Asymmetric Synthesis of All Stereoisomers of Demethylsorgolactone. Dependence of the Stimulatory Activity of Striga hermonthica and Orobanche crenata Seed Germination on the Absolute Configuration

Strigol and sorgolactone belong to the class of “strigolactones”, which are highly potent germination stimulants of seeds of the parasitic weeds Striga and Orobanche . The aim of the present work was to synthesize all four stereoisomers of demethylsorgolactone ( 6 ), which lacks the methyl group in the A-ring of naturally occurring sorgolactone, and to evaluate their activities in the stimulation of germination of Striga hermonthica and Orobanche crenata seeds. Two diastereomers of demethylsorgolactone ( 6 ) were prepared and resolved in the corresponding enantiomers. Bioassays revealed that the germination stimulatory activity of 6 is comparable to that of strigol and that there exist significant differences in activity among the individual stereoisomers.