An expeditious preparation of all enantiopure diastereoisomers of aromatic A-ring analogues of strigolactones, germination stimulants for seeds of the parasitic weeds Striga and Orobanche

An expeditious manner to prepare all enantiopure diastereomers of aromatic A-ring strigolactone analogues is described. The racemic diastereoisomers of 8-methyl GR 24 and of its regioisomer 6-methyl GR 24 were prepared and separated, and subsequently chromatographed to give the pure enantiomers, using a Chiralcel OD® HPLC column. The biological activity of all enantiopure strigolactone analogues towards seeds of Striga hermonthica and Orobanche crenata was determined. The presence of a methyl group on position 8 of GR 24 did not result in increased biological activity, whereas a 6-methyl substituent on GR 24 resulted in higher percentages of germinated O. crenata seeds, when compared with GR 24.