Structural characterization of hypoglycin B, a diastereomeric dipeptide from the ackee fruit (Blighia sapida Koenig) by NMR experiments.

The dipeptide hypoglycin B, one of two toxins of the ackee fruit (Blighia sapida Koenig), was characterized for the first time by NMR spectral data, which led to the discovery that it exists naturally as a pair of diastereomers. No distinction was observed in the (1)H NMR signals of the diastereomers; however, complete and distinct (13)C NMR assignments for the individual diastereomers were made. The (13)C NMR spectrum of hypoglycin B compared very well with that of the corresponding signals in the spectrum for hypoglycin A, which is one of its constituent amino acids. The (1)H and (13)C NMR assignments were further supported by DEPT, gCOSY, gHSQC and gHMBC experiments.