Reactions of Sugars Two major reactions: 1. Cyclization 2. Glycosylation Other reactions: Reduction Oxidation

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

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

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

Roles of Polycarbohydrates in Biological Systems 1. Structural elements 2. 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-  -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!

Structural Role of Carbohydrates Starch (potatoes): 1,4-  -linkage (see depiction on board):  -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-  -linkage to produce glucose  fuel! These same enzymes do not touch the 1,4-  -linkage of cellulose, but bacteria can hydrolyze cellulose. Bacteria live in some mammals, so these animals can eat plants.

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.

Amino Acids, Peptides & Proteins  -amino acid:

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.

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.

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

Aspartame: A Dipeptide Two main constituents: Phenylalanine Aspartic acid Goal: 1. Make the methyl ester of phenylalanine 2. Make a peptide (amide) bond between phenylalanine and aspartic acid Overall - two main steps to this synthesis