1. 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 Main Menu Cyclic hemiketal

2. 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. From 5-OH From 4-OH D -Glucose

3. 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 -Fructose

4. D/L Configuration of Six-carbon Pyranoses (6-Membered Ring) 4 D -Aldohexose L -Aldohexose Note: draw D and L sugars in specific chair conformation pyran Tail

5. Examples of Six-carbon Pyranoses 5 D -Allopyranose D -Altropyranose D -Glucopyranose D -Mannopyranose D -Gulopyranose D -Idopyranose D -Galactopyranose L- Glucopyranose

6. Examples of Five-carbon Pyranoses 6 D -Xylopyranose D -Arabinpyranose L -Arabinpyranose Note: draw sugars in specific chair conformation cannot determine the D and L like six-carbon pyranoses

7. Examples of Furanoses (5-Membered Ring) 7 D -Ribofuranose D -Fructofuranose D -Glucofuranose D -Galactofuranose furan

8. Common Pyranoses with Modified Functional Groups 8 D -Glucosamine D -FucoseL-Fucose L -Rhamnose

9. 9 Learning Check 1. 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

10. 10 Learning Check 2. 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

11. 11 Learning Check 3. 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

12. 12 Learning Check 4. 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

13. 13 Learning Check 5. 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. Main Menu