Strigone, isolation and identification as a natural strigolactone from Houttuynia cordata

Abstract (+)-Strigone was described earlier in a paper on isolation of strigol and then recently examined for hyphal branching activity in arbuscular mycorrhizal fungi as a strigolactone. Herein, it was isolated from root exudates of Houttuynia cordata , and its structure was confirmed by direct comparison with synthetic standards in LC–MS/MS, GC–MS, and 1 H and 13 C NMR analyses. The stereochemistry of strigone was determined by comparing the CD spectra and RR t in chiral LC–MS/MS with those of synthetic (+)-strigone and (−)-strigone. Four stereoisomers of strigone exhibited clearly different levels of stimulation activity on the seeds of three root parasitic plants, Orobanche minor , Phelipanche ramosa , and Striga hermonthica . (+)-Strigone was a highly potent germination stimulant on S. hermonthica and also on P. ramosa , but less active than ent -2′- epi -strigone on O. minor . In addition to strigone, H. cordata was found to produce strigol, sorgomol, and 5-deoxystrigol, indicating that this plant produces mainly strigol-type strigolactones derived from 5-deoxystrigol.