Chemistry 263 Carbohydrates Chapter 22 in Solomons and Fryhlie, 11 th edition. Carbohydrates. In the beginning

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1 Chemistry 263 Carbohydrates Chapter 22 in Solomons and Fryhlie, 11 th edition Carbohydrates In the beginning 1

2 2 H2O + 2 NADP ADP + 3 Pi + light 2 NADPH + 2 H ATP + O2 2

3 Electron transport in plants bears a remarkable similarity to oxidative phosphorylation in mitochondria 3

4 So what happens to this energy trapped as ATP and NADPH? Enter the dark side of the Calvin Cycle 1 One of the molecules of 3-Phosphoglycerate is then used for synthesis of needed molecules such as glucose and on to cellulose (look at glycolysis in reverse below) 1 Actually, light independent is better since the enzymes involved are activated in the light. The Calvin cycle is more fully known as the Calvin-Benson-Bassham (CBB) after its discoverors Melvin Calvin, Andrew Benson, and James Bassham of UC Berkeley 4

5 Below is shown the Fischer projection for Ribulose-1,5-bisphosphate. How does the formation of an enolate allow CO2 to bond and ultimately give rise to 2 molecules of 3- phosphoglycerate on hydrolysis? Hint: If you count the oxygens in ribulose-1,5- bisphosphate + CO2 and compare to the number of oxygens in 2 3-phosphoglycerate, you will see the need for 1 more oxygen. Now what do you suppose could provide one oxygen? Ribulose-1,5-bisphosphate 3-Phosphoglycerate Interestingly, 3-phosphoglycerate is a central intermediate in glycolysis as well 5

6 So why do we say energy is trapped in ATP? For the same reason we consider acid anhydride to be a reactive species the presence of an acid anhydride linkage 6

7 22.1, 22.2: Structural Formulas for Monosaccharides & Mutarotation 7

8 22.4: Glycoside Formation Mechanistically Glycoside Formation 8

9 Glycoside Hydrolysis Mechanistically 9

10 10

11 22.5: Further Reactions of Carbohydrates Enolization, Tautomerization, and Isomerization Carbohydrate Protecting Groups Benzyl Ether Formation 11

12 Benzyl Ether Cleavage Exhaustive Methylation with Dimethyl Sulfate Regioselective Silyl Ether Formation Regioselective Silyl Ether Cleavage 12

13 [Acetate] Ester Formation Formation of Cyclic Acetals Question: How would you avoid forming the usual acetal between monosaccharides? 13

14 22.6: Oxidation Reactions of Monosaccharides Reducing Sugars Revisited Benedict s Reagent Question: What s wrong with this picture where ketoses are concerned? Question: Tollen s test uses [Ag(NH3)2] + and generates a silver mirror as a positive test for aldehydes and is used to distinguish between aldehydes and ketones. However, Tollen s test gives the same result as Benedict s reagent where reducing sugars are concerned. What s up with that? 14

15 Aldonic Acids From Monosaccharides & Bromine Water The mildly acidic conditions of the bromine water avoid complicating reactions. However, things are a tad more complicated in that oxidation is selective for the anomer, which can subsequently hydrolyse and reform a 5-membered lactone 15

16 Aldaric Acids From Monosaccharides & HNO3 16

17 22.7: Reduction Reactions of Monosaccharides Alditols 22.8: Reactions of Monosaccharides with Phenylhydrazine - Osazones Mechanistically 17

18 22.8: Synthesis and Degradation of Monosaccharides Kiliani-Fischer Synthesis 18

19 Ruff Degradation 22.10: The D Family of Aldoses 19

20 22.11: Fischer s Proof of the Structure of D-(+)-Glucose 20

21 22.12: Disaccharides Sucrose Maltose 21

22 So how do we know how monosaccharides are linked? Well, we do have to rely on and glycosidic enzymes to clue us in to the nature of the glycosidic linkage, but we can also employ a little organic chemistry fancy footwork to make our determination. Using maltose as an example 22

23 Lactose Cellobiose Interestingly, lactose can be broken down by the -glycosidic enzyme lactase; an enzyme that is feedback regulated (almost a pun there) and diminishes as a child matures. Cultures that have a tradition of using milk as a major source of calories have evolved the capacity to maintain lactase through adulthood. Europeans, West Asians, India, and parts of East Africa are among those who tolerate lactose in the adult population > 70 %. Those who s genetic roots trace to other parts of Africa, Eastern and Southeast Asia, the native peoples of Australia, and New Zealand, and Pacific Islanders have tolerance rates < 30 %. Further, cellobiose is not digestible but is being mass produced enzymatically by Nippon Paper Chemicals, Ltd. in part to help livestock gain weight. Apparently, as a non-digestible disaccharide cellobiose helps promote increased populations of beneficial hydrolytic gut flora consequently inproving digestion of foods in the lower intestine. These bacteria also compete against bacteria that are potentially harmful (such clostridium difficile which may take over during clindamycin treatment). As such these bacteria are known as probiotics, actually being beneficial to the health of the organism. Is it possible lactose intolerant individuals are improving the composition of their gut flora by drinking milk products? I think most would just rather opt for Lactaid 23

24 22.13: Polysaccharides 24

25 Cotton vs. Rayon 25