Lecture 29 • Hand in Lecture Problem 10 • Sweeteners • Quiz 8 on Thursday in lecture • This Week in Lab: • Synthetic #2 Final Report; Lab Clean-up & Check-out! • Remember to bring all graded PreLabs and Aldrich to lab.
Sweeteners Carbohydrates: Mono- and disaccharides Examples: Sugar, corn syrup, maple syrup, juice concentrates
Saccharin • Non-carbohydrate sweetener • Sweet’N Low, Sugar Twin • Discovery Story: • In 1879 by Constantine Fahlberg • By 1907, saccharin was used by diabetics • Not metabolized in the body for energy • By 1960’s, used in diet soft drinks • Safety controversy due to findings of bladder tumors • in some male rats • More than 30 human studies conclude that it’s safe
Saccharin Sweetness: Shape must fit into specific receptors in taste buds. When shape is slightly modified, it is no longer sweet:
Aspartame • Non-carbohydrate sweetener • Equal, NutraSweet Aspartame
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 Aspartame is metabolized in the body into: methanol (wood alcohol), phenylalanine, and aspartic acid Phenylalanine is an essential amino acid and is a precursor for the synthesis of tyrosine and several neurotransmitters. Excess phenylalanine is broken down into fumarate and acetoacetate - normal energy metabolism.
Aspartame Safety concerns: If lacking the enzyme to convert phenylalanine to tyrosine, have phenylketonuria, PKU. Phenylalanine is then converted to phenylketones instead. PKU could lead to mental retardation if not detected or treated. Aspartame Products that contain aspartame carry an information label for phenylketonurics.
Aspartame Safety concerns: Reports of formaldehyde poisoning. Methanol quickly converts to formaldehyde in the body. Formaldehyde causes severe damage to the neurological system, immune system, and causes permanent genetic damage at extremely low doses. Aspartame
Aspartame Synthesis 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
Aspartame: Ester Synthesis Only the S enantiomer of phenylalanine is desired for use. The R and S enantiomers can be separated before the esterification reaction.
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
Quiz 8 • Reactions: • Electrophilic Aromatic Substitution Reactions: • Nitration • Friedel Crafts Alkylation & Acylation • Substitution Reactions: • Williamson Ether Synthesis • Elimination Reactions: • Dehydration of alcohols • Oxidation: • Epoxidation of alkenes • Of alcohols • Of benzylic carbons • Reduction: • Of alkenes • Of carbonyls • Esterification: • Fisher • Alternative (with anhydrides) • Enolate Chemistry: • Adol & Aldol Condensation • Mixed Aldol
Quiz 8 • Reactions: • Be able to draw out the mechanisms of only those • reactions that were given in lecture. Know the reagents • used for each reaction. • Special topics: • Drug candidates • Drug discovery process • Retrosynthetic analysis • Molecular modification • Sweeteners • Be able to identify a compound
Practice Quiz Problems Design a synthesis of the following ester. You can use either the Fisher esterification method or the alternative esterification method. Give the overall reaction equation with starting materials, reagents, and main organic product.