The final goal is to react the methyl ester of phenylalamine
with aspartic acid to give the dipeptide amide structure. A series
of reactions is required so that only the acid of the base amino
acid is reacted. The acid group on the side chain is protected
so that it does not react.
Many years were spent testing the product as required by the
FDA. In the almost two decades since first approval, testing
continues and the use of NutraSweet remains a rather controversial
issue. A search of the Internet will reveal many anecdotal but
scientifically undocumented bulletins regarding health risks
associated with the use of NutraSweet.
Phenylalanine is one of the "essential" amino acids,
meaning that humans must get it from their diet. It is a precursor
for the synthesis of tyrosine and several neurotransmitters.
Excess phenylalanine is broken down to fumarate and acetoacetate,
both of which are part of normal energy metabolism.
People who lack the enzyme to convert phenylalanine to tyrosine
are not able to metabolize phenylalanine normally. This condition
is called phenylketonuria, PKU, because excess phenylalanine
is instead converted to phenylketones which appear in the urine.
If it is not detected and treated, this condition can lead to
mental retardation. This was the first genetic disease for which
a routine screening test became available. Persons having this
genetic defect must monitor their intake of phenylalanine. For
this reason, products containing aspartame carry an information
label for phenylketonurics.