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Home , Fischer projection, Haworth projection, Octose

Organic Lecture Series CarbohydratesCarbohydrates

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CarbohydratesCarbohydrates Organic Lecture Series

•• :Carbohydrate: a polyhydroxyaldehyde, a polyhydroxyketone, or a compound that gives either of these compounds after hydrolysis

2 CarbohydratesCarbohydrates Organic Lecture Series •• :Monosaccharide: a carbohydrate that cannot be hydrolyzed to a simpler carbohydrate

– they have the general formula CnH2nOn, where n varies from 3 to 8 – : a monosaccharide containing an group – : a monosaccharide containing a group

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Organic Lecture Series MonosaccharidesMonosaccharides • are classified by their number of atoms

Name Formula C3 H6 O3 C4 H8 O4 C5 H10O5 C6 H12O6 C7 H14O7 Octose C8 H16O8 4 Organic Lecture Series MonosaccharidesMonosaccharides • There are only two

CHO CH2 OH CHOH C= O

H2COH CH2 OH CH2 OH D ihydroxyacetone HC OH (an aldotriose) (a ketotriose) H2C OH Glycerol 1,2,3-Propanetriol

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MonosaccharidesMonosaccharidesOrganic Lecture Series

CHO CH2 OH CHOH C= O

CH2 OH CH2 OH Glyceraldehyde (an aldotriose) (a ketotriose)

• Often the designations aldo- and keto- are omitted and these compounds are referred to simply as trioses, , and so forth – although these designations do not tell the nature of the carbonyl group, they at least tell the number of

6 Organic Lecture Series MonosaccharidesMonosaccharides • Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers

CH O CH O HOHC HO C H

CH 2 OH CH 2 OH (R)-Glyceraldehyde (S)-Glyceraldehyde

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Organic Lecture Series • Glyceraldehyde contains a stereocenter and exists as a pair of enantiomers CH O CH O HOHC HO C H

CH 2 OH CH 2 OH (R)-Glyceraldehyde (S)-Glyceraldeh yd e

HO CHO OHC OH

CH2OH CH2OH

8 Organic Lecture Series • : a two dimensional representation for showing the configuration of – horizontal lines represent bonds projecting forward – vertical lines represent bonds projecting to the rear – the only atom in the plane of the paper is the stereocenter

CHO convert to a CH O Fischer projection H C OH H OH

CH2 OH CH 2 OH

. (R)-Glyceraldehyde (R)-Glyceraldeh yd e (three-dimensional (Fischer projection) representation) 9

Organic Lecture Series D,L Monosaccharides

In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde (aldehyde is C1-at the top).

CH O CHO HOH HO H

CH 2 OH CH2 OH D-Glyceraldehyde L-Glyceraldehyde 25 25 [α]DD = +13.5 [α] = -13.5 -OH to Right -OH to Left 10 Organic Lecture Series • According to the conventions proposed by Fischer – D-monosaccharide: a monosaccharide that has the same configuration at its penultimate carbon as D-glyceraldehyde; that is, its -OH is on the right when written as a Fischer projection – L-monosaccharide: a monosaccharide that has the same configuration at its penultimate carbon as L-glyceraldehyde; that is, its -OH is on the left when written as a Fischer projection

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Organic Lecture Series

• Here are the two most abundant D-aldotetroses and the two most abundant D-aldopentoses • The configuration is assigned at the next to last C in the chain

CHO CHO CHO CHO H OH H H H OH HO H H OH H OH H OH H OH HOHOH H

CH2 OH CH2 OH CH2 OH CH2 OH D- D- D- 2-Deoxy-D- ribose

12 Organic Lecture Series

• And the three most abundant

CHO CHO CH OH 2 H OH H OH C O HO H HO H HO H H OH HO H H OH H OH H OH H OH CH OH CH OH CH OH 2 2 2 D- D- D-

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Organic Lecture Series Amino

