Hypoglycin A

Sources

The entirety of the unripe ackee fruit is toxic and contains large amounts of hypoglycin. The fruit is safe to eat only when the fruit is allowed to fully open and expose the large black seeds while on the tree. The levels of the toxin decrease over time though from approximately 1000 ppm to around 0.1 ppm in the mature fruit.

Relatives of ackee, including lychee, longan, and rambutan, can contain enough α-(methylenecyclopropyl)glycine, a homologue of hypoglycin A, in their fruit to cause hypoglycemic encephalopathy in undernourished children, when consumed in large quantities.

Toxicity

Hypoglycin A is a protoxin, meaning that the molecule is not toxic in itself but is broken down into toxic products when ingested. The branched-chain alpha-keto acid dehydrogenase complex, that normally converts leucine, isoleucine, or valine into acyl-CoA derivatives, converts Hypoglycin A into highly toxic MCPA-CoA. The FAD cofactor necessary for the beta oxidation of fatty acids associates with the alpha carbon of MCPA-CoA creating an irreversible complex that disables the enzyme. In addition, MCPA-CoA blocks some enzymes that are required for gluconeogenesis.

The reduction in gluconeogenesis and the reduction in fatty acid oxidation are thought to be the cause of most of the symptoms of Jamaican vomiting sickness. The blocking of fatty acid metabolism causes cells to start using glycogen for energy. Once glycogen is depleted, the body is unable to produce more, which leads to severe hypoglycemia. These biochemical effects are detected by an excess of medium chain fatty acids in urine and acidosis. Key treatments are aimed at circumventing or counteracting the biochemical changes, and include IV fluids and glucose, and hemodialysis in the case of renal failure.

Synthesis

In 1958, John Carbon, William Martin, and Leo Swett were the first to synthesize hypoglycin A, in racemic form, starting from 2-bromopropene and ethyl diazoacetate to form the cyclopropane ring.{{citation |author1=Carbon, J. A. |author2=Martin, W. B. |author3=Swett, L. R. |journal=J. Am. Chem. Soc. |title=SYNTHESIS OF α-AMINO- METHYLENECYCLOPROPANEPROPIONIC ACID (HYPOGLYCIN A) |year=1958 |volume=80

References

References

1. (2018-06-13). "Ackee Fruit Toxicity".
2. (2013-07-01). "Seasonal pasture myopathy/atypical myopathy in North America associated with ingestion of hypoglycin A within seeds of the box elder tree". Equine Veterinary Journal.
3. (2017). "Association of acute toxic encephalopathy with litchi consumption in an outbreak in Muzaffarpur, India, 2014: a case-control study". The Lancet Global Health.
4. (2005-11-17). "THE ACKEE FRUIT (BLIGHIA SAPIDA) AND ITS ASSOCIATED TOXIC EFFECTS". [[University of British Columbia]].
5. (2015). "Probable Toxic Cause for Suspected Lychee-Linked Viral Encephalitis". [[Emerging Infectious Diseases]].
6. "Hypoglycin". [[TOXNET]].
7. (1992). "Asymmetric total synthesis of the individual diastereoisomers of hypoglycin A". Journal of the Chemical Society, Chemical Communications.
8. (1994). "Asymmetric total synthesis of the individual diastereoisomers of hypoglycin A.". Tetrahedron.