Building Blocks of Life

Most Important Chemical Consideration of Sugars

Consider the anomeric carbon! The aldehyde on the oneposition can be nucleophilically attacked by any of the hydroxyls!

Hemiacetalization Concept Key to Carbohydrate Ring Structures

Nomenclature of Carbohydrates • D, L Defines the configuration at C5

D has the OH at Right in Fischer projectionL has the OH at Left in Fischer projection

• Gluco defines the configuration of the OH at C2, C4, C5. These OH’s are on same side while the C3-OH is opposite to others

• α,β defines the configuration of the OH at C1, the anomeric carbon

• Pyran indicates 6 member ring size• Furan indicates 5 member ring size

Examples follow

In Glucuronic acid C2, C4, C5 OH’s are on same side

C

CO2H

H

O

OHH

C

CO2H

H

O

OHH

OH

H

OHH

HO

H OH

H

H

H

HO

HO

glucuronic acid galacturonic acid

Alditols• In Mannitol C2, C4,

C5 OH’s are not at same side in Fisher Projection

CH2OH

CH2OH

H

H

OH

OH

H

H

HO

HO

Mannitol

CH2OH

OH

OH

H

CH2OH

H

HO

H

Xylitol

Conformations

O

OH

OH

OHOH

CH2OH

-D glucopyranose

O

OH

OH

OH

OHCH2OH

-D glucopyranose

[a]25D

+19o +112o

Anomers

For aged solutions [a] 25D

= +52.7o

Rotations of Fresh Solutions

Reason: Mutarotation is the best evidence for the cyclic hemiacetal structure of D-(+)-glucose

Monosaccharides,Hemiacetal Formation II

C

C

C

O H

CH2OH

C

C O

H

..HH

H

H

OH

OH

HO

OHC

C

C

O

CH2OH

C

C

HH

H

H

OH

OH

HO H

O

C

C C

C

HC HHO

CH2OH

O

H

OHH

H OH H

.. O

C

C C

C

C HHO

CH2OH

OHH

H OH H

OH

H

C5 OH attacks aldehyde giving a pyranose ring (6 member structure)

C4 OH attacks aldehyde giving a furanose ring (5 member structure)

O

OH

OH

OHOH

CH2OHO

O

OH

OH

OH

OHCH2OH

CHO

OHOH

OH

OH

CH2OH

OH

OHOH

HOCH2OH

O

OH

OH

OHHOCH2OH

CHO

H OH

HO H

H OH

H OH

CH2OH

CHOOH

OH

OH

D glucose

OH

-D glucopyranose

CH2OH

-D glucofuranose

Mutarotation

-D glucofuranose

-D glucopyranose

Ring closure between C1 and C4 -OH

Ring closure between C1 and C5 -OH

Hemiacetalization Concept Key to Carbohydrate Ring Structures

• Oligosaccharides – consist of several monosaccharide residues

joined together with glycosidic linkages

– di, tri, tetrasaccharides (depending on the number of monosaccharides)

– up to 10 - 20 monosaccharides (depending on analytical techniques i.e GC vs LC/MS)

• Polysaccharides – refer to polymers composed of a large number of

monosaccharides linked by glycosidic linkages

ex. Cellulose

oxygen bridge (ether-type orglycosidic bond)

anhydro-glucopyranose unit

Cellobiose

n = 1 -5000

OHOH

HO

CH2OHOO

CH2OH

HOOH

OOH

HOHO

CH2OHO

OOH

OHO

CH2OHO

Cellulose

b-D-anhydroglucopyranose units linked by (1,4)-glycosidic bonds

O O

O OO

OO

OH

CH2OH

HOHO

HOOH

CH2OHHO

OH

CH2OH

CH2OH

OHOH

HO

3'

4'n

1

2

3

4

5

6

2'5'

6'

1'

(potential aldehyde)

