carbohydrate notes

CH 23 CARBOHYDRATES- carbohydrates are the most abundant molecules found in nature

- these complex multifunctional compounds exhibit classic organic chemical behavior in the execution of myriad important biological applications

CLASSIFICATION –

Original Definition % hydrate of carbon, Cn(H2O)m (a common molecular formula)

Modern Definition % a polyhydroxyaldehyde, a polyhydroxyketone or a compound which easily hydrolyzes to either of them

Saccharide, S % a sugar unit (from Latin for sweet)

Carbohydrate Hierarchy –

Monosaccharides & Disaccharides are commonly referred to as “simple sugars”

I. MONOSACCHARIDES –

- the structural characteristics of monosaccharides are fundamental to all carbohydrates

CLASSIFICATION –

- specific monosaccharides are usually referred to by their common names, but generalclassifications exist which are based on common structural features

A. Functional Group –

- every carbon in a monosaccharide is oxygenated (with a carbonyl =O or a hydroxyl -OH)

- monosaccharides can be classified according to the type of carbonyl group present:

PolysaccharideH

H2O, ΔOligosaccharide

H

H2O, Δ

H

H2O, ΔDisaccharide Monosaccharide

(polymer) (oligomer) (dimer) (monomer)

S Sn S S Sn S S S S

103 's units 10 - 102 's units 2 units 1 unit

B. Number of Carbons –

- monosaccharides can be classified according to the number of carbons present:

EX. classify according to FG & #C’s

C. D & L Configuration –

- all CHOH group carbons in monosaccharides are stereocenters (C*)

- the D/L configuration of all carbohydrates is based on the stereocenter contained in the simplealdotriose, glyceraldehyde

- all D-series sugars can be degraded to D-(+)-glyceraldehyde

- all L-series sugars can be degraded to L-(-)-glyceraldehyde

# C's =

Name =(Suffix)

3 4 5 6 7 ...........

triose tetrose pentose hexose heptose ............

CHO

CH2OHOHH

CHO

CH2OHHHO

D-(+)-glyceraldehyde L-(-)-glyceraldehyde

(R-configuration) (S-configuration)

CHOHCHO

CHOHCH2OH

CCH2OH

OCHOHCHOHCH2OH

an aldotetrose a 2-ketopentose

FFFFuuuunnnnccccttttiiiioooonnnnaaaallll GGGGrrrroooouuuupppp GGGGeeeennnneeeerrrraaaallll SSSSttttrrrruuuuccccttttuuuurrrraaaallll FFFFoooorrrrmmmmuuuullllaaaa NNNNaaaammmmeeee PPPPrrrreeeeffffiiiixxxx SSSSuuuuffffffffiiiixxxx

CH

RO

CR

RO

(Aldehyde)

(Ketone)

Aldose

Ketose

aldo-

keto-

-ose

-ose

(CHOH)n

CHO

CH2OH

CCH2OH

O(CHOH)n

CH2OH

Assigning the D/L Series Configuration –

- place the most oxidized carbon (C=O) closest to the “top” in a Fischer projection (FP)

- examine the configuration of the CHOH closest to the “bottom” (2nd to “last” C in the FP)

-OH Right %%%% D-Series -OH Left %%%% L-Series

EX ‘s

- most naturally occurring sugars are D-series

Family of D-Aldoses

(CHOH)n

CHO

CH2OHH OH

(CHOH)n

CHO

CH2OHHO H

(CHOH)n

C

CH2OHH OH

OCH2OH

(CHOH)n

C

CH2OHHO H

OCH2OH

D-aldoses L-aldoses D-ketoses L-ketoses

CH2OHH OH

OHHHHO

H OHCHO

HHOHO H

H OHHHO

CHO

CH2OH

C

CH2OHH OH

OHHHHOO

CH2OH

C

CH2OHHO H

HHOOHHO

CH2OH

D-(+)-glucose L-(-)-glucose D-(-)-fructose L-(+)-fructose

EPIMERS –

- a pair of sugars which differ in configuration at one asymmetric carbon (CCCC*) only

- while the unique configuration can exist at any stereocenter, the most common class of epimersdiffer in configuration at C-2 (in which case the carbon’s number may be understood & omitted)

