Annonaceous Acetogenins from the Seeds of Annona squamosa. Non-adjacent Bis-tetrahydrofuranic Acetogenins.

Four non-adjacent bis-tetrahydrofuranic acetogenins, named squamostatins-B (2), -C (3), -D (4) and -E (5), have been isolated from the petroleum ether extract of Annona squamosa seeds. The structures of these acetogenins have been established on the basis of spectral evidence. C-15/C-16-threo, C-19/C-20-threo, C-23/C-24-erythro stereochemistry was assigned for squamostatins-B and -D, whereas C-15/C-16-threo, C-19/C-20-threo, C-23/C-24-threo stereochemistry was assigened for squamostatins-C and -E. All of these acetogenins, including squamostatin-A, have been established to have C-12/C-15-trans, C-20/C-23-trans stereochemistry by 13C-NMR comparison with synthetic model mono-tetrahydrofuranic compounds. An improved <13>C-NMR assignment of squamostatin-A is presented.