Selective Activity Against Amastigote Forms of Trypanosoma cruzi and Leishmania infantum of Diastereomeric Dicentrine N-oxides

As part of our continuous research for the discovery of bioactive compounds against Trypanosoma cruzi and Leishmania infantum, the alkaloid (6aS)-dicentrine (1) was oxidized to afford (6aS,6S)- (2) and (6aS,6R)- (3) dicentrine-N-oxides. Evaluation of the cytotoxicity against NCTC cells indicated that 2 and 3 are non-toxic (CC50>200 mu M) whereas 1 demonstrated CC50 of 52.0 mu M. Concerning T. cruzi activity against amastigotes, derivatives 2 and 3 exhibited EC50 values of 9.9 mu M (SI>20.2) and 27.5 mu M (SI>7.3), respectively, but 1 is inactive (EC50>100 mu M). Otherwise, when tested against L. infantum amastigotes, 1 and 3 exhibited EC50 values of 10.3 mu M (SI=5.0) and 12.7 mu M (SI>15.7), respectively, being 2 inactive (EC50>100 mu M). Comparing the effects of positive controls benznidazol (EC50=6.5 mu M and SI>30.7) and miltefosine (EC50=10.2 mu M and SI=15.2), it was observed a selective antiparasitic activity to diastereomers 2 and 3 against T. cruzi and L. infantum. Considering stereochemical aspects, it was suggested that the configuration of the new stereocenter formed after oxidation of 1 played an important role in the bioactivity against amastigotes of both tested parasites.