- epimers are a class of diastereomers (stereoisomers which are not mirror image enantiomers)

- the arrows in the family of D-aldoses (shown on previous page) relate pairs of C-2 epimers

Other EX ‘s

CYCLIC STRUCTURES OF MONOSACCHARIDES –

- recall that the intramolecular addition reaction of a ( or *-hydroxycarbonyl compound results inthe formation of a cyclic hemiacetal

- monosaccharides exist predominately (>99%) in this more stable cyclic hemiacetal form

- aldohexoses form six-membered ring hemiacetals, while aldopentoses & ketohexoses form five-membered ring hemiacetals

CH2OHOHHOHH

H OHCHO

5

4

3

2

1

CH2OHOHHHHO

H OHCHO

5

4

3

2

1

CH2OHH OH

OHHHHO

HO HCHO

6

5

4

3

2

1

CH2OHH OH

HHOHHO

HO HCHO

6

5

4

3

2

1

D-ribose D-xylose D-mannose D-talosealdopentoses which are CCCC----3333 eeeeppppiiiimmmmeeeerrrrssss aldohexoses which are CCCC----4444 eeeeppppiiiimmmmeeeerrrrssss

(C)n

C

O

O

H(C)n

C

O

OH

hydroxy aldehyde or

hydroxy ketone

cyclic hemiacetal

n = 3 or 4ring = 5 or 6 member

OOH

OHHO

HO

OHO R

OH

OHHO

HO

R = H or CH2OH

aldopentoses & ketohexosesaldohexoses

EX. D-(+)-Glucose % an aldohexose which forms a six-membered ring hemiacetal

EX. D-(-)-Fructose % an ketohexose which forms a five-membered ring hemiacetal

Drawing Haworth Projection Formulas –

Six-Membered Ring Hemiacetals –

- draw a flat cyclohexane with hemiacetal ring oxygen in the upper right corner

- the hemiacetal carbon is on the right side of the ring @ C-1

- number the ring clockwise from C-1 to C-5

- C-6 is the -CH2OH group which points up in a D-sugar & down in an L-sugar

- the configurations @ C-2,C-3 & C-4 are determined from the following correlation:

Fischer Projection Haworth Projection

-OH Right -OH Down

-OH Left -OH Up

- the configuration @ C-1 is indeterminate (-OH can be either up or down)

O5

4

3 2

1

OCH2OH6

5

4

3 2

1

EX. D-(+)- Galactose

Five-Membered Ring Hemiacetals –

- draw a flat cyclopentane (pointing “back”) with hemiacetal ring oxygen in the center

- the hemiacetal carbon is on the right side of the ring:

@ C-1 in aldopentoses or @ C-2 in ketohexoses (C-1 is a -CH2OH)

- number the ring clockwise from C-1 to C-4 (aldopentoses) or C-2 to C-5 (ketohexoses)

- C-5 or C-6 is the -CH2OH group which points up in a D-sugar & down in an L-sugar

- the configurations @ C-2 & C-3 (aldopentoses) or @ C-3 & C-4 (ketohexoses) are determinedfrom the following correlation:


-OH Right -OH Down

-OH Left -OH Up

- the configuration @ C-1 (aldopentoses) or @ C-2 (ketohexoses) is indeterminate (-OH can beeither up or down)

EX. D-(-)- Ribose % an aldopentose

OHOCH2

5

4

3 2

1O

HOCH2

CH2OH

6

5

4 3

2 1

aldopentoses 2-ketohexoses

O

CH2OHOHHOHH

H OHCHO1

2

3

4

5

H2O


O OH

HOHHO

HOH

H H 1

23

4

5

+/or

CH2OHH OH

HHOHHO

H OHCHO

6

5

4

3

2

1

H2OO OH

HH

OH

OH

H

HO

H

OH

H1

23

4

5

6

+/or


EX. D-(-)- Fructose % a 2-ketohexose

Conformations of Six-Membered Ring Hemiacetals –

- the most stable cyclic hemiacetal form for aldohexoses is the chair conformer

Drawing Chair Conformers for Aldohexoses –

- arrange a chair with the hemiacetal carbon (C-1) pointing down on the right

- place the hemiacetal oxygen in the upper right position

- number the ring clockwise from C-1 to C-5

- C-6 is the -CH2OH group which points up in a D-sugar & down in an L-sugar

- the configurations @ C-2, C-3 & C-4 are determined from the following correlation:

