Amygdalin

This was one of two molecules for this week.
May 27, 2019
We “quacked”, but we’re not ducks.
What molecules are we?
Image of Amygdalin 3D Image of Amygdalin
Image of Amygdalin 3D Image of Amygdalin

Amygdalin (on the left) and its companion molecule laetrile (right) burst into the headlines in the 1950s as purported cancer cures. As scientific research soon determined, they are not effective for treating cancer—they are potent poisons.

Amygdalin occurs in many plants, notably in seeds of fruits in the Rosaceae family such as bitter almonds, apricots, and plums. Laetrile is a derivative of amygdalin formed by the hydrolytic removal of one glycoside group from the parent compound. The literature is a bit confusing because the names and laetrile sometimes are conflated. Both molecules are also erroneously termed vitamin B17.

Chemists Walter Norman Haworth and Birkett Wylam at Durham University (Newcastle upon Tyne, UK) elucidated the structure of amygdalin and synthesized it in 1923. Haworth was awarded the 1937 Nobel Prize in Chemistry for 1938.

From the 1950s through the 1970s, both compounds, under the name laetrile, were heavily promoted as a cure for many types of cancer. Rogue physicians and others established clinics in Mexico to which desperate patients flocked to receive the “cure” and other ineffective treatments. Science, however, prevailed: Laetrile was never approved by the US Food and Drug Administration or the European Commission.

The nitrile groups in amygdalin and laetrile are labile and easily removed as the cyanide ion by β-glucosidase enzymes in the human body. Cyanide, of course, is highly toxic; it is surprising that the compounds’ oral toxicity is given the mild hazard statement “harmful if swallowed”.

In 1981, Irving J. Lerner at the University of Minnesota Medical School (Minneapolis) summarized the laetrile hoax thus: "All prior forms of cancer quackery . . . pale in comparison with the laetrile crusade, the slickest, most sophisticated, and certainly the most remunerative cancer quack promotion in medical history." 

Amygdalin and laetrile* hazard information

GHS classification**: acute toxicity, oral, category 4
H302—Harmful if swallowed Chemical Safety Warning

*No safety data sheet for laetrile is available. Hazards are assumed to be the same as for amygdalin.
**Globally Harmonized System of Classification and Labeling of Chemicals. Explanation of pictograms.

Amygdalin fast facts

CAS Reg. No. 29883-15-6
Empirical formula C20H27NO11
Molar mass 457.43 g/mol
Appearance White to beige powder
Melting point 223–226 ºC
Water solubility 50 g/L

Laetrile fast facts

CAS Reg. No. 1332-94-1
Empirical formula C14H15NO7
Molar mass 309.27 g/mol
Appearance White powder
Melting point 214–216 ºC
Water solubility 83 g/L
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Learn more about this molecule from CAS, the most authoritative and comprehensive source for chemical information.

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