NMR-STUDIES OF CA2+ COMPLEXES OF ANNONACEOUS ACETOGENINS

C-13 NMR longitudinal relaxation times (T-1) have been determined for both annonacin (1) and squamocin (2) in the absence and presence of Ca 2+ ions. These data are used to assess structural changes that accompa ny complexations. Even though acetogenins of the Annonaceae present no ionophoric effects in biological studies with living cells, we assume that they have a role in the bioavailability of the cations in the ce ll membranes, due to both their lipophilic and polar natures. These re sults also show differences in the stoichiometry of the complexes of a mono-tetrahydrofuranic acetogenin and a bis-tetrahydrofuranic acetoge nin with Ca2+ ions.