Chromatographic separation of the n -hexane extract of the aerial part of Plectranthus barbatus led to the isolation of five abietane-type diterpenes: dehydroabietane ( 1 ); 5,6-didehydro-7-hydroxy-taxodone ( 2 ); taxodione ( 3 ); 20-deoxocarnosol ( 4 ) and 6α,11,12,-trihydroxy-7β,20-epoxy-8,11,13-abietatriene ( 5 ). The structures were determined using spectroscopic methods including one- and two-dimensional NMR methods. Compounds ( 1 )–( 3 ) and ( 5 ) are isolated here for the first time from the genus Plectranthus . The isolated abietane-type diterpenes tested in vitro for their antiprotozoal activity against erythrocytic schizonts of Plasmodium falciparum , intracellular amastigotes of Leishmania infantum and Trypanosoma cruzi and free trypomastigotes of T. brucei . Cytotoxicity was determined against fibroblast cell line MRC-5. Compound ( 2 ) 5,6-didehydro-7-hydroxy-taxodone showed remarkable activity with acceptable selectivity against P. falciparum (IC 50 9.2 μM, SI 10.4) and T. brucei (IC 50 1.9 μM, SI 50.5). Compounds ( 3 )–( 5 ) exhibited non-specific antiprotozoal activity due to high cytotoxicity. Compound ( 1 ) dehydroabietane showed no antiprotozoal potential.
【저자키워드】 cytotoxicity, Plasmodium, Leishmania, Trypanosoma, Antiprotozoal, Plectranthus barbatus, abietane-type diterpenoids,