Fischer Projection Haworth Projection Chair Conformer

-OH Right -OH Down -OH Down

-OH Left -OH Up -OH Up

- the configuration @ C-1 is indeterminate (-OH can be either up or down)

- the most stable aldohexose chair conformations will have the most equatorial -OH’s

EX. D-(+)- Glucose

H2O


O

OHHHO

HOH H HO OH

1

2

34

5

6

+/or

CH2OHOHHOHH

HO HC O

CH2OH1

2

3

4

5

6

OHOCH2

6

54

32 1

CH2OHH OH

OHHHHO

H OHCHO

6

5

4

3

2

1

H2OO OH

HH

OH

OH

H

H

HO

OH

H1

23

4

5

6

+/or


O

HOH

H

HO

H

H

HOH

OH

OH65

4

32

1

Chair Conformer

+/or

Anomers –

- diastereomers resulting from the indeterminate configuration at the hemiacetal carbon (C-1 orC-2) where the -OH can point either up or down

Anomeric Carbon –

- the original carbonyl carbon (C=O) which reacts & becomes the cyclic hemiacetal carbon

- this position is C-1 in aldopentoses & aldohexoses and C-2 in ketohexoses

- it is the only carbon in the ring with two oxygens attached

- anomers are also a class of epimers (diastereomeric sugars with identical configurations at everystereocenter except one)

- anomers are distinguished as follows:

Name Configuration @ Anomeric Carbon

"-Anomer (Alpha) -OH Down

$-Anomer (Beta) -OH Up

Mutarotation –

- because anomers are diastereomers, they have unique physical properties

- therefore, the specific rotation ["] values for anomers will be different

- placing either the "-anomer or the $-anomer in solution results in a “drift” of the specific rotationvalue ["] to a mutual value between the values of the two anomers

- the phenomenon of mutarotation is the result of an equilibrium which exists between the "-anomer & the $-anomer in solution:

"-anomer º “open-chain” carbonyl º $-anomer

- for aldohexoses, the mutarotation value is always closer to the value for the $$$$-anomer

- this indicates that the equilibrium mixture contains more of the more stable $$$$-anomer

- the $-anomer is more stable because the -OH on the anomeric carbon (C-1) is up & equatorial

CO

O

R

H

O

OH

H

54

32

1

β-Anomer

up & eeeeqqqquuuuaaaattttoooorrrriiiiaaaallll(more stable)

O

H

OH

12

3

45

α-Anomer

down & axial(less stable)

EX. D-(+)- Mannose

- after equilibrium has been established, the mutarotation value for D-(+)-mannose is:

["]eq = +60o (closer to the specific rotation value for the $-anomer)

Naming Cyclic Monosaccharides –

- sugars are classified and named according to hemiacetal ring size:

Pyranoses –

- six-membered ring hemiacetals (from pyran, a six-membered oxygen heterocycle)

- pyranoses are the cyclic derivations of aldohexoses:

Furanoses –

- five-membered ring hemiacetals (from furan, a five-membered oxygen heterocycle)

- furanoses are the cyclic derivations of aldopentoses & ketohexoses:

- the complete name of a specific monosaccharide in its cyclic hemiacetal form would include theprefix of that sugar’s name:

<" or $> - <D or L> - <sugar name prefix> - <pyran or furan> - ose

H2OO H

OHHO

H

OH

H

H

HO

OH

H

6

5

4

3 2

1H2O O OH

HHO

H

OH

H

H

HO

OH

H

6

5

4

3 2

1

CH2OHH OH

OHHHHO

HO HCHO1

2

3

4

5

6

α-D-Mannose β-D-Mannose"Open-chain"

[α] = +150o [α] = +23o(less than 1%)

