Reactions of Sugars

1. Reactions of Sugars Two major reactions: Cyclization Glycosylation Other reactions: Reduction Oxidation

2. Glycosides: Digitoxin • One component of the heart drug digitalis • A cardiac glycoside; classified as a steroid • Digitalis: powdered leaves of Digitalis pupurea (foxglove) • Excessive use of digitalis can produce xanthopsia (yellow vision) Digitoxin

3. Glycosides: Sucralose/Splenda • Carbohydrate-based sweetener • Made from sugar • 600 times sweeter than sugar

4. Sucralose/Splenda • Does not metabolize to produce energy, thus no calories • Only low calorie sweetener made from sugar • Heat stable - used in cooking and • baking • Discovery story: • In 1976 by Dr. Hough’s lab • at King’s College • From 1980 onwards, collaboration • with Tate & Lyle, a British sugar company, • and McNeil Specialty Products

5. Roles of Polycarbohydrates in Biological Systems • Structural elements • Address labels for proteins Structural • Glucose is polymerized in vivo to form two different linear polymers: cellulose and starch -glu-glu-glu-glu- Cellulose: 1,4-b-linkage (see depiction on board): • Rigid, rod-like (like a 2 x 4 plank) • Many opportunities for H-bonding (the “glue” that pulls the polymer chains together) • Very strong, so trees can grow >300 feet tall!

6. Structural Role of Carbohydrates Starch (potatoes): 1,4-a-linkage (see depiction on board): • a-linkage imparts a helical shape overall to the polymer - very different from cellulose • Intramolecular H-bonding, not so much intermolecular H-bonding, so polymer chains are not “glued” together • Water soluble, cellulose is not • Can be processed by mammals - a food source • Mammals contain enzymes which cleave (hydrolyze) the 1,4-a-linkage to produce glucose  fuel! These same enzymes do not touch the 1,4-b-linkage of cellulose, but bacteria can hydrolyze cellulose. Bacteria live in some mammals, so these animals can eat plants.

7. Carbohydrates: Address Labels • Many proteins need to be chaperoned to their final destinations in cell • compartments from their point of synthesis in the ribosome. • These proteins are tagged with an address label that directs it to its • proper location. • Address labels are oligosaccharides (carbohydrate chain 5-20 units long). • Address labels have very precise H-bonding pattern which encodes the • address’ information. This code is “read” by receptor proteins.

8. Amino Acids, Peptides & Proteins a-amino acid:

9. Amino Acids • Are >500 naturally occurring amino acids identified in living organisms • Humans synthesize 10 of the 20 they use. The other 10 are called essential amino acids.

10. Amino Acids, Peptides & Proteins • Peptides & proteins: • Derived from amino acids through peptide or amide bonds. • The amine and acid ends of amino acids couple to form amide (peptide) bonds • in peptides/proteins/enzymes. See board for further discussion. • Proteins fold into well-defined structures. The hydrophobic residues • segregate to the water-free interior, while the polar/charged residues favor • the exterior.

11. Aspartame • Discovery story: • In 1965 by Jim Schlatter • working on discovering new • treatments for gastric • ulcers. • Made a dipeptide intermediate, • which he spilled on his hand • Tested the dipeptide in coffee Aspartame • 4 calories per gram • 180 times sweeter than sugar

12. Aspartame: A Dipeptide Two main constituents: Phenylalanine Aspartic acid Goal: Make the methyl ester of phenylalanine 2. Make a peptide (amide) bond between phenylalanine and aspartic acid Overall - two main steps to this synthesis