Synthesis and biological evaluation of the strigol analogue carba-GR24

Both geometrical isomers of the strigol analogue carba-GR24, (E)-3-[2-(4-methyl-5-oxo-2,5-dihydrofuran-2-yl)ethylidene]-3,3a,4,8b-tetrahydro-2H-indeno[1,2-b]furan-2-one (1) and 7 (Z isomer), were prepared separately. These analogues, in which the vinyl ether oxygen atom in GR24 has been replaced by a methylene function, are completely inactive for the stimulation of germination of seeds of the parasitic weeds Striga hermonthica and Orobanche crenata. Bioassays in which 1 was tested as an inhibitor of germination gave no indication as such. Keywords: Striga; Orobanche; germination; strigol analogue