OPyran

(CHOH)4

CHO

CH2OH

H2O OOH

OHHO

HO

OH

aldohexose pyranose

OFuran

O R

OH

OHHO

HO

R = H or CH2OH(CHOH)3

CHO

CH2OH

H2O

aldopentose furanose

CCH2OH

O(CHOH)3

CH2OH

ketohexose

or

EX ‘s

- students are responsible for knowing the structural formulas of the following monosaccharides:

D-(+)-Glyceraldehyde (an aldotriose)

D-(-)-Ribose (an aldopentose)

D-(+)-Glucose (an aldohexose)

D-(+)-Galactose (an aldohexose)

D-(+)-Mannose (an aldohexose)

D-(-)-Fructose (an ketohexose)

- only the Fischer projection formulas require memorization – the Haworth projection & chairconformer structural formulas are derived from the Fischer projection’s pattern of -OH’s

- note that there is no correlation between D/L (a drawing convention) & +/- (a physical property)

- students are only responsible for D & L structure (+ & - may be ignored)

REACTIONS OF MONOSACCHARIDES –

- because they are multifunctional compounds, monosaccharides exhibit the chemical behavior ofthree unique functional groups – carbonyls, alcohols & hemiacetals

- the small amount of “open-chain” carbonyl form present in the equilibrium accounts for thealdehyde/ketone reactions of monosaccharides

A. Epimerization –

- a base-catalyzed process where the acidic alpha-hydrogen ("-H) is removed & replaced, causingthe configuration at the alpha-carbon ("-C) to be racemized (creates epimers)

O H

OHH

OH

OH

H

HO

H

OH

H

6

5

4

3 2

1

α-D-galactopyranose β-D-fructofuranose

O

HHO

HOH H HO

OHOH

6

5

4 3

21

O H

OHOHHO

HOH

H H

5

4

3 2

1

α-D-ribofuranose

O

HOH

H

HO

H

H

HOH

OH

OH

12

3

45

6

β-D-glucopyranose

C O

C OHHα

C O

C HHOα

B

aldose or ketose aldose or ketose

B = OH , NH3, RNH2, R2NH, R3N,....

Mechanism –

EX.

B. Enediol Rearrangement –

- a base-catalyzed process where the carbonyl group migrates along the carbon chain

- note that aldoses & ketoses can thus interconvert under basic conditions

Mechanism –

CH2OHOHHOHH

H OHCHO

5

4

3

2

1

OH

CH2OHOHHOHH

HO HCHO1

2

3

4

5

D-ribose D-arabinose

C O

CHOH

CHOH

C O

B

aldose or ketose ketose or aldose

B = OH , NH3, RNH2, R2NH, R3N,....

EX.

- under basic conditions, monosaccharides will undergo both epimerization & enediolrearrangement, resulting in complex product mixtures

- therefore, contact with alkaline reagents is mostly avoided

C. Reduction –

- the small amount of “open-chain” carbonyl form present in the equilibrium allows for conversionof the carbonyl to an alcohol

EX.

D. Oxidation –

- different oxidizing agents produce different sugar derivatives:

1) Bromine Water, Br2/H2O

- only the aldehyde group of an aldose reacts:

CH2OHOHHOHH

H OHCHO1

2

3

4

5

OH C

CH2OHOHHOHH

CH2OHO

5

4

3

2

1

D-ribose D-ribulose

CH2OHH OH

HHOHHO

H OHCHO1

2

3

4

5

6

NaBH4

CH2OHH OH

HHOHHO

H OHCH2OH

6

5

4

3

2

1

D-galactose D-galactitol (Dulcitol)

(CHOH)n

CHO

CH2OH

aldose

CCH2OH

O(CHOH)n

CH2OH

ketose

or (CHOH)n

CH2OH

CH2OH

alditol

RARA = NaBH4, H2/Ni, ........

(CHOH)n

CHO

CH2OH

aldose

(CHOH)n

COOH

CH2OH

aldonic acid

Br2

H2O

- ketoses do not react:

EX.

2) Nitric Acid, HNO3

- both the aldehyde & primary alcohol groups of an aldose are oxidized:

- ketoses also react, giving more complex product mixtures:

EX.

