The behavior of G3 factor and of its methylated or fluorinated analogues G3Me and G3F, was studied under Fe(II) conditions. Degradation products were isolated and characterized in each case. The use of labelled compounds allowed us to propose mechanisms in which a tertiary radical is involved. This radical rearranges by 5-exo-trig cyclization, or disproportionates in the case of G3Me. A correlation between antiplasmodial activity and stability of this radical is proposed.