Hypoglycin A is a naturally occurring amino acid derivative found in the unripened fruit of the Ackee tree (Blighia sapida)[1] and in the seeds of the box elder tree (Acer negundo).[2] It is toxic if ingested, and is the causative agent of Jamaican vomiting sickness.[1] A 2017 Lancet report established a link between the consumption of unripened lychees (containing hypoglycin A or methylenecyclopropylglycine (MCPG)) resulting in hypoglycaemia and death from acute toxic encephalopathy.[3]
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.[4]
Relatives of Ackee, including lychee, longan, and rambutan, can contain enough α-(methylenecyclopropyl)glycine, a homologue of hypoglycin A, in their fruit to cause hypoglycemicencephalopathy in undernourished children, when consumed in large quantities.[5]
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.[6]
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.[7]
John Carbon's synthesis of Hypoglycin A
In 1992, Jack Baldwin, Robert Adlington, David Bebbington, and Andrew Russell accomplished the first asymmetric total synthesis of the individual diastereoisomers of hypoglycin A, using the Sharpless epoxidation to permit an asymmetric methylene cyclopropane synthesis.[8][9]1H NMR and circular dichroism studies identifies the major diastereoisomer of natural hypogycin A as (2S, 4R) and the minor diastereoisomer as (2S, 4S).
^Carbon, J. A.; Martin, W. B.; Swett, L. R. (1958), "SYNTHESIS OF α-AMINO- METHYLENECYCLOPROPANEPROPIONIC ACID (HYPOGLYCIN A)", J. Am. Chem. Soc., 80 (4): 1002, doi:10.1021/ja01537a066
^Baldwin, Jack E.; Adlington, Robert M.; Bebbington, David; Russell, Andrew T. (1992). "Asymmetric total synthesis of the individual diastereoisomers of hypoglycin A". Journal of the Chemical Society, Chemical Communications (17): 1249. doi:10.1039/c39920001249. ISSN0022-4936.
^Baldwin, Jack E.; Adlington, Robert M.; Bebbington, David; T. Russell, Andrew (1994). "Asymmetric total synthesis of the individual diastereoisomers of hypoglycin A.". Tetrahedron. 50 (41): 12015–12028. doi:10.1016/s0040-4020(01)89313-3. ISSN0040-4020.