CCH2OH

O(CHOH)n

CH2OH

ketose

Br2

H2ONR

CH2OHH OH

OHHHHO

H OHCHO

6

5

4

3

2

1

Br2

CH2OHH OH

OHHHHO

H OHCOOH1

2

3

4

5

6

D-glucose D-gluconic acid

H2O

(CHOH)n

CHO

CH2OH

aldose

(CHOH)n

COOH

COOH

aldaric acid

HNO3

CH2OHH OH

OHHHHO

HO HCHO1

2

3

4

5

6COOH

H OHOHHHHO

HO HCOOH

6

5

4

3

2

1

D-mannose D-mannaric acid

HNO3

CCH2OH

O(CHOH)n

CH2OH

ketose

(CHOH)n-1

COOH

COOH

aldaric acid

HNO3+ other products

3) Tollen’s Reagent, Ag(NH3)2+

- Tollen’s reagent provides a simple visible chemical test for aldehydes (a silver mirror is producedupon oxidation indicating a “positive test”)

- other oxidizing agents, such as Fehling’s & Benedict’s solutions (copper(II) complexes) producesimilar observable results with aldehydes (a red precipitate indicates a positive test)

- all of these reagents are strongly basic, and therefore cause epimerization & enediolrearrangement to occur with monosaccharides, resulting in complex product mixtures

- since enediol rearrangement converts ketoses to aldoses, ketoses are also ultimately oxidized& give positive tests, making them indistinguishable from aldoses:

- while Tollen’s reagent may not be useful for distinguishing aldoses from ketoses, it is useful foridentifying a certain class of carbohydrates:

Reducing Sugars, RS –

- sugars which reduce Tollen’s reagent (& related OA’s), becoming oxidized themselves

- include all aldoses & ketoses (which equilibrate in the cyclic hemiacetal form)

- exist as anomers & exhibit mutarotation

E. Ester Formation –

- all hydroxy groups in the monosaccharide react (like alcohols) with acid derivatives to produceester groups

(CHOH)n

CHO

CH2OH

aldose

CCH2OH

O(CHOH)n

CH2OH

ketose

oooorrrr (CHOH)n

COOH

CH2OH

aldonic acid

+ other products Ag(NH3)2

α-anomer β-anomer

R(OH)n + Ac2O R(OAc)n + AcOH

R(OH)n = sugar, aaaallllllll OH's react, including hemiacetal OH

Ac = C

O

CH3 (acetyl group); other acyl groups possible

Py

Py = N

(pyridine); other bases possible

(acetic anhydride); other acid derivatives possibleCH3 C

O

O C

O

CH3Ac2O =

EX.

E. Ether Formation –

- all hydroxy groups in the monosaccharide react (like alcohols) with alkyl halides to produce ethergroups

EX.

F. Osazone Formation –

- recall the reaction of carbonyls with hydrazines to produce hydrazones:

- the first two carbons of both aldoses & ketoses react with phenylhydrazine to form a bis-hydrazone known as an osazone

- hydrazone formation at the first carbonyl group is followed by oxidation of the "-carbon’s hydroxylgroup to a second carbonyl group which then forms the second hydrazone:

O OH

HH

OH

OH

H

H

HO

OH

H1

23

4

5

6

Ac2O

Py

O OAc

HH

OAcH

H

AcO

OAc

HOAc

6

5

4

3 2

1

O OH

HH

OH

OH

H

H

HO

OH

H

6

5

4

3 2

1CH3I

Ag2O

O OCH3

HH

OCH3H

H

CH3O

OCH3

HOCH3 1

23

4

5

6

C O + + H2OH

H2N NH C N NH

R(OH)n + CH3I R(OCH3)n + AgI

R(OH)n = sugar, aaaallllllll OH's react, including hemiacetal OH

Ag2O

Ag2O (Silver oxide) most common base; others possible

CH3 (Methyl) most common alkyl group; others possible

I (Iodo) most common leaving group; others possible

- any difference at C-1 or C-2 is lost in the formation of osazones

- thus, C-2 epimers will form the same osazones (as will related aldoses & ketoses)

EX.

