L-Aspartyl-L-Phenylalanine Methyl Ester

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L-Aspartyl-L-Phenylalanine Methyl Ester


L-aspartyl-L-phenylalanine methyl ester (ell-ass-par-TEEL ell-fee-no-AL-uh-neen METH-el ESS-ter) is an artificial sweetener more widely known as aspartame. It is sold under a number of brand names, including NutraSweet®, Equal®, Spoonful®, Benevia®, Indulge®, NatraTaste®, and Equal-Measure®. Unlike sugar, which is a carbohydrate, aspartame is a dipeptide, a compound made of two amino acids joined to each other. It is 180 to 200 times as sweet as sucrose (table sugar), but provides no calories to a person's diet. It is a satisfactory substitute for sugar, therefore, for people who must or wish to reduce their caloric intake.







Carbon, hydrogen, nitrogen, oxygen


Ester (organic)




294.30 g/mol


246.5°C (475.7°F)


Not applicable


Slightly soluble in water; insoluble in alcohol, benzene, ether, and most other organic solvents

Aspartame was discovered accidentally in 1965 by James M. Schlatter, an employee of the G. D. Searle pharmaceutical company. Schlatter was searching for a chemical compound that could be used to treat ulcers. L-aspartyl-L-phenylalanine methyl ester was one of the compounds he made during his investigations. He accidentally got some of the compound on his fingers, a fact that he did not notice until later in the day. Then, when he licked his fingers to pick up a piece of paper, he noticed the intensely sweet taste of the compound. To confirm his suspicions about the compound, he added some of it to his coffee—a practice that violates all laboratory safety rules!—and found that it was more than satisfactory as a substitute for sugar. Searle began the testing and application procedure needed to gain approval from the U.S. Food and Drug Administration, a long and drawn-out procedure that ended only in 1981, 25 years after its discovery.


Aspartame is made by a relatively simple procedure in which two amino acids, aspartic acid and phenylalanine, are reacted with each other to form a two-amino-acid product, called a dipeptide. The carboxylic acid group in the dipeptide is then reacted with methanol (methyl alcohol; CH3OH) to obtain the methyl ester of the compound. One problem that makes the preparation somewhat more difficult is that both aspartic acid and phenylalanine have stereoisomers. The term stereoisomer refers to two forms of a compound that contain the same kind and number of atoms, but differ in the orientation in space ("stereo-") of some of the atoms. Because of these stereoisomers, four different kinds of aspartame are formed during the preparation described above—D & D; L & L; D & L; L & D (the latter two are different from each other). Only one is the desired product, the one that contains only "L" stereoisomers.

Interesting Facts

  • The Aspartame Information Center claims that the compound is now used in more than 6,000 commercial products and consumed by more than 100 million people worldwide.


Aspartame's primary commercial use is as an artificial sweetener. Some of the products that contain aspartame are breath mints, carbonated soft drinks, cereals, chewing gum, sugar-free gelatin, hard candies, ice cream toppings, sugar-free ice cream, ready-to-drink iced tea, instant cocoa mix, jams and jellies, juice drinks, nutritional bars, protein nutritional drinks, diet puddings, sugar-free chocolate syrup, sugar-free cookies, table top sweeteners, and fat- and sugar-free yogurt. The compound is also used to a lesser extent as a flavor enhancer, a substance that intensifies an already-existing flavor.

The use of aspartame as a food additive in the United States has a long and complex history. As required for FDA approval, Searle conducted a number of studies to show that aspartame is safe for human consumption. Based on the results of those studies, the FDA first granted approval for the use of aspartame in certain types of foods on July 26, 1974. Less than a month later, two concerned citizens, James Turner and Dr. John Olney, filed a petition objecting to the FDA's decision, citing possible errors in Searle's testing procedures on aspartame. After continued studies extending over a seven-year period, the FDA once again approved aspartame for use in dry foods. A year later, the agency extended its approval for aspartame to dry beverage mixes and add-in sweeteners and, in 1983, to beverages and other foods.

The campaign against aspartame has not lessened over the years. Today, a number of individuals and groups maintain organizations and websites whose purpose it is to have aspartame banned as a food additive. Continued studies by the manufacturer and independent researchers seem to confirm the safety of aspartame, but have found that two groups of people do face some level of risk by ingesting the compound. The first group consists of people who seem to have some natural allergy to the compound and experience symptoms such as anxiety attacks, breathing difficulties, dizziness, unusual fatigue, headaches, heart palpitations, skin rashes, muscle spasms, nausea, numbness, respiratory allergies, weight gain, and memory loss. Individuals who experience such problems are encouraged to avoid eating or drinking products that contain aspartame.

A second group for whom aspartame is a far more serious problem consists of individuals with phenylketonuria. Phenylketonuria is a genetic disorder in which a person's body is unable to metabolize the amino acid phenylalanine, a component of aspartame. If phenylalanine is ingested by someone with phenylketonuria, the amino acid builds up in the body and causes a number of organic problems, including mental retardation, damage to the organs, and muscular disorders. Any product that contains aspartame is now required by law to have a warning label aimed at phenylketonuriacs so that they will not accidentally ingest the compound.

Words to Know

A compound made of two amino acids joined to each other.
A compound formed when methyl alcohol (methanol) reacts with an organic acid.
A genetic disorder in which a person's body is unable to metabolize the amino acid phenylalanine.
One of a pair of molecules, both of which have the same kinds and number of atoms, but which differ in how some of the atoms are oriented in relation to each other.


"Aspartame." Chemical Land 21. http://www.chemicalland21.com/lifescience/foco/ASPARTAME.htm (accessed on September 21, 2005).

"Aspartame Information Center." http://www.aspartame.org/ (accessed on September 21, 2005).

"Low-Calorie Sweeteners: Aspartame." Calorie Control Council. http://www.caloriecontrol.org/aspartame.html (accessed on September 21, 2005).

Metcalfe, Ed., et al. "Sweet Talking." The Ecologist (June 2000): 16.