A computational study of hypoglycin A, the toxin of the unripe Jamaican ackee fruit

Abstract

The optimised structure, harmonic vibrational frequencies and NMR chemical shifts of the neutral and zwitterionic forms of the (2S,4R) diastereoisomer of hypoglycin A, the toxic substance of the unripe fruit of the Jamaican ackee tree, were determined by MP2 and B3LYP calculations using a 6-31 + G(d,p) basis set. Computations on this unusual amino acid when embedded in a simulated water continuum were also undertaken and two stable conformations (‘staggered’ and ‘eclipsed’) of the zwitterionic isomer were predicted. The neutral form of hypoglycin is predicted to be the more stable isomer in the gas phase, but a study of the microsolvation of neutral hypoglycin by the sequential addition of water molecules suggests that at least three water molecules are required to make the zwitterion more stable than the neutral isomer.

Keywords:

• amino acid
• toxin
• zwitterion
• microsolvation