G. Glycoside Formation –

- recall that Tollen’s reagent (& related OA’s) identify reducing sugars

- this distinguishes them from nonreducing sugars which do not give positive Tollen’s tests

- this distinction is the result of the different functional groups present in these two cyclicmonosaccharide classes:

- the reducing sugar has a hemiacetal group which opens in water

- the nonreducing sugar has an acetal group which does not open in water:

CH2OHH OH

OHHHHO

HO HCHO1

2

3

4

5

6

D-mannose

CH2OHH OH

OHHHHO

H OHCHO

6

5

4

3

2

1

D-glucose

CH2OHOHHOHH

HO HC O

CH2OH1

2

3

4

5

6

D-fructose

H

same osazone

Ph =

NH NH23 Ph

H

NH NH23 Ph

CH NC N

NHNH

PhPh

HHOH OH

OHHCH2OH

1

2

3

4

5

6

NH NH23 Ph H

CH OCH OH

(CHOH)n

CH2OH

CCH2

O(CHOH)n

CH2OH

OH

aldose

ketose

3 NH NH2+oooorrrrH

phenylhydrazine

CH NC N

(CHOH)n

CH2OH

NHNH

PhPh

osazone

+

NH2

+ NH3

Ph =

- Glycosides are cyclic acetal forms of sugars

- they are prepared by the acid-catalyzed reaction of an alcohol with a pyranose or furanose

- note that only the anomeric (hemiacetal) carbon’s hydroxyl group reacts under these conditions

Naming Glycosides –

- place R group (alkyl or aryl) name in front (separate word)

- change ending from e Y ide

(C)n

C

O

O

H(C)n

C

O

OH

cyclic hemiacetal

H2O

open-chain carbonyl

OA(C)n

C

O

OH

O

H

oxidizes

(aldose or ketose) (gives + test)

OA = Ag(NH3)2 ,.......

therefore; rrrreeeedddduuuucccciiiinnnngggg sugars are hhhheeeemmmmiiiiaaaacccceeeettttaaaallllssss

cyclic acetal

H2O OA

does not oxidize

(glycoside) (does nnnnooootttt give + test)

OA = Ag(NH3)2 ,.......

therefore; nnnnoooonnnnrrrreeeedddduuuucccciiiinnnngggg sugars are aaaacccceeeettttaaaallllssss (glycosides)

NR

won't open in H2O

(C)n

C

O

OR

NR

(requires H )

OOR

ROHO

OH

OHHO

HO

OH

pyranose

H+O

OR

OHHO

HO

OH

H2O+

pyranoside

ROHH+ H2O+

furanoside

O R'

OH

OHHO

HO

R' = H or CH2OHfuranose

O R'

OR

OHHO

HO

ROH = CH3OH, CH3CH2OH, PhOH, another monosaccharide,.........

EX ‘s Preparation & naming of glycosides

- note the distinct contrast in chemical behavior between reducing & nonreducing sugars:

Nonreducing Sugars, NRS –

- sugars which do not reduce Tollen’s reagent (& related OA’s)

- are glycosides (cyclic acetals)

- do not equilibrate in water with the “open-chain” carbonyl form

- do not exhibit anomerism or mutarotation

II. DISACCHARIDES –

- sugars composed of two monosaccharides connected in glycoside (acetal) linkages

- the glycosidic bond is formed between the anomeric carbon of the “first” monosaccharide unit &the hydroxyl group of the “second” monosaccharide unit

- disaccharides can be categorized according to the position of the hydroxyl group on the “second”monosaccharide unit making up the glycoside:

OH Position on 2nd MS Unit Disaccharide Class

@ C-4 1÷4' Glycoside




methyl α-D-fructofuranoside

O

HOH

H

HO

H

H

HOH

OH

OH65

4

32

1

ethyl β-D-glucopyranoside

O

HHO

HOH H HO OCH3

OH6

5

4 3

2

1

O

HOCH2CH3

H

HO

H

H

HOH

OH

OH

12

3

45

6

OHCH3CH2H+ H2O+

β-D-glucopyranose

OHCH3H+

O

HHO

HOH H HO OH

OH1

2

34

5

6

α-D-fructofuranose

H2O+

α-anomer β-anomer

- disaccharides can be categorized according to the configuration at the anomeric carbon of the firstmonosaccharide unit:

