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Lecture 28

Lecture 28. Get LP 9/10; due next Tuesday Sweeteners This Week in Lab: Spec Unknown Final Report Due Next Week in Lab: Synthetic #2 Final Report Due Remember to bring all graded PreLabs and Aldrich to lab. Sweeteners. Carbohydrates: Mono- and disaccharides Examples:

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Lecture 28

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  1. Lecture 28 • Get LP 9/10; due next Tuesday • Sweeteners • This Week in Lab: • Spec Unknown Final Report Due • Next Week in Lab: • Synthetic #2 Final Report Due • Remember to bring all graded PreLabs and Aldrich to lab

  2. Sweeteners Carbohydrates: Mono- and disaccharides Examples: Sugar, corn syrup, maple syrup, juice concentrates

  3. 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 1960s, 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

  4. Saccharin Sweetness: Shape must fit into specific receptors in taste buds. When shape is slightly modified, it is no longer sweet:

  5. Aspartame • Non-carbohydrate sweetener • Equal, NutraSweet Aspartame

  6. 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 • 200 times sweeter than sugar

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. 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.

  12. Aspartame Synthesis: Amide Formation

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

  14. 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

  15. Synthesis of Sucralose 6-step reaction sequence: React sucrose with tritylating agent (2) Acetylation of product from step (1) (3) Detritylation of step (2) product (4) Isomerization of the penta-acetate product from step (3) (5) Chlorination of step (4) product (6) Deacetylation of step (5) product

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