• Amino : a sugar that contains an -NH2 group in place of an -OH group – only three amino sugars are common in nature – N-acetyl-D-glucosamine is a derivative of D- glucosamine

CHO CHO CH O CH O O 2 H NH2 H2 N H H NH2 H NHCCH3 HO H HO H HO H HO H H OH H OH HO 4 H H OH H OH H OH H OH H OH

CH2 OH CH2 OH CH 2 OH CH 2 OH D-Glucosamine D-Mannosamine D-Galactosamine N-Acetyl-D- glucosamine

14 Cyclic Structure Organic Lecture Series • Monosaccharides have hydroxyl and carbonyl groups in the same molecule and exist almost entirely as five- and six- membered cyclic hemiacetals – anomeric carbon: the new stereocenter created as a result of cyclic hemiacetal formation – : carbohydrates that differ in configuration at their anomeric carbons

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Organic Lecture Series Haworth Projections • Haworth projections

– five- and six- CH2OH membered H OH hemiacetals are OH O H Anomeric Carbon represented as planar pentagons or OH H hexagons, as the case H OH may be, viewed through the edge H – they are most HOH2C O commonly written with H H Anomeric Carbon the anomeric carbon H OH on the right and the OH OH hemiacetal oxygen to the back right 16 Organic Lecture Series α-D-Glucopyranose α-D-Glucose 6 CH2OH H 5 H OH O 4 H 1 Anomeric Carbon

2 OH 3 OH H OH

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Organic Lecture Series α-D-Ribofuranose α-D-Ribose

5 H CH2OH O 4 H H 1 Anomeric Carbon

H 3 2 OH OH OH

18 Organic Lecture Series • Haworth projections CH2OH the designation β- H H means that the - OH O OH on the H Anomeric Carbon anomeric carbon OH OH α is cis to the H OH

terminal -CH2OH; α- means that it is trans to the CH2OH β terminal -CH2OH H OH OH O H Anomeric Carbon

OH H H OH 19

Haworth Projections Organic Lecture Series

1 CHO redraw to show the -OH CH2 OH H OH on carbon-5 close to the 5 OH aldehyde on carbon-1 H HO H H O C OH H H OH HO 1 H Groups on the right side go H 5 OH down on the Haworth. H OH CH2 OH D-Glucose anomeric anomeric carbon carbon CH2 OH CH2 OH O H O OH(β) H H H + H OH H OH H HO H HO OH(α) H OH H OH β-D-Glucopyranose α-D-Glucopyranose (β-D-Glucose) ( α-D-Glucose) 20 Organic Lecture Series Haworth Projections – six-membered hemiacetal rings are shown by the infix -pyran-pyran – five-membered hemiacetal rings are shown by the infix -furan-furan

O O Furan Pyran

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Organic Lecture Series Conformational Formulas – five-membered rings are close to being planar that Haworth projections are adequate to represent

HOCH HOCH 2 O H 2 O OH ( β) H H HH H OH ( α) H H OH OH OH H α-D-Ribofuranose β-2-Deoxy-D-ribofuranose (α-D-Ribose) (β-2-Deoxy-D-ribose)

22 Organic Lecture Series

other monosaccharides also form five-membered cyclic hemiacetals here are the five-membered cyclic hemiacetals of D-fructose

1 CH 2 OH 1 2 C= O (β) HOCH2 O CH 2 OH 3 HOCH2 O OH 2 HO H 5 H HO 4 5 H HO 2 H OH H OH(α) H CH 2 OH H 5 OH 1 HO H 6 HO H CH 2 OH α-D-Fructofuranose D-Fructose β-D-Fructofuranose (α-D-Fructose) (β-D-Fructose)

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Organic Lecture Series

– for , the six-membered ring is more accurately represented as a chair conformation OH H OH H H O H OH HO HO HO OH HO O H OH H OH H H H H β-D-Glucopyranose rotate about (β-D-Glucose) C-1 to C-2 bond