“OR” Position on Anomeric C of 1st MS Unit Disaccharide Class

Up $-Glycoside (beta)

Down α-Glycoside (alpha)

- typical monosaccharide units found in naturally occurring disaccharides are glucose, galactose &fructose

A. 1÷÷÷÷4' Glycosides –

- these represent the most common naturally occurring disaccharides

- the anomeric carbon (C-1) of the first MS unit is connected through the C-4 OH of the secondMS unit

1) Maltose –

- this disaccharide is a hydrolysis product of starch:

- maltose can be described as: two glucose units in an αααα(1÷÷÷÷4') glycoside (glucoside)

Starch H

H2O, Δ

H

H2O, ΔMaltose 2 Glucose

MMMMaaaallllttttoooosssseeee

4-O-(α-D-glucopyranosyl)-β-D-glucopyranose

NRS Unit

RS Unit

α(1 4') glycoside

O

HHHO

H

H

HOH

OH

OH

O

HOH

H

HO

H

H

OH

OH

OH6'5'

4'

3'2'

1'

65

4

32

1

β shown; α possible+/or

2) Cellobiose –

- this disaccharide is a hydrolysis product of cellulose:

- cellobiose can be described as: two glucose units in a ββββ(1÷÷÷÷4') glycoside (glucoside)

3) Lactose –

- a naturally occurring disaccharide found in the milk of mammals such as cows & humans

- lactose yields galactose & glucose upon hydrolysis:

- lactose can be described as: galactose (nonreducing) & glucose (reducing) units in aββββ(1÷÷÷÷4') glycoside (galactoside)

Cellulose H

H2O, Δ

H

H2O, Δ2 GlucoseCellobiose

Lactose H

H2O, ΔGalactose + Glucose

LLLLaaaaccccttttoooosssseeee4-O-(β-D-galactopyranosyl)-β-D-glucopyranose

NRS Unit

β(1 4') glycoside

O

HOHO

H

OH

HH

OH

OH

H

O

HOH

H

HO

H

HH

OH

OH

1'2'

3'

4'5'

6'6

54

32

1

RS Unit(galactose) (glucose)

β shown; α possible+/or

α shown; β possible+/or

CCCCeeeelllllllloooobbbbiiiioooosssseeee

4-O-(β-D-glucopyranosyl)-α-D-glucopyranose

NRS Unit

β(1 4') glycoside

O

HOHO

H

H

HOH

OH

OH

H

O

HH

OH

HO

H

HH

OH

OH

1'2'

3'

4'5'

6'6

54

32

1

RS Unit

B. 1÷÷÷÷6' Glycosides –

- the anomeric carbon (C-1) of the first MS unit is connected through the C-6 OH of the secondMS unit

Gentiobiose –

- this disaccharide is incorporated into crocin, the principle component of saffron

- gentiobiose can be described as: two glucose units in a ββββ(1÷÷÷÷6') glycoside (glucoside)

C. 1÷÷÷÷2' Glycosides –

- these compounds & their related 1÷1' glycosides represent the nonreducing disaccharides

- the glycosidic linkage involves the anomeric carbons from both monosaccharide units

Sucrose –

- a naturally occurring disaccharide found in sugar cane & sugar beets (table sugar)

- hydrolysis of sucrose yields glucose & fructose

- sucrose can be described two ways:

glucose & fructose units in an αααα(1÷÷÷÷2') glycoside (glucoside)

or; fructose & glucose units in a ββββ(2'÷÷÷÷1) glycoside (fructoside)

α shown; β possible+/or

GGGGeeeennnnttttiiiioooobbbbiiiioooosssseeee

6-O-(β-D-glucopyranosyl)-α-D-glucopyranose

NRS Unit

β(1 6') glycosideO

HOHO

H

H

HOH

OH

OH

H

O

HH

OH

HO

H

HH

OH

HO

6'

5'4'

3'2'

1'

65

4

32

1

RS Unit

Sucrose H

H2O, ΔGlucose + Fructose

H

H2O, Δ2 GlucoseGentiobiose

Naming Disaccharides –

- the following systematic nomenclature method is used for disaccharides:

1) identify the hydroxyl oxygen making the glycosidic bond as a number prefix followed by O

EX. 4-O- prefix indicates the RS unit’s C-4 OH makes the glycoside

2) name the NRS unit (left), changing the ending from ose ÷ osyl

3) name the RS unit (right) as a normal cyclic monosaccharide & indicate the anomer present

- students are not responsible for common names of disaccharides

EX.

