Get LP 910 due next Tuesday

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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

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Sweeteners
Carbohydrates Mono- and disaccharides Examples
Sugar, corn syrup, maple syrup, juice concentrates
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Saccharin

• Non-carbohydrate sweetener
• SweetN 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 its
  safe

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

• Non-carbohydrate sweetener
• Equal, NutraSweet

Aspartame
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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

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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.
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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.
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Aspartame
Safety concerns Reports of formaldehyde poisonin
g. 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
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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
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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.
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Aspartame Synthesis Amide Formation

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Sucralose/Splenda

• Carbohydrate-based sweetener
• Made from sugar
• 600 times sweeter than sugar

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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. Houghs lab
• at Kings College
• From 1980 onwards, collaboration
• with Tate Lyle, a British sugar company,
• and McNeil Specialty Products

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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