H OH H OH H H O HO OH HO HO H HO H H OH H OH H O H OH α-D-Glucopyranose (α-D-Glucose)

24 Organic Lecture Series

– compare the orientations of groups on carbons 1-5 in the Haworth and chair projections of β-D-glucopyranose, in each case they are up-down-up-down-up respectively

6 CH OH All Groups axial 2 6 5 O H OH(β) 4 CH2 OH H HO O 4 OH H 1 HO 5 HO H 3 2 OH( β) 3 2 OH 1 H OH β-D-Glucopyranose β-D-Glucopyranose

() (chair conformation) 25

Organic Lecture Series • : the change in specific rotation that occurs when an α or β form of a carbohydrate is converted to an equilibrium mixture of the two

[α] after % Present at Mon os accharide [α] Mutarotation Equilibrium α-D-glucose +112.0 +52.7 36 β-D-glucose +18.7 +52.7 64 Slight preference for equatorial α-D-galactose +150.7 +80.2 28 β-D-galactose +52.8 +80.2 72

CH2 OH CH2 OH HO O HO O HO HO OH (β) OH HO OH (α) β-D -Glu cop yranose 25 α-D -Glucopyranose [α]D +18.7 25 26 [α]D +112 Organic Lecture Series • : a carbohydrate in which the - OH of the anomeric carbon is replaced by -OR – methyl β-D-glucopyranoside (methyl β-D- glucoside) CH2 OH CH2 OH CH2 OH O O H OH O OCH3 H H H + H H + CH OH H H + OH H 3 OH H OH H -H2 O HO H HO H HO OCH3 H OH H OH H OH β-D-Glucopyranose Methyl β-D-gluco- Methyl α-D-gluco- (β-D-Glucose) pyranoside pyranoside ( Methyl β-D-glucoside) (Methyl α-D-glucoside)

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Glycosides Organic Lecture Series • Glycosidic bond: the bond from the anomeric carbon of the glycoside to an - OR group • Glycosides are named by listing the name of the alkyl or aryl group bonded to oxygen followed by the name of the carbohydrate with the ending -e replaced by -ide – methyl β-D-glucopyranoside – methyl α-D-ribofuranoside

28 N-Glycosides Organic Lecture Series • The anomeric carbon of a cyclic hemiacetal also undergoes reaction with the N-H group of an amine to form an N-glycoside – N-glycosides of the purine and pyrimidine bases are structural units of nucleic acids

H N N N

N N N

Pyrimidine Purine

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Organic Lecture Series

N

N Pyrimidine

O NH2 O CH HN N HN 3 O N O N O N H H H Uracil Cy to sine Thymine

30 Organic Lecture Series H N N

N N Purine

NH2 O N N HN N N N N H2 N N H H Adenine Guanine 31

Organic Lecture Series N-Glycosides – the β-N-glycoside formed between D- ribofuranose and cytosine

NH2 N a β-N-glycosidic bond O N HOCH2 O H H H H anomeric HO OH carbon

32 Reduction to Organic Lecture Series Alditols • The carbonyl group of a monosaccharide can be reduced to an hydroxyl group by a variety of reducing agents, including NaBH4 and H2/M (metal catalyst)

CHO CH2 OH H OH H OH CH2 OH HO O HO H HO H HO NaBH4 OH H OH H OH OH H OH H OH

β-D-Glucopyranose CH2 OH CH2 OH D-Glucose D-Glucitol (D-Sorbitol)

“Sugar alcohol” additive 33

Organic Lecture Series

other alditols which are naturally occurring

CH2 OH HO H CH 2 OH

CH2 OH HO H H OH H OH H OH HO H H OH H OH H OH

CH2 OH CH2 OH CH 2 OH Eryth ri to l D-Mannitol Xylitol

34 Organic Lecture Series Oxidation to Aldonic Acids • The -CHO group can be oxidized to -COOH

O H O O- C C CH 2 OH H OH oxidizing H OH HO O HO H agent HO H HO H OH H OH OH basic OH H OH solution H OH

