glycosidic bonds. © 2006 Thomson Learning, Inc. All rights reserved 20-33 20 Polysaccharides • Figure 20.3 Amylopectin. © 2006 Thomson Learning, Inc. All rights reserved 20-34 20 Polysaccharides • Glycogen 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 wellnourished adult human is about 350 g, divided almost equally between liver and muscle. © 2006 Thomson Learning, Inc. All rights reserved 20-35 20 Polysaccharides • Cellulose is a linear polysaccharide of D-glucose units joined by -1,4-glycosidic bonds. • It has an average molecular weight of 400,000 g/mol, corresponding to approximately 2200 glucose units per molecule. • Cellulose molecules act like stiff rods and align themselves side by side into well-organized waterinsoluble fibers in which the OH groups form numerous intermolecular hydrogen bonds. • This arrangement of parallel chains in bundles gives cellulose fibers their high mechanical strength. • It is also the reason why cellulose is insoluble in water. © 2006 Thomson Learning, Inc. All rights reserved 20-36 20 Polysaccharides • Figure 20.4 Cellulose is a linear polymer containing as many as 3000 units of D-glucose joined by -1,4-glycosidic bonds. © 2006 Thomson Learning, Inc. All rights reserved 20-37 20 Polysaccharides • Cellulose (cont’d) • Humans and other animals cannot use cellulose as food because our digestive systems do not contain glucosidases, enzymes that catalyze hydrolysis of glucosidic bonds. • Instead, we 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 © 2006 Thomson Learning, Inc. All rights reserved digest grasses and hay. 20-38 20 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. • Rather, there are a 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. © 2006 Thomson Learning, Inc. All rights reserved 20-39 20 Acidic Polysaccharides • Hyaluronic acid • contains from 300 to 100,000 repeating units. • is most abundant in embryonic tissues and in specialized connective tissues such as synovial fluid, the lubricant of joints in the body, and the vitreous of the eye where it provides a clear, elastic gel that maintains the retina in its proper position D -glucu ronic acid N-Acetyl-D -glu cosamine - 4 HO COO 3 4 O HO O 1 OH CH2 OH O 1 3 O NH C © 2006 Thomson Learning, Inc. All rights reserved H3 C O The rep eating unit of h yalu ronic acid 20-40 20 Acidic Polysaccharides • Heparin: a heterogeneous mixture of variably sulfonated polysaccharide chains, ranging in molecular weight from 6,000 to 30,000 g/mol. © 2006 Thomson Learning, Inc. All rights reserved 20-41 20 Acidic Polysaccharides • 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. • It binds strongly to antithrombin III, a plasma protein involved in terminating the clotting process. © 2006 Thomson Learning, Inc. All rights reserved 20-42 20 Carbohydrates End Chapter 20 © 2006 Thomson Learning, Inc. All rights reserved 20-43