III. POLYSACCHARIDES –

- macromolecules made up of long chains of monosaccharide units joined in glycosidic linkages

- the most common polysaccharides are polymers of glucose

SSSSuuuuccccrrrroooosssseeee

α-D-glucopyranosyl-β-D-fructofuranoside

NRS Unit (glucose)

α(1 2') glucoside

O

HHHO

H

H

HOH

OH

OH

OO

HHO

HOH H HO OH6'

5'

4' 3'

2'

1'

12

3

45

6

β-D-fructofuranosyl-α-D-glucopyranoside

NRS Unit (fructose)

or

β(2' 1) fructoside

LLLLaaaaccccttttoooosssseeee4-O-(β-D-galactopyranosyl)-α-D-glucopyranose

O

HOHO

H

OH

HH

OH

OH

H

O

HH

OH

HO

H

HH

OH

OH

12

3

45

66'

5'4'

3'2'

1'

A. Starch –

- the glucose (energy) storage form for plants

- starch contains two components, which are separable on the basis of water solubility

1) Amylose –

- a linear polymer of glucose units in α(1÷4') glycosides (glucosides)

2) Amylopectin –

- a branched polymer of glucose units in α(1÷4') glycosides with α(1÷6') glycoside branches

H

H

HHO

H

OH

OH

O

OH

O

H

HHHO

H

H

OH

O

OH

O

H

HHHO

H

H

OH

O

OH

O

H

HH

O

HO

H

H

OH

O

OHn

(

)AAAAmmmmyyyylllloooosssseeee

(n ~ 103 's)

α(1 4') glycoside

StarchH2O

soluble

insoluble

Amylose

Amylopectin

H2OH

H2OH

MaltoseH2OH Glucose

Maltose + IsomaltoseH2OH Glucose

20%

80%

H

H

HHO

H

OH

OH

O

OH

O

H

HHHO

H

H

OH

O

OH

O

H

HHHO

H

H

OH

O

O

H

HH

O

HO

H

H

OH

O

OH

H

HHHO

H

H

OH

O

OH

O

H

HH

O

HO

H

H

OH

O

OHO

n

(

)

AAAAmmmmyyyyllllooooppppeeeeccccttttiiiinnnn

(n ~ 104 total)

α(1 4') glycoside

α(1 6') glycoside branch

(n ~ 20 -25 between branches)

B. Glycogen –

- the glucose (energy) storage form for animals

- a branched polymer of glucose units in α(1÷4') glycosides with α(1÷6') glycoside branches

- so; same as amylopectin, but more highly branched

- the increased branching in glycogen provides more available glucose “ends” to satisfy the greatermetabolic demand of motile organisms

C. Cellulose –

- the principal component of plant cell walls, providing the plant’s structural strength & rigidity

- a linear polymer of glucose units in β(1÷4') glycosides (glucosides)

- most organisms cannot digest cellulose because they lack the enzyme which catalyzes thehydrolysis of the β−glucoside

H

HH

HO

H

H

OH

O

OH

O

H

H

OHO

H

OH

OH

O

OH

H

H

HO

H

HO

H

H

OH

O

OHH

HH

HO

H

H

OH

O

OH

O

( )n

CCCCeeeelllllllluuuulllloooosssseeee

(n ~ 103 's)

β(1 4') glycoside

H

H

HHO

H

OH

OH

O

OH

O

H

HHHO

H

H

OH

O

OH

O

H

HHHO

H

H

OH

O

O

H

HH

O

HO

H

H

OH

O

OH

H

HHHO

H

H

OH

O

OH

O

H

HH

O

HO

H

H

OH

O

OHO

n

(

)

GGGGllllyyyyccccooooggggeeeennnn

(n ~ 106 total)

α(1 4') glycoside

α(1 6') glycoside branch

(n ~ 10 -12 between branches)

carbohydrate notes

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