Chem 161
Dec. 05, 2006
i) Isomers of monosaccharide:
Enantiomers
H
O
H
HO
H
R
H
H2C
H
OH
H
OH
OH
D-sugar
OH
O
HO
H
HO
S
HO
H2C
D-glucose
aldohexose
H
H
OH
H
H
HO
HO
H
H
H2C
OH
L-glucose
HO
O
CH2
O
HO
H
H
OH
H
OH
H2C
OH
H
H
OH
OH
OH
D-fructose
ketohexose
D-mannose
Diastereomers
ii) Hemiacetal formation:
O
C
O H
R
! !
C O
!
R O
H
!
H
C
OH
O
R
hemiacetal
O
H
HO
H
R
H
H2C
OH
OH
H
OH
OH
OH
H
O
HO
HO
O
OH
H
OH
HO
HO
H
O
hemiacetal
O
OH
OH
OH
OH
HO
HO
OH
OH
HO
HO
the two groups are
trans, so !-isomer
O
H
OH
OH
!-D-glucopyranose
OH
HO
HO
the two groups are
cis, so "-isomer
O
OH
OH
H
"-D-glucopyranose
* in the above case, the hemiacetal formation could give both isomers (α and β),
depending on which face of the carbonyl is attacked. Usually α favoured (anomeric
effect)
iii) Acetal formation:
C O
OH
C O
R O
H
R' OH
H, !
R'
O
C O
R
R
an acetal
( has two -OR groups)
hemiacetal
( has one -OH
and one -OR group)
eg. a)
O
H3C OH
HO
H
H
H O
O CH3
H
O CH3
elimination
rxn
addition
rxn
O
CH3
H
H O
oxonium ion
H3C O
H
addition
rxn
O CH3
H3C O
H3C OH
H
O
CH3
acetal
b)
OH
HO
HO
hemiacetal
O
OH
HO
HO
OH
OH
OH
O
O
OH
HO
HO
HO CH3
H
OCH3
(mixture of both
! and " isomers)
OH
HO
HO
OH
acetal
O
OH
OH
H
O CH3
!-D-glucoside
HO
HO
O
OH
O CH3
H
"-D-glucoside
iv) Classification:
Reducing sugars:
Non-reducing sugars
H
O
- all other sugars
aldehyde
- acetal
O
OH
OH
R
O
O R
a hydroxy ketone
hemiacetal
O R
v) Taste and Sweetness:
Two of the sweetest sugars (monosaccharide)
OH
HO
HO
HO
OH
HO
H
O
O
H
HO
OH
OH
OH
!-D-glucose (pyranose)
pyranose = 6 ring sugar
H
D-fructose (furanose)
furanose = 5 ring sugar
vi) Polymers of Sugars:
- polysaccharides ~ oligosaccharides (small polymers of sugars)
- 2 sugar units = disaccharide
- 3 sugar units = disaccharide
etc….!
- Sucrose – disaccharides (glucose + fructose)
OH
HO
O
HO
HO
!
"
OH
O
HO
OH
O
OH
D-fructose
D-glucose
α-D-glucopyranosyl-β-D-fructofuranoside
some more examples of sweet compounds:
Cl
OH
O
Cl
O
!
"
HO
OH
H O
N
S O
O
O
HO
O
Na
O
S
NH
Cl
O
O
OH
Sucralase = splenda
600x sweeter than sucrose
Sodium cyclamate
Saccharin
HO
H
N
H2N
O
O
Aspartame
 sugar polymers:
- Cellulose (cotton, paper)
- Starch (linear chain is amylose, branched network of polymer is glycogen)
O
Amylose, a component of starch has linear α-1,4 linkages as shown above; amylopectin
in starch has additional α-1,6 linkages crosslinking the chains into sheets, as does
glycogen – see pages 1108 and 1109 of Solomons’ Organic Chemistry text