CH2 OH CH2 OH β-D-Glucopyranose D-Glucose D-Gluconate (β-D-Glucose)

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Organic Lecture Series Oxidation to Aldonic Acids 2- are also oxidized to aldonic acids under the conditions of the oxidation, 2-ketoses equilibrate with isomeric

CHOH CHO CH2 OH C= O C-OH CHOH (CHOH) ( CHOH) (CHOH)n n n CH2 OH CH2 OH CH2 OH A 2-ketose An enediol An aldose

At first glance-this appears to be a transposition of a carbonyl group 36 Organic Lecture Series Oxidation to Uronic Acids • Enzyme-catalyzed oxidation of the terminal -OH group gives a -COOH group

CHO CHO OH H OH H OH CO2H H O H OH enzyme H OH H H H HO H HO H H OH H OH H OH OH OH

CH2OH COOH

D-Glucuronic acid

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Organic Lecture Series Oxidation to Uronic – in humans, D-gluconic acid is an important component of theAcids acidic of connective tissue – it is also used by the body to detoxify foreign hydroxyl-containing compounds, such as phenols and alcohols; one example is the intravenous anesthetic propofol

COO- HO O HO HO O OH

Propofol A urine-soluble glucuronide 38 Organic Lecture Series Oxidation by HIO4 • Periodic acid cleaves the C-C bond of a glycol

OH HO C OH O -H2 O + I COH HO OH OH

A 1,2-diol Periodic acid

OH CO O C O I + H3 IO4 CO OH C O OH Iodic acid

A cyclic periodic ester 39

Organic Lecture Series Oxidation by HIO4 – it also cleaves α-hydroxyketones:

H H H H COH H C OH H CO + H5 IO6 H2 O C O HO C OH HO CO R R R α-Hydroxyketone Hydrated intermediate – and α-hydroxyaldehydes: O OH OH H C H COH HOC + H O H5 IO6 H C OH 2 H C OH R R H C O R α-Hydroxyaldehyde Hydrated intermediate 40 Organic Lecture Series Glucose Assay • The analytical procedure most often performed in the clinical laboratory is the determination of glucose in blood, urine, or other biological fluid – this need stems from the high incidence of diabetes in the population

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Organic Lecture Series Glucose Assay • The glucose oxidase method is completely specific for D-glucose

COOH H OH CH2 OH glucose HO O oxidase HO H + + HO O2 + H2 O H OH H2 O2 OH OH H OH

β-D-Glucopyranose CH 2 OH (β-D-Glucose) D-Gluconic acid

42 Glucose Assay Organic Lecture Series – the enzyme glucose oxidase is specific for β-D-glucose

– molecular oxygen, O2, used in this reaction is reduced to

peroxide H2O2

– the concentration of H2O2 is determined experimentally, and is proportional to the concentration of glucose in the sample

peroxidase o-toluidine + H2 O2 colored product + H2 O

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Glucose Assay Organic Lecture Series – in one procedure, hydrogen peroxide is used to oxidize o-toluidine to a colored product, whose concentration is determined spectrophotometrically

peroxidase o-toluidine + H2 O2 colored product + H2 O

44 Organic Lecture Series • Table sugar, obtained from the juice of sugar cane and sugar beet

a unit of α-D- CH2 OH CH2 OH O O glucopyranose 1 HO OH HO 1 HO OH α-1,2-glycosidic OH bond HOCH O HOCH O 2 O 2 O a unit of β-D- HO 2 HO 2 fructofuranose CH OH CH OH 1 2 1 2 HO HO

Glucose and Fructose 45

Organic Lecture Series • The principle sugar present in milk – about 5 - 8% in human milk, 4 - 5% in cow’s milk

CH2 OH 4 O OH CH 2 OH OH HO O O OH 1 OH β-1,4-glycosidic bond HO CH2 OH OH O CH OH 4 2 HO O O OH 1 HO OH OH

Glucose and Galactose 46 Organic Lecture Series • From malt, the juice of sprouted barley and other cereal grains

1 4 CH 2 OH O O HOCH2 OH O OH(β) OH HO HO OH CH2 OH O α-1,4-glycosidic bond HO Glucose and Glucose HO 1 CH OH (Glucose Dimer) OH 4 2 O O HO OH (β) OH 47

Organic Lecture Series

ImportantImportant CarbohydrateCarbohydrate PolymersPolymers 1.

