Ajoene

April 15, 2019
I stink, but I could help kill microbes.
What molecule am I?

Ajoene is an unsaturated organosulfur compound found in small quantities (0.1%–0.5%) in garlic. Its name comes from ajo, the Spanish word for garlic, so it is therefore pronounced a-ho-ene. Ajoene’s odor mimics that of whole garlic.

The natural product is a mixture of E- and Z-stereoisomers in a ratio of ≈1:2. The E-isomer is shown. According to Dongbin Shin and co-workers at the Korea Food Research Institute (Gyeonggi‐do),

Commercial products typically have an E/Z ratio of ≈2, with a range of 0.6–2.5. . . . The E/Z ratio and yield depend on the polarity of the solvent system, reaction condition, and the type of fatty acids that are present during processing. It is known that the Z-isomer has a strong bioactivity compared to E-ajoene, while the E-isomer is more stable than the Z-isomer during storage.

For a relatively well-studied compound, little chemical and physical data for ajoene are available. Its hazard profile may also not be completely known.

Biologists and biochemists have long been interested in the potentially strong antimicrobial properties of ajoene, but neither purifying the natural product nor synthesizing it produced enough to work with. Recently, Thomas Wirth and colleagues at Cardiff University and Neem Biotech (both UK), seeking larger quantities of ajoene for drug research, developed a shorter, more efficient synthesis of the compound.

The researchers’ five-step procedure begins with an alkyl dibromide and proceeds through three selenium-containing intermediates until the selenium moiety is oxidatively cleaved with hydrogen peroxide to produce ajoene. A thioether group was converted to sulfoxide in the same step. The authors expanded the original milligram-scale synthesis to make the compound in >100-g quantities.

In initial antibacterial testing, the synthetic product performed as well as ajoene isolated from garlic.

Don't forget to celebrate National Garlic Day on April 19!

Ajoene fast facts

CAS Reg. No. 92285-01-3
Empirical formula C9H14OS3
Molar mass 234.39 g/mol
Appearance Colorless liquid
Boiling point 376 ºC (est.)
Water solubility 0.3 g/L (est.)

Ajoene hazard information

GHS classification*: not a hazardous substance or mixture

*Globally Harmonized System of Classification and Labeling of Chemicals.

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