13.3 Cyclic Structures of Monosaccharides

1

Formation of cyclic hemiacetal or cyclic hemiketal.Most common ring sizes: 5 and 6 membered rings.

Cyclic hemiacetal

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O OOH OH

R

Cyclic hemiketal

Intramolecular Addition of OH to an Aldehyde or Ketone

2

The mechanism is the same as nucleophilic addition of OH to –CHO in acidic condition.

CHO

OHH

HHO

OHH

OHH

CH2OH

1

2

3

4

5

6

1 +O

OH

OH

HO

HOOH

41

O

OH

OH

HO

HOOH

4

From 5-OH

From 4-OH

CHO

OHH

HHO

OHH

OHH

CH2OH

1

2

3

4

5

6

OHO

OH

HOOH

OH1

5+

OHO

OH

HOOH

OH

1

5

D-Glucose

Intramolecular Addition of OH to an Aldehyde or Ketone

3

The mechanism is the same as nucleophilic addition of OH to –CHO in acidic condition.

From 5-OH

Cannot do it from 4-OH!

D-FructoseCH2OH

O

HHO

OHH

OHH

CH2OH

OHO

HO

HO

OH

OH

1

2

3

4

5

6

D/L Configuration of Six-carbon Pyranoses (6-Membered Ring)

4

D-AldohexoseL-Aldohexose

Note: draw D and L sugars in specific chair conformation

OHO

OH

OH

OH OHH

OHO

HO

HO

OH

OH

H

O

pyranTail

Tail

O

OH

OH

1

6

5O

HOOH

156

Examples of Six-carbon Pyranoses

5

D-Allopyranose D-Altropyranose D-Glucopyranose D-Mannopyranose

D-Gulopyranose D-Idopyranose D-Galactopyranose L-Glucopyranose

OHO

OH

OH

OH OH

OHO

OH

OH

OH

OH

OHO

OH

HOOH OH

OHO

OH

HO

OH

OH

O

HO OH

OH

OH OH

O

HO OH

OH

OH

OH

O

HO OH

HOOH OH

OHO

HO

HO

OH

OH

Examples of Five-carbon Pyranoses

6

D-Xylopyranose D-Arabinpyranose L-Arabinpyranose

OHO

HOOH OH

O

HO

HOOH OH

O

HOHO

OH

OH

Note: draw sugars in specific chair conformation cannot determine the D and L like six-carbon pyranoses

OHO

OH15

6O

OH

OH

1

6

5

Examples of Furanoses (5-Membered Ring)

7

D-Ribofuranose D-Fructofuranose D-Glucofuranose D-Galactofuranose

furanO

O OH

OHHO

HO

O OH

OH

HO

HOOH

O

HO

HO

HO

OH

OH

O OH

OH

OH

HO OH

Common Pyranoses with Modified Functional Groups

8

D-Glucosamine D-Fucose L-Fucose L-Rhamnose

O

HO

HOOH OH

O

HO

HO

OH

OHOHO

OH

HONH2 OH

OHO

HO

OH

OH

9

Learning Check1. Which hydroxy group when added to the aldehyde functional group (C-1) of open chain glucose will produce the cyclic hemiacetal form shown below?

(a) The one that locates on C-2.(b) The one that locates on C-3.(c) The one that locates on C-4.(d) The one that locates on C-5.(e) None of the above

CHO

OHH

HHO

OHH

OHH

CH2OH

glucose (open chain)

glucose (cyclic hemiacetal)

1

2

3

4

5

6

OHO

OH

HOOH OH

10

Learning Check2. Which hydroxy group when added to the aldehyde functional group (C-1) of open chain glucose will produce the cyclic hemiacetal form shown below?

(a) The one that locates on C-2.(b) The one that locates on C-3.(c) The one that locates on C-4.(d) The one that locates on C-5.(e) None of the above

CHO

OHH

HHO

OHH

OHH

CH2OH

glucose (open chain)

glucose (cyclic hemiacetal)

1

2

3

4

5

6

O OH

OH

HO

HOOH

11

Learning Check3. Which of the following are D-sugars?

(a) I, II, III(b) I, II, IV(c) III, V(d) I, II, V(e) I, III, V

I

OHO

OH

HOOH OH

II

OHO

OH

HO

HO

OH

IV

O

HO OH

HOOH OH

O

HO

HO

OH

OHHO

III

OHO

HO

OH

OHHO

V

12

Learning Check4. Which of the following are L-sugars?

(a) I, II, III(b) I, II, IV(c) III, V(d) I, II, V(e) I, III, V

I

OHO

OH

HOOH OH

II

OHO

OH

HO

HO

OH

IV

O

HO OH

HOOH OH

O

HO

HO

OH

OHHO

III

OHO

HO

OH

OHHO

V

13

Learning Check5. RNA’s contain a carbohydrate unit as the backbone. Which of the following description regarding this carbohydrate unit is correct?

(a) It is a D-ketopentose.(b) It is a L-furanose.(c) It is a D-ribofuranose.(d) It is a D-ribopyranose.(e) None of the above.

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N

NN

N

H2N

O

OHO

H

PO

O-

O

O

N

NH2

ONO

OHO

H

PO

O-

O