2.

3.

48 Organic Lecture Series StarchStarch • Starch is used for energy storage in plants – it can be separated into two fractions; and ; each on complete hydrolysis gives only D-glucose – amylose is composed of continuous, unbranched chains of up to 4000 D-glucose units joined by α-1,4-glycosidic bonds – amylopectin is a highly branched polymer of D-glucose; chains consist of 24-30 units of D- glucose joined by α-1,4-glycosidic bonds and branches created by α-1,6-glycosidic bonds

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Organic Lecture Series

O OH

H O α-D-glucose polymer in a H α -1,4 linkage H 1 H H OH α HO O OH

H O H 4 H 1 H H OH OH HO O

H O H 4 H 1 H H OH HO O 50 Organic Lecture Series OHO

H O H H 1 H H OH α HO O α-D-glucose polymer in a OH 6 α -1,6 linkage CH2 H O H H 1 H H OH HO O OH 6 CH 2 H O H H H H OH 1 HO O 51

Organic Lecture Series CelluloseCellulose • Cellulose is a linear polymer of D- glucose units joined by β-1,4- glycosidic bonds – it has an average molecular weight of 400,000 g/mol, corresponding to approximately 2800 D-glucose units per molecule – both rayon and acetate rayon are made from chemically modified cellulose

52 Organic Lecture Series CelluloseCellulose

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Organic Lecture Series Glycogen Glycogen is the reserve carbohydrate for animals – glycogen is a nonlinear polymer of D- glucose units joined by α-1,4- and α-1,6- glycosidic bonds bonds – the total amount of glycogen in the body of a well-nourished adult is about 350 g (about 3/4 of a pound) divided almost equally between liver and muscle

54 Organic Lecture Series OHO

H O H H H H OH 1 Glycogen: HO O OH α -1,6 and 6 α -1,4 linkages CH2 H O H H H H OH 1 HO O OH

H O H 4 H H H OH 1

HO O 55

Organic Lecture Series

•Saccharin is about 300 times as sweet as sucrose, but has an unpleasant bitter or metallic aftertaste, especially at high concentrations. •Unlike the newer artificial sweetener aspartame, saccharin is stable when heated, even in the presence of acids, does not react chemically with other food ingredients, and stores well. 56 Organic Lecture Series

CH3

•Aspartame is the methyl ester of the dipeptide of the natural amino acids L-aspartic acid and L-phenylalanine. •Under strongly acidic or alkaline conditions, aspartame first generates methanol by hydrolysis. Under more severe conditions, the peptide bonds are also hydrolyzed, resulting in the free amino acids. 57

Organic Lecture Series

Sucralose-A Trichloro-Sucrose

Cl OH

H O H HO H H OH Cl

H O H O

H OH HO

H

Cl

58 Organic Lecture Series Comparison of Sucralose and Sucrose

H OH

H O HO HO H H OH OH

H O Cl OH H O

H H O OH H HO HO H H H OH Cl

H O OH H O

H OH HO

H

Cl 59

Organic Lecture Series Cl OH

H O H HO H H OH Cl

H O H O

H OH HO

H

Cl •Sucralose is approximately 600 times sweeter than sucrose (table sugar), twice as sweet as saccharin, and four times as sweet as aspartame. •Unlike aspartame, it is stable under heat and over a broad range of pH conditions and can be used in baking or in products that require a longer shelf life. •Since its introduction in 1999, sucralose has overtaken Equal in the $1.5 billion artificial sweetener market, holding a 62% market share 60