Non-ReducingEnd-Group

ReducingEnd-Group

PolysaccharidesPolysaccharides are polymers composed of

many monosaccharide units linked by glycosidic bonds

The glycosidic bond can can have either the α or a β-configuration and be joined to any of the hydroxyl groups at C-2, C-3, C-4 or C-6

The chain can either be Linear or Branched– branches can be single monosaccharide units,

chains of two or more units, or chains of a variable number of units

PolysaccharidesPolysaccharides can be divided into two classes

– Homopolysaccharides• consist of only one kind of monosaccharide

ex cellulose

– Heteropolysaccharides• consist of two or more kinds of

monosaccharides

ex galactoglucomannans

HomopolysaccharidesHomopolysaccharides can be further divided by the type(s) of glycosidic linkages

Homolinkages - either an α or a β configuration to a single position (exclusive of any branch linkages)

•that is a single kind of monosaccharide linked by one type of bond α-14, β-14, and so on

Heterolinkages - a mixture of a- and b-configurations and/or mixture of positions

•usually have a definite pattern for the arrangement of the linkages

HeteropolysaccharidesHeteropolysaccharides can have the same kind of linkage diversity as with homopolysaccharides, but now associated with one or more of the different kinds of monosaccharide units

– infinite degree of diversity of structure

Polysaccharides

Polysaccharides can not only have different sequences of monosaccharide units, but also different sequences of glycosidic linkages and different kinds of branching

– a very high degree of diversity for polysaccharides and their structure-function relationships

Plant PolysaccharidesThe conformation of individual monosaccharide residues in a polysaccharide is relatively fixed, however, joined by glycosidic linkages, they can rotate to give different chain conformations.

OOHO

HOO

OH

OHO

HOO

OH

HO OHO

HOO

OHOHO

HO O

OH

1,4 glycosidiclinkage 1,6 glycosidic

linkage

The different kinds of primary structures that result in secondary and tertiary structures give different kinds of properties

– water solubility, aggregation and crystallization, viscosity, gelation, etc.

Polysaccharides have a variety of functions– Storage of chemical energy in photosynthesis– Inducing Structural Integrity in plant cell walls

Plant Polysaccharides

StarchStarch is composed completely of D-glucose

– found in the leaves, stems, roots, seeds etc in higher plants

– stores the chemical energy produced by photosynthesis

Most starches are composed of two types of polysaccharides - amylose and amylopectin–amylose - a mixture of linear

polysaccharides of D-glucose units linked a-(1-4) to each other• between 250-5,000 glucose residues

The Components of Starch

O

HOO

OH

OH

O

HO

HO

OH

OHO

O

OH

OH

O

O

OHO

HO OH

O

(1-4)

Amylose

Amylopectin

– Amylopectin - a mixture of branched polysaccharides of D-glucose units linked a-(1-4), with ~ 5% a-(1-6) branch linkages• between 10,000-100,000 glucose residues

(1-4)

(1-6)O

HOO

OH

OH

O

HOO OH

OH

O

HOO

OH

OH

OHO

OH

OO

HOO OH

OH

O

O

HOO

HO

OH

O

Starch Polymer Components

Amylose

Amylopectin (1 residue in every 20 is 16 linked to branch off)

The Components of Starch

O

HOO

OH

OH

O

HO

HO

OH

OHO

O

OH

OH

O

O

OHO

HO OH

O

(1-4)

Amylose Amylopectin

(1-4)

(1-6)O

HOO

OH

OH

O

HOO OH

OH

O

HOO

OH

OH

OHO

OH

OO

HOO OH

OH

O

O

HOO

HO

OH

O

Starch tertiary structure (Helix)

Composition of Softwoods and Hardwoods

Cellulose42±2%

Hemicelluloses27 ± 2%Lignin

28 ± 3%Extractives 3 ± 2%

Softwood

Cellulose45 ± 2%

Hemicelluloses30 ± 5%Lignin

20 ± 4%Extractives 5 